migrate services to nullsafety (#62513)

NNBD migration for services

dev/tools/gen_keycodes/data/keyboard_key.tmpl

@@ -149,13 +149,15 @@ class LogicalKeyboardKey extends KeyboardKey {
 
   /// The debug string to print for this keyboard key, which will be null in
   /// release mode.
-  final String debugName;
+  final String? debugName;
 
   /// The Unicode string representing the character produced by a [RawKeyEvent].
   ///
   /// This value is useful for describing or matching mnemonic keyboard
   /// shortcuts.
   ///
+  /// This value can be null if there's no key label data for a key.
+  ///
   /// On most platforms this is a single code point, but it could contain any
   /// Unicode string. The `keyLabel` differs from [RawKeyEvent.character]
   /// because `keyLabel` only takes into account the key being pressed, not any
@@ -164,7 +166,7 @@ class LogicalKeyboardKey extends KeyboardKey {
   /// “o” for [keyLabel], but would return “ö” for [RawKeyEvent.character].
   ///
   /// {@macro flutter.services.RawKeyEventData.keyLabel}
-  final String keyLabel;
+  final String? keyLabel;
 
   @override
   int get hashCode => keyId.hashCode;
@@ -180,7 +182,7 @@ class LogicalKeyboardKey extends KeyboardKey {
 
   /// Returns the [LogicalKeyboardKey] constant that matches the given ID, or
   /// null, if not found.
-  static LogicalKeyboardKey findKeyByKeyId(int keyId) => _knownLogicalKeys[keyId];
+  static LogicalKeyboardKey? findKeyByKeyId(int keyId) => _knownLogicalKeys[keyId];
 
   /// Returns true if the given label represents a Unicode control character.
   ///
@@ -237,7 +239,7 @@ class LogicalKeyboardKey extends KeyboardKey {
   /// this is a [shiftLeft] key, this accessor will return the set
   /// `<LogicalKeyboardKey>{ shift }`.
   Set<LogicalKeyboardKey> get synonyms {
-    final LogicalKeyboardKey result = _synonyms[this];
+    final LogicalKeyboardKey? result = _synonyms[this];
     return result == null ? <LogicalKeyboardKey>{} : <LogicalKeyboardKey>{result};
   }
 
@@ -250,7 +252,7 @@ class LogicalKeyboardKey extends KeyboardKey {
   static Set<LogicalKeyboardKey> collapseSynonyms(Set<LogicalKeyboardKey> input) {
     final Set<LogicalKeyboardKey> result = <LogicalKeyboardKey>{};
     for (final LogicalKeyboardKey key in input) {
-      final LogicalKeyboardKey synonym = _synonyms[key];
+      final LogicalKeyboardKey? synonym = _synonyms[key];
       result.add(synonym ?? key);
     }
     return result;
@@ -434,11 +436,11 @@ class PhysicalKeyboardKey extends KeyboardKey {
 
   /// The debug string to print for this keyboard key, which will be null in
   /// release mode.
-  final String debugName;
+  final String? debugName;
 
   /// Finds a known [PhysicalKeyboardKey] that matches the given USB HID usage
   /// code.
-  static PhysicalKeyboardKey findKeyByCode(int usageCode) => _knownPhysicalKeys[usageCode];
+  static PhysicalKeyboardKey? findKeyByCode(int usageCode) => _knownPhysicalKeys[usageCode];
 
   @override
   int get hashCode => usbHidUsage.hashCode;

packages/flutter/lib/services.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 /// Platform services exposed to Flutter apps.
 ///
 /// To use, import `package:flutter/services.dart`.

packages/flutter/lib/src/services/asset_bundle.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 import 'dart:convert';
@@ -181,11 +180,11 @@ abstract class CachingAssetBundle extends AssetBundle {
     assert(parser != null);
     if (_structuredDataCache.containsKey(key))
       return _structuredDataCache[key] as Future<T>;
-    Completer<T> completer;
-    Future<T> result;
+    Completer<T>? completer;
+    Future<T>? result;
     loadString(key, cache: false).then<T>(parser).then<void>((T value) {
       result = SynchronousFuture<T>(value);
-      _structuredDataCache[key] = result;
+      _structuredDataCache[key] = result!;
       if (completer != null) {
         // We already returned from the loadStructuredData function, which means
         // we are in the asynchronous mode. Pass the value to the completer. The
@@ -196,7 +195,7 @@ abstract class CachingAssetBundle extends AssetBundle {
     if (result != null) {
       // The code above ran synchronously, and came up with an answer.
       // Return the SynchronousFuture that we created above.
-      return result;
+      return result!;
     }
     // The code above hasn't yet run its "then" handler yet. Let's prepare a
     // completer for it to use when it does run.
@@ -217,7 +216,7 @@ class PlatformAssetBundle extends CachingAssetBundle {
   @override
   Future<ByteData> load(String key) async {
     final Uint8List encoded = utf8.encoder.convert(Uri(path: Uri.encodeFull(key)).path);
-    final ByteData asset =
+    final ByteData? asset =
         await defaultBinaryMessenger.send('flutter/assets', encoded.buffer.asByteData());
     if (asset == null)
       throw FlutterError('Unable to load asset: $key');

packages/flutter/lib/src/services/autofill.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'package:flutter/foundation.dart';
 import 'text_input.dart';
@@ -629,9 +628,9 @@ class AutofillConfiguration {
   /// Creates autofill related configuration information that can be sent to the
   /// platform.
   const AutofillConfiguration({
-    @required this.uniqueIdentifier,
-    @required this.autofillHints,
-    this.currentEditingValue,
+    required this.uniqueIdentifier,
+    required this.autofillHints,
+    required this.currentEditingValue,
   }) : assert(uniqueIdentifier != null),
        assert(autofillHints != null);
 
@@ -749,7 +748,7 @@ abstract class AutofillScope {
   /// this [AutofillScope].
   ///
   /// Returns null if there's no matching [AutofillClient].
-  AutofillClient getAutofillClient(String autofillId);
+  AutofillClient? getAutofillClient(String autofillId);
 
   /// The collection of [AutofillClient]s currently tied to this [AutofillScope].
   ///
@@ -767,8 +766,8 @@ abstract class AutofillScope {
 @immutable
 class _AutofillScopeTextInputConfiguration extends TextInputConfiguration {
   _AutofillScopeTextInputConfiguration({
-    @required this.allConfigurations,
-    @required TextInputConfiguration currentClientConfiguration,
+    required this.allConfigurations,
+    required TextInputConfiguration currentClientConfiguration,
   }) : assert(allConfigurations != null),
        assert(currentClientConfiguration != null),
        super(inputType: currentClientConfiguration.inputType,

packages/flutter/lib/src/services/binary_messenger.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 import 'dart:typed_data';
@@ -12,7 +11,7 @@ import 'package:flutter/foundation.dart';
 import 'binding.dart';
 
 /// A function which takes a platform message and asynchronously returns an encoded response.
-typedef MessageHandler = Future<ByteData> Function(ByteData message);
+typedef MessageHandler = Future<ByteData?> Function(ByteData? message);
 
 /// A messenger which sends binary data across the Flutter platform barrier.
 ///
@@ -27,13 +26,13 @@ abstract class BinaryMessenger {
   /// from [Window.onPlatformMessage].
   ///
   /// To register a handler for a given message channel, see [setMessageHandler].
-  Future<void> handlePlatformMessage(String channel, ByteData data, ui.PlatformMessageResponseCallback callback);
+  Future<void> handlePlatformMessage(String channel, ByteData? data, ui.PlatformMessageResponseCallback? callback);
 
   /// Send a binary message to the platform plugins on the given channel.
   ///
   /// Returns a [Future] which completes to the received response, undecoded,
   /// in binary form.
-  Future<ByteData> send(String channel, ByteData message);
+  Future<ByteData?> send(String channel, ByteData? message);
 
   /// Set a callback for receiving messages from the platform plugins on the
   /// given channel, without decoding them.
@@ -43,7 +42,7 @@ abstract class BinaryMessenger {
   /// argument.
   ///
   /// The handler's return value, if non-null, is sent as a response, unencoded.
-  void setMessageHandler(String channel, MessageHandler handler);
+  void setMessageHandler(String channel, MessageHandler? handler);
 
   /// Returns true if the `handler` argument matches the `handler` previously
   /// passed to [setMessageHandler].
@@ -63,7 +62,7 @@ abstract class BinaryMessenger {
   ///
   /// This is intended for testing. Messages intercepted in this manner are not
   /// sent to platform plugins.
-  void setMockMessageHandler(String channel, MessageHandler handler);
+  void setMockMessageHandler(String channel, MessageHandler? handler);
 
   /// Returns true if the `handler` argument matches the `handler` previously
   /// passed to [setMockMessageHandler].
@@ -104,5 +103,5 @@ BinaryMessenger get defaultBinaryMessenger {
     }
     return true;
   }());
-  return ServicesBinding.instance.defaultBinaryMessenger;
+  return ServicesBinding.instance!.defaultBinaryMessenger;
 }

packages/flutter/lib/src/services/binding.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 import 'dart:typed_data';
@@ -31,14 +30,14 @@ mixin ServicesBinding on BindingBase, SchedulerBinding {
     _restorationManager = createRestorationManager();
     window.onPlatformMessage = defaultBinaryMessenger.handlePlatformMessage;
     initLicenses();
-    SystemChannels.system.setMessageHandler(handleSystemMessage);
+    SystemChannels.system.setMessageHandler((dynamic message) => handleSystemMessage(message as Object));
     SystemChannels.lifecycle.setMessageHandler(_handleLifecycleMessage);
     readInitialLifecycleStateFromNativeWindow();
   }
 
   /// The current [ServicesBinding], if one has been created.
-  static ServicesBinding get instance => _instance;
-  static ServicesBinding _instance;
+  static ServicesBinding? get instance => _instance;
+  static ServicesBinding? _instance;
 
   /// The default instance of [BinaryMessenger].
   ///
@@ -46,7 +45,7 @@ mixin ServicesBinding on BindingBase, SchedulerBinding {
   /// keeps track of which handlers have been registered on each channel so
   /// it may dispatch incoming messages to the registered handler.
   BinaryMessenger get defaultBinaryMessenger => _defaultBinaryMessenger;
-  BinaryMessenger _defaultBinaryMessenger;
+  late BinaryMessenger _defaultBinaryMessenger;
 
   /// Creates a default [BinaryMessenger] instance that can be used for sending
   /// platform messages.
@@ -110,7 +109,7 @@ mixin ServicesBinding on BindingBase, SchedulerBinding {
     await rawLicenses.future;
     final Completer<List<LicenseEntry>> parsedLicenses = Completer<List<LicenseEntry>>();
     scheduleTask(() async {
-      parsedLicenses.complete(compute(_parseLicenses, await rawLicenses.future, debugLabel: 'parseLicenses'));
+      parsedLicenses.complete(compute<String, List<LicenseEntry>>(_parseLicenses, await rawLicenses.future, debugLabel: 'parseLicenses'));
     }, Priority.animation);
     await parsedLicenses.future;
     yield* Stream<LicenseEntry>.fromIterable(await parsedLicenses.future);
@@ -183,18 +182,18 @@ mixin ServicesBinding on BindingBase, SchedulerBinding {
     if (lifecycleState != null) {
       return;
     }
-    final AppLifecycleState state = _parseAppLifecycleMessage(window.initialLifecycleState);
+    final AppLifecycleState? state = _parseAppLifecycleMessage(window.initialLifecycleState);
     if (state != null) {
       handleAppLifecycleStateChanged(state);
     }
   }
 
-  Future<String> _handleLifecycleMessage(String message) async {
-    handleAppLifecycleStateChanged(_parseAppLifecycleMessage(message));
+  Future<String?> _handleLifecycleMessage(String? message) async {
+    handleAppLifecycleStateChanged(_parseAppLifecycleMessage(message!)!);
     return null;
   }
 
-  static AppLifecycleState _parseAppLifecycleMessage(String message) {
+  static AppLifecycleState? _parseAppLifecycleMessage(String message) {
     switch (message) {
       case 'AppLifecycleState.paused':
         return AppLifecycleState.paused;
@@ -218,7 +217,7 @@ mixin ServicesBinding on BindingBase, SchedulerBinding {
   /// [createRestorationManager], which is called to create the instance
   /// returned by this getter.
   RestorationManager get restorationManager => _restorationManager;
-  RestorationManager _restorationManager;
+  late RestorationManager _restorationManager;
 
   /// Creates the [RestorationManager] instance available via
   /// [restorationManager].
@@ -248,15 +247,15 @@ class _DefaultBinaryMessenger extends BinaryMessenger {
   static final Map<String, MessageHandler> _mockHandlers =
       <String, MessageHandler>{};
 
-  Future<ByteData> _sendPlatformMessage(String channel, ByteData message) {
-    final Completer<ByteData> completer = Completer<ByteData>();
+  Future<ByteData?> _sendPlatformMessage(String channel, ByteData? message) {
+    final Completer<ByteData?> completer = Completer<ByteData?>();
     // ui.window is accessed directly instead of using ServicesBinding.instance.window
     // because this method might be invoked before any binding is initialized.
     // This issue was reported in #27541. It is not ideal to statically access
     // ui.window because the Window may be dependency injected elsewhere with
     // a different instance. However, static access at this location seems to be
     // the least bad option.
-    ui.window.sendPlatformMessage(channel, message, (ByteData reply) {
+    ui.window.sendPlatformMessage(channel, message, (ByteData? reply) {
       try {
         completer.complete(reply);
       } catch (exception, stack) {
@@ -274,16 +273,16 @@ class _DefaultBinaryMessenger extends BinaryMessenger {
   @override
   Future<void> handlePlatformMessage(
     String channel,
-    ByteData data,
-    ui.PlatformMessageResponseCallback callback,
+    ByteData? data,
+    ui.PlatformMessageResponseCallback? callback,
   ) async {
-    ByteData response;
+    ByteData? response;
     try {
-      final MessageHandler handler = _handlers[channel];
+      final MessageHandler? handler = _handlers[channel];
       if (handler != null) {
         response = await handler(data);
       } else {
-        ui.channelBuffers.push(channel, data, callback);
+        ui.channelBuffers.push(channel, data, callback!);
         callback = null;
       }
     } catch (exception, stack) {
@@ -301,20 +300,20 @@ class _DefaultBinaryMessenger extends BinaryMessenger {
   }
 
   @override
-  Future<ByteData> send(String channel, ByteData message) {
-    final MessageHandler handler = _mockHandlers[channel];
+  Future<ByteData?> send(String channel, ByteData? message) {
+    final MessageHandler? handler = _mockHandlers[channel];
     if (handler != null)
       return handler(message);
     return _sendPlatformMessage(channel, message);
   }
 
   @override
-  void setMessageHandler(String channel, MessageHandler handler) {
+  void setMessageHandler(String channel, MessageHandler? handler) {
     if (handler == null)
       _handlers.remove(channel);
     else
       _handlers[channel] = handler;
-    ui.channelBuffers.drain(channel, (ByteData data, ui.PlatformMessageResponseCallback callback) async {
+    ui.channelBuffers.drain(channel, (ByteData? data, ui.PlatformMessageResponseCallback callback) async {
       await handlePlatformMessage(channel, data, callback);
     });
   }
@@ -323,7 +322,7 @@ class _DefaultBinaryMessenger extends BinaryMessenger {
   bool checkMessageHandler(String channel, MessageHandler handler) => _handlers[channel] == handler;
 
   @override
-  void setMockMessageHandler(String channel, MessageHandler handler) {
+  void setMockMessageHandler(String channel, MessageHandler? handler) {
     if (handler == null)
       _mockHandlers.remove(channel);
     else

packages/flutter/lib/src/services/clipboard.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 
@@ -20,7 +19,7 @@ class ClipboardData {
   const ClipboardData({ this.text });
 
   /// Plain text variant of this clipboard data.
-  final String text;
+  final String? text;
 }
 
 /// Utility methods for interacting with the system's clipboard.
@@ -54,13 +53,13 @@ class Clipboard {
   ///
   /// Returns a future which completes to null if the data could not be
   /// obtained, and to a [ClipboardData] object if it could.
-  static Future<ClipboardData> getData(String format) async {
-    final Map<String, dynamic> result = await SystemChannels.platform.invokeMethod(
+  static Future<ClipboardData?> getData(String format) async {
+    final Map<String, dynamic>? result = await SystemChannels.platform.invokeMethod(
       'Clipboard.getData',
       format,
     );
     if (result == null)
       return null;
-    return ClipboardData(text: result['text'] as String);
+    return ClipboardData(text: result['text'] as String?);
   }
 }

packages/flutter/lib/src/services/font_loader.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 import 'dart:typed_data';
@@ -64,7 +63,7 @@ class FontLoader {
             (Uint8List list) => loadFont(list, family)
         )
     );
-    return Future.wait(loadFutures.toList());
+    await Future.wait(loadFutures.toList());
   }
 
   /// Hook called to load a font asset into the engine.

packages/flutter/lib/src/services/haptic_feedback.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 

packages/flutter/lib/src/services/keyboard_key.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 // DO NOT EDIT -- DO NOT EDIT -- DO NOT EDIT
 // This file is generated by dev/tools/gen_keycodes/bin/gen_keycodes.dart and
@@ -149,13 +148,15 @@ class LogicalKeyboardKey extends KeyboardKey {
 
   /// The debug string to print for this keyboard key, which will be null in
   /// release mode.
-  final String debugName;
+  final String? debugName;
 
   /// The Unicode string representing the character produced by a [RawKeyEvent].
   ///
   /// This value is useful for describing or matching mnemonic keyboard
   /// shortcuts.
   ///
+  /// This value can be null if there's no key label data for a key.
+  ///
   /// On most platforms this is a single code point, but it could contain any
   /// Unicode string. The `keyLabel` differs from [RawKeyEvent.character]
   /// because `keyLabel` only takes into account the key being pressed, not any
@@ -164,7 +165,7 @@ class LogicalKeyboardKey extends KeyboardKey {
   /// “o” for [keyLabel], but would return “ö” for [RawKeyEvent.character].
   ///
   /// {@macro flutter.services.RawKeyEventData.keyLabel}
-  final String keyLabel;
+  final String? keyLabel;
 
   @override
   int get hashCode => keyId.hashCode;
@@ -180,7 +181,7 @@ class LogicalKeyboardKey extends KeyboardKey {
 
   /// Returns the [LogicalKeyboardKey] constant that matches the given ID, or
   /// null, if not found.
-  static LogicalKeyboardKey findKeyByKeyId(int keyId) => _knownLogicalKeys[keyId];
+  static LogicalKeyboardKey? findKeyByKeyId(int keyId) => _knownLogicalKeys[keyId];
 
   /// Returns true if the given label represents a Unicode control character.
   ///
@@ -237,7 +238,7 @@ class LogicalKeyboardKey extends KeyboardKey {
   /// this is a [shiftLeft] key, this accessor will return the set
   /// `<LogicalKeyboardKey>{ shift }`.
   Set<LogicalKeyboardKey> get synonyms {
-    final LogicalKeyboardKey result = _synonyms[this];
+    final LogicalKeyboardKey? result = _synonyms[this];
     return result == null ? <LogicalKeyboardKey>{} : <LogicalKeyboardKey>{result};
   }
 
@@ -250,7 +251,7 @@ class LogicalKeyboardKey extends KeyboardKey {
   static Set<LogicalKeyboardKey> collapseSynonyms(Set<LogicalKeyboardKey> input) {
     final Set<LogicalKeyboardKey> result = <LogicalKeyboardKey>{};
     for (final LogicalKeyboardKey key in input) {
-      final LogicalKeyboardKey synonym = _synonyms[key];
+      final LogicalKeyboardKey? synonym = _synonyms[key];
       result.add(synonym ?? key);
     }
     return result;
@@ -2087,11 +2088,11 @@ class PhysicalKeyboardKey extends KeyboardKey {
 
   /// The debug string to print for this keyboard key, which will be null in
   /// release mode.
-  final String debugName;
+  final String? debugName;
 
   /// Finds a known [PhysicalKeyboardKey] that matches the given USB HID usage
   /// code.
-  static PhysicalKeyboardKey findKeyByCode(int usageCode) => _knownPhysicalKeys[usageCode];
+  static PhysicalKeyboardKey? findKeyByCode(int usageCode) => _knownPhysicalKeys[usageCode];
 
   @override
   int get hashCode => usbHidUsage.hashCode;

packages/flutter/lib/src/services/keyboard_maps.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 // DO NOT EDIT -- DO NOT EDIT -- DO NOT EDIT
 // This file is generated by dev/tools/gen_keycodes/bin/gen_keycodes.dart and

packages/flutter/lib/src/services/message_codec.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:typed_data';
 
@@ -25,12 +24,12 @@ abstract class MessageCodec<T> {
   /// Encodes the specified [message] in binary.
   ///
   /// Returns null if the message is null.
-  ByteData encodeMessage(T message);
+  ByteData? encodeMessage(T message);
 
   /// Decodes the specified [message] from binary.
   ///
   /// Returns null if the message is null.
-  T decodeMessage(ByteData message);
+  T decodeMessage(ByteData? message);
 }
 
 /// An command object representing the invocation of a named method.
@@ -68,7 +67,7 @@ abstract class MethodCodec {
   ByteData encodeMethodCall(MethodCall methodCall);
 
   /// Decodes the specified [methodCall] from binary.
-  MethodCall decodeMethodCall(ByteData methodCall);
+  MethodCall decodeMethodCall(ByteData? methodCall);
 
   /// Decodes the specified result [envelope] from binary.
   ///
@@ -83,7 +82,7 @@ abstract class MethodCodec {
   ///
   /// The specified error [code], human-readable error [message], and error
   /// [details] correspond to the fields of [PlatformException].
-  ByteData encodeErrorEnvelope({ @required String code, String message, dynamic details });
+  ByteData encodeErrorEnvelope({ required String code, String? message, dynamic details });
 }
 
 
@@ -105,7 +104,7 @@ class PlatformException implements Exception {
   /// [message], and with the optional error [details] which must be a valid
   /// value for the [MethodCodec] involved in the interaction.
   PlatformException({
-    @required this.code,
+    required this.code,
     this.message,
     this.details,
   }) : assert(code != null);
@@ -114,7 +113,7 @@ class PlatformException implements Exception {
   final String code;
 
   /// A human-readable error message, possibly null.
-  final String message;
+  final String? message;
 
   /// Error details, possibly null.
   final dynamic details;
@@ -139,7 +138,7 @@ class MissingPluginException implements Exception {
   MissingPluginException([this.message]);
 
   /// A human-readable error message, possibly null.
-  final String message;
+  final String? message;
 
   @override
   String toString() => 'MissingPluginException($message)';

packages/flutter/lib/src/services/message_codecs.dart

@@ -2,12 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:convert';
 import 'dart:typed_data';
 
-import 'package:flutter/foundation.dart' show ReadBuffer, WriteBuffer, required;
+import 'package:flutter/foundation.dart' show ReadBuffer, WriteBuffer;
 
 import 'message_codec.dart';
 
@@ -19,35 +18,35 @@ import 'message_codec.dart';
 /// When sending outgoing messages from Android, be sure to use direct `ByteBuffer`
 /// as opposed to indirect. The `wrap()` API provides indirect buffers by default
 /// and you will get empty `ByteData` objects in Dart.
-class BinaryCodec implements MessageCodec<ByteData> {
+class BinaryCodec implements MessageCodec<ByteData?> {
   /// Creates a [MessageCodec] with unencoded binary messages represented using
   /// [ByteData].
   const BinaryCodec();
 
   @override
-  ByteData decodeMessage(ByteData message) => message;
+  ByteData? decodeMessage(ByteData? message) => message;
 
   @override
-  ByteData encodeMessage(ByteData message) => message;
+  ByteData? encodeMessage(ByteData? message) => message;
 }
 
 /// [MessageCodec] with UTF-8 encoded String messages.
 ///
 /// On Android, messages will be represented using `java.util.String`.
 /// On iOS, messages will be represented using `NSString`.
-class StringCodec implements MessageCodec<String> {
+class StringCodec implements MessageCodec<String?> {
   /// Creates a [MessageCodec] with UTF-8 encoded String messages.
   const StringCodec();
 
   @override
-  String decodeMessage(ByteData message) {
+  String? decodeMessage(ByteData? message) {
     if (message == null)
       return null;
     return utf8.decoder.convert(message.buffer.asUint8List(message.offsetInBytes, message.lengthInBytes));
   }
 
   @override
-  ByteData encodeMessage(String message) {
+  ByteData? encodeMessage(String? message) {
     if (message == null)
       return null;
     final Uint8List encoded = utf8.encoder.convert(message);
@@ -82,17 +81,17 @@ class JSONMessageCodec implements MessageCodec<dynamic> {
   const JSONMessageCodec();
 
   @override
-  ByteData encodeMessage(dynamic message) {
+  ByteData? encodeMessage(dynamic message) {
     if (message == null)
       return null;
     return const StringCodec().encodeMessage(json.encode(message));
   }
 
   @override
-  dynamic decodeMessage(ByteData message) {
+  dynamic decodeMessage(ByteData? message) {
     if (message == null)
       return message;
-    return json.decode(const StringCodec().decodeMessage(message));
+    return json.decode(const StringCodec().decodeMessage(message)!);
   }
 }
 
@@ -123,11 +122,11 @@ class JSONMethodCodec implements MethodCodec {
     return const JSONMessageCodec().encodeMessage(<String, dynamic>{
       'method': call.method,
       'args': call.arguments,
-    });
+    })!;
   }
 
   @override
-  MethodCall decodeMethodCall(ByteData methodCall) {
+  MethodCall decodeMethodCall(ByteData? methodCall) {
     final dynamic decoded = const JSONMessageCodec().decodeMessage(methodCall);
     if (decoded is! Map)
       throw FormatException('Expected method call Map, got $decoded');
@@ -158,13 +157,13 @@ class JSONMethodCodec implements MethodCodec {
 
   @override
   ByteData encodeSuccessEnvelope(dynamic result) {
-    return const JSONMessageCodec().encodeMessage(<dynamic>[result]);
+    return const JSONMessageCodec().encodeMessage(<dynamic>[result])!;
   }
 
   @override
-  ByteData encodeErrorEnvelope({ @required String code, String message, dynamic details }) {
+  ByteData encodeErrorEnvelope({ required String code, String? message, dynamic details }) {
     assert(code != null);
-    return const JSONMessageCodec().encodeMessage(<dynamic>[code, message, details]);
+    return const JSONMessageCodec().encodeMessage(<dynamic>[code, message, details])!;
   }
 }
 
@@ -281,7 +280,7 @@ class StandardMessageCodec implements MessageCodec<dynamic> {
   static const int _valueMap = 13;
 
   @override
-  ByteData encodeMessage(dynamic message) {
+  ByteData? encodeMessage(dynamic message) {
     if (message == null)
       return null;
     final WriteBuffer buffer = WriteBuffer();
@@ -290,7 +289,7 @@ class StandardMessageCodec implements MessageCodec<dynamic> {
   }
 
   @override
-  dynamic decodeMessage(ByteData message) {
+  dynamic decodeMessage(ByteData? message) {
     if (message == null)
       return null;
     final ReadBuffer buffer = ReadBuffer(message);
@@ -444,7 +443,7 @@ class StandardMessageCodec implements MessageCodec<dynamic> {
         return buffer.getFloat64List(length);
       case _valueList:
         final int length = readSize(buffer);
-        final dynamic result = List<dynamic>(length);
+        final dynamic result = List<dynamic>.filled(length, null, growable: false);
         for (int i = 0; i < length; i++)
           result[i] = readValue(buffer);
         return result;
@@ -529,8 +528,8 @@ class StandardMethodCodec implements MethodCodec {
   }
 
   @override
-  MethodCall decodeMethodCall(ByteData methodCall) {
-    final ReadBuffer buffer = ReadBuffer(methodCall);
+  MethodCall decodeMethodCall(ByteData? methodCall) {
+    final ReadBuffer buffer = ReadBuffer(methodCall!);
     final dynamic method = messageCodec.readValue(buffer);
     final dynamic arguments = messageCodec.readValue(buffer);
     if (method is String && !buffer.hasRemaining)
@@ -548,7 +547,7 @@ class StandardMethodCodec implements MethodCodec {
   }
 
   @override
-  ByteData encodeErrorEnvelope({ @required String code, String message, dynamic details }) {
+  ByteData encodeErrorEnvelope({ required String code, String? message, dynamic details }) {
     final WriteBuffer buffer = WriteBuffer();
     buffer.putUint8(1);
     messageCodec.writeValue(buffer, code);

packages/flutter/lib/src/services/platform_channel.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 import 'dart:typed_data';
@@ -36,7 +35,7 @@ class BasicMessageChannel<T> {
   ///
   /// The [name] and [codec] arguments cannot be null. The default [ServicesBinding.defaultBinaryMessenger]
   /// instance is used if [binaryMessenger] is null.
-  const BasicMessageChannel(this.name, this.codec, { BinaryMessenger binaryMessenger })
+  const BasicMessageChannel(this.name, this.codec, { BinaryMessenger? binaryMessenger })
       : assert(name != null),
         assert(codec != null),
         _binaryMessenger = binaryMessenger;
@@ -49,7 +48,7 @@ class BasicMessageChannel<T> {
 
   /// The messenger which sends the bytes for this channel, not null.
   BinaryMessenger get binaryMessenger => _binaryMessenger ?? defaultBinaryMessenger;
-  final BinaryMessenger _binaryMessenger;
+  final BinaryMessenger? _binaryMessenger;
 
   /// Sends the specified [message] to the platform plugins on this channel.
   ///
@@ -72,7 +71,7 @@ class BasicMessageChannel<T> {
     if (handler == null) {
       binaryMessenger.setMessageHandler(name, null);
     } else {
-      binaryMessenger.setMessageHandler(name, (ByteData message) async {
+      binaryMessenger.setMessageHandler(name, (ByteData? message) async {
         return codec.encodeMessage(await handler(codec.decodeMessage(message)));
       });
     }
@@ -93,7 +92,7 @@ class BasicMessageChannel<T> {
     if (handler == null) {
       binaryMessenger.setMockMessageHandler(name, null);
     } else {
-      binaryMessenger.setMockMessageHandler(name, (ByteData message) async {
+      binaryMessenger.setMockMessageHandler(name, (ByteData? message) async {
         return codec.encodeMessage(await handler(codec.decodeMessage(message)));
       });
     }
@@ -128,7 +127,7 @@ class MethodChannel {
   ///
   /// The [name] and [codec] arguments cannot be null. The default [ServicesBinding.defaultBinaryMessenger]
   /// instance is used if [binaryMessenger] is null.
-  const MethodChannel(this.name, [this.codec = const StandardMethodCodec(), BinaryMessenger binaryMessenger ])
+  const MethodChannel(this.name, [this.codec = const StandardMethodCodec(), BinaryMessenger? binaryMessenger ])
       : assert(name != null),
         assert(codec != null),
         _binaryMessenger = binaryMessenger;
@@ -143,12 +142,12 @@ class MethodChannel {
   ///
   /// The messenger may not be null.
   BinaryMessenger get binaryMessenger => _binaryMessenger ?? defaultBinaryMessenger;
-  final BinaryMessenger _binaryMessenger;
+  final BinaryMessenger? _binaryMessenger;
 
   @optionalTypeArgs
-  Future<T> _invokeMethod<T>(String method, { bool missingOk, dynamic arguments }) async {
+  Future<T?> _invokeMethod<T>(String method, { required bool missingOk, dynamic arguments }) async {
     assert(method != null);
-    final ByteData result = await binaryMessenger.send(
+    final ByteData? result = await binaryMessenger.send(
       name,
       codec.encodeMethodCall(MethodCall(method, arguments)),
     );
@@ -330,7 +329,7 @@ class MethodChannel {
   ///  * <https://api.flutter.dev/javadoc/io/flutter/plugin/common/MethodCall.html>
   ///    for how to access method call arguments on Android.
   @optionalTypeArgs
-  Future<T> invokeMethod<T>(String method, [ dynamic arguments ]) {
+  Future<T?> invokeMethod<T>(String method, [ dynamic arguments ]) {
     return _invokeMethod<T>(method, missingOk: false, arguments: arguments);
   }
 
@@ -343,8 +342,8 @@ class MethodChannel {
   /// See also:
   ///
   ///  * [invokeMethod], which this call delegates to.
-  Future<List<T>> invokeListMethod<T>(String method, [ dynamic arguments ]) async {
-    final List<dynamic> result = await invokeMethod<List<dynamic>>(method, arguments);
+  Future<List<T>?> invokeListMethod<T>(String method, [ dynamic arguments ]) async {
+    final List<dynamic>? result = await invokeMethod<List<dynamic>?>(method, arguments);
     return result?.cast<T>();
   }
 
@@ -357,8 +356,8 @@ class MethodChannel {
   /// See also:
   ///
   ///  * [invokeMethod], which this call delegates to.
-  Future<Map<K, V>> invokeMapMethod<K, V>(String method, [ dynamic arguments ]) async {
-    final Map<dynamic, dynamic> result = await invokeMethod<Map<dynamic, dynamic>>(method, arguments);
+  Future<Map<K, V>?> invokeMapMethod<K, V>(String method, [ dynamic arguments ]) async {
+    final Map<dynamic, dynamic>? result = await invokeMethod<Map<dynamic, dynamic>?>(method, arguments);
     return result?.cast<K, V>();
   }
 
@@ -376,13 +375,13 @@ class MethodChannel {
   /// completes with a [MissingPluginException], an empty reply is sent
   /// similarly to what happens if no method call handler has been set.
   /// Any other exception results in an error envelope being sent.
-  void setMethodCallHandler(Future<dynamic> handler(MethodCall call)) {
+  void setMethodCallHandler(Future<dynamic> Function(MethodCall call)? handler) {
     _methodChannelHandlers[this] = handler;
     binaryMessenger.setMessageHandler(
       name,
       handler == null
         ? null
-        : (ByteData message) => _handleAsMethodCall(message, handler),
+        : (ByteData? message) => _handleAsMethodCall(message, handler),
     );
   }
 
@@ -415,7 +414,7 @@ class MethodChannel {
     _methodChannelMockHandlers[this] = handler;
     binaryMessenger.setMockMessageHandler(
       name,
-      handler == null ? null : (ByteData message) => _handleAsMethodCall(message, handler),
+      handler == null ? null : (ByteData? message) => _handleAsMethodCall(message, handler),
     );
   }
 
@@ -426,7 +425,7 @@ class MethodChannel {
   /// handler for the specified channel has not been altered by a previous test.
   bool checkMockMethodCallHandler(Future<dynamic> handler(MethodCall call)) => _methodChannelMockHandlers[this] == handler;
 
-  Future<ByteData> _handleAsMethodCall(ByteData message, Future<dynamic> handler(MethodCall call)) async {
+  Future<ByteData?> _handleAsMethodCall(ByteData? message, Future<dynamic> handler(MethodCall call)) async {
     final MethodCall call = codec.decodeMethodCall(message);
     try {
       return codec.encodeSuccessEnvelope(await handler(call));
@@ -454,20 +453,20 @@ class OptionalMethodChannel extends MethodChannel {
     : super(name, codec);
 
   @override
-  Future<T> invokeMethod<T>(String method, [ dynamic arguments ]) async {
+  Future<T?> invokeMethod<T>(String method, [ dynamic arguments ]) async {
     return super._invokeMethod<T>(method, missingOk: true, arguments: arguments);
   }
 
   @override
-  Future<List<T>> invokeListMethod<T>(String method, [ dynamic arguments ]) async {
-    final List<dynamic> result = await invokeMethod<List<dynamic>>(method, arguments);
-    return result.cast<T>();
+  Future<List<T>?> invokeListMethod<T>(String method, [ dynamic arguments ]) async {
+    final List<dynamic>? result = await invokeMethod<List<dynamic>>(method, arguments);
+    return result?.cast<T>();
   }
 
   @override
-  Future<Map<K, V>> invokeMapMethod<K, V>(String method, [ dynamic arguments ]) async {
-    final Map<dynamic, dynamic> result = await invokeMethod<Map<dynamic, dynamic>>(method, arguments);
-    return result.cast<K, V>();
+  Future<Map<K, V>?> invokeMapMethod<K, V>(String method, [ dynamic arguments ]) async {
+    final Map<dynamic, dynamic>? result = await invokeMethod<Map<dynamic, dynamic>>(method, arguments);
+    return result?.cast<K, V>();
   }
 
 }
@@ -494,7 +493,7 @@ class EventChannel {
   ///
   /// Neither [name] nor [codec] may be null. The default [ServicesBinding.defaultBinaryMessenger]
   /// instance is used if [binaryMessenger] is null.
-  const EventChannel(this.name, [this.codec = const StandardMethodCodec(), BinaryMessenger binaryMessenger])
+  const EventChannel(this.name, [this.codec = const StandardMethodCodec(), BinaryMessenger? binaryMessenger])
       : assert(name != null),
         assert(codec != null),
         _binaryMessenger = binaryMessenger;
@@ -507,7 +506,7 @@ class EventChannel {
 
   /// The messenger used by this channel to send platform messages, not null.
   BinaryMessenger get binaryMessenger => _binaryMessenger ?? defaultBinaryMessenger;
-  final BinaryMessenger _binaryMessenger;
+  final BinaryMessenger? _binaryMessenger;
 
   /// Sets up a broadcast stream for receiving events on this channel.
   ///
@@ -524,9 +523,9 @@ class EventChannel {
   /// only when stream listener count changes from 1 to 0.
   Stream<dynamic> receiveBroadcastStream([ dynamic arguments ]) {
     final MethodChannel methodChannel = MethodChannel(name, codec);
-    StreamController<dynamic> controller;
+    late StreamController<dynamic> controller;
     controller = StreamController<dynamic>.broadcast(onListen: () async {
-      binaryMessenger.setMessageHandler(name, (ByteData reply) async {
+      binaryMessenger.setMessageHandler(name, (ByteData? reply) async {
         if (reply == null) {
           controller.close();
         } else {

packages/flutter/lib/src/services/platform_messages.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 import 'dart:typed_data';
@@ -67,7 +66,7 @@ class BinaryMessages {
     'Use defaultBinaryMessenger.send instead. '
     'This feature was deprecated after v1.6.5.'
   )
-  static Future<ByteData> send(String channel, ByteData message) {
+  static Future<ByteData?> send(String channel, ByteData? message) {
     return _binaryMessenger.send(channel, message);
   }
 
@@ -83,7 +82,7 @@ class BinaryMessages {
     'Use defaultBinaryMessenger.setMessageHandler instead. '
     'This feature was deprecated after v1.6.5.'
   )
-  static void setMessageHandler(String channel, Future<ByteData> handler(ByteData message)) {
+  static void setMessageHandler(String channel, Future<ByteData?> Function(ByteData? message) handler) {
     _binaryMessenger.setMessageHandler(channel, handler);
   }
 
@@ -102,7 +101,7 @@ class BinaryMessages {
     'Use defaultBinaryMessenger.setMockMessageHandler instead. '
     'This feature was deprecated after v1.6.5.'
   )
-  static void setMockMessageHandler(String channel, Future<ByteData> handler(ByteData message)) {
+  static void setMockMessageHandler(String channel, Future<ByteData?> Function(ByteData? message) handler) {
     _binaryMessenger.setMockMessageHandler(channel, handler);
   }
 }

packages/flutter/lib/src/services/raw_keyboard.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 import 'dart:io';
@@ -138,7 +137,7 @@ abstract class RawKeyEventData {
   /// null. If the given key only appears in one place on the keyboard, returns
   /// [KeyboardSide.all] if pressed. Never returns [KeyboardSide.any], because
   /// that doesn't make sense in this context.
-  KeyboardSide getModifierSide(ModifierKey key);
+  KeyboardSide? getModifierSide(ModifierKey key);
 
   /// Returns true if a CTRL modifier key was pressed at the time of this event,
   /// regardless of which side of the keyboard it is on.
@@ -166,8 +165,8 @@ abstract class RawKeyEventData {
 
   /// Returns a map of modifier keys that were pressed at the time of this
   /// event, and the keyboard side or sides that the key was on.
-  Map<ModifierKey, KeyboardSide> get modifiersPressed {
-    final Map<ModifierKey, KeyboardSide> result = <ModifierKey, KeyboardSide>{};
+  Map<ModifierKey, KeyboardSide?> get modifiersPressed {
+    final Map<ModifierKey, KeyboardSide?> result = <ModifierKey, KeyboardSide?>{};
     for (final ModifierKey key in ModifierKey.values) {
       if (isModifierPressed(key)) {
         result[key] = getModifierSide(key);
@@ -212,7 +211,7 @@ abstract class RawKeyEventData {
   /// complexities of managing keyboard input, like showing a soft keyboard or
   /// interacting with an input method editor (IME).
   /// {@endtemplate}
-  String get keyLabel;
+  String? get keyLabel;
 }
 
 /// Defines the interface for raw key events.
@@ -243,7 +242,7 @@ abstract class RawKeyEvent with Diagnosticable {
   /// Initializes fields for subclasses, and provides a const constructor for
   /// const subclasses.
   const RawKeyEvent({
-    @required this.data,
+    required this.data,
     this.character,
   });
 
@@ -256,40 +255,40 @@ abstract class RawKeyEvent with Diagnosticable {
     switch (keymap) {
       case 'android':
         data = RawKeyEventDataAndroid(
-          flags: message['flags'] as int ?? 0,
-          codePoint: message['codePoint'] as int ?? 0,
-          keyCode: message['keyCode'] as int ?? 0,
-          plainCodePoint: message['plainCodePoint'] as int ?? 0,
-          scanCode: message['scanCode'] as int ?? 0,
-          metaState: message['metaState'] as int ?? 0,
-          eventSource: message['source'] as int ?? 0,
-          vendorId: message['vendorId'] as int ?? 0,
-          productId: message['productId'] as int ?? 0,
-          deviceId: message['deviceId'] as int ?? 0,
-          repeatCount: message['repeatCount'] as int ?? 0,
+          flags: message['flags'] as int? ?? 0,
+          codePoint: message['codePoint'] as int? ?? 0,
+          keyCode: message['keyCode'] as int? ?? 0,
+          plainCodePoint: message['plainCodePoint'] as int? ?? 0,
+          scanCode: message['scanCode'] as int? ?? 0,
+          metaState: message['metaState'] as int? ?? 0,
+          eventSource: message['source'] as int? ?? 0,
+          vendorId: message['vendorId'] as int? ?? 0,
+          productId: message['productId'] as int? ?? 0,
+          deviceId: message['deviceId'] as int? ?? 0,
+          repeatCount: message['repeatCount'] as int? ?? 0,
         );
         break;
       case 'fuchsia':
         data = RawKeyEventDataFuchsia(
-          hidUsage: message['hidUsage'] as int ?? 0,
-          codePoint: message['codePoint'] as int ?? 0,
-          modifiers: message['modifiers'] as int ?? 0,
+          hidUsage: message['hidUsage'] as int? ?? 0,
+          codePoint: message['codePoint'] as int? ?? 0,
+          modifiers: message['modifiers'] as int? ?? 0,
         );
         break;
       case 'macos':
         data = RawKeyEventDataMacOs(
-            characters: message['characters'] as String ?? '',
-            charactersIgnoringModifiers: message['charactersIgnoringModifiers'] as String ?? '',
-            keyCode: message['keyCode'] as int ?? 0,
-            modifiers: message['modifiers'] as int ?? 0);
+            characters: message['characters'] as String? ?? '',
+            charactersIgnoringModifiers: message['charactersIgnoringModifiers'] as String? ?? '',
+            keyCode: message['keyCode'] as int? ?? 0,
+            modifiers: message['modifiers'] as int? ?? 0);
         break;
       case 'linux':
         data = RawKeyEventDataLinux(
-            keyHelper: KeyHelper(message['toolkit'] as String ?? ''),
-            unicodeScalarValues: message['unicodeScalarValues'] as int ?? 0,
-            keyCode: message['keyCode'] as int ?? 0,
-            scanCode: message['scanCode'] as int ?? 0,
-            modifiers: message['modifiers'] as int ?? 0,
+            keyHelper: KeyHelper(message['toolkit'] as String? ?? ''),
+            unicodeScalarValues: message['unicodeScalarValues'] as int? ?? 0,
+            keyCode: message['keyCode'] as int? ?? 0,
+            scanCode: message['scanCode'] as int? ?? 0,
+            modifiers: message['modifiers'] as int? ?? 0,
             isDown: message['type'] == 'keydown');
         break;
       case 'web':
@@ -428,7 +427,7 @@ abstract class RawKeyEvent with Diagnosticable {
   /// composing text, use the [TextField] or [CupertinoTextField] widgets, since
   /// those automatically handle many of the complexities of managing keyboard
   /// input.
-  final String character;
+  final String? character;
 
   /// Platform-specific information about the key event.
   final RawKeyEventData data;
@@ -449,8 +448,8 @@ abstract class RawKeyEvent with Diagnosticable {
 class RawKeyDownEvent extends RawKeyEvent {
   /// Creates a key event that represents the user pressing a key.
   const RawKeyDownEvent({
-    @required RawKeyEventData data,
-    String character,
+    required RawKeyEventData data,
+    String? character,
   }) : super(data: data, character: character);
 }
 
@@ -462,8 +461,8 @@ class RawKeyDownEvent extends RawKeyEvent {
 class RawKeyUpEvent extends RawKeyEvent {
   /// Creates a key event that represents the user releasing a key.
   const RawKeyUpEvent({
-    @required RawKeyEventData data,
-    String character,
+    required RawKeyEventData data,
+    String? character,
   }) : super(data: data, character: character);
 }
 
@@ -557,13 +556,10 @@ class RawKeyboard {
   ///    focus.
   ///  * [addListener], to add passive key event listeners that do not stop event
   ///    propagation.
-  RawKeyEventHandler keyEventHandler;
+  RawKeyEventHandler? keyEventHandler;
 
   Future<dynamic> _handleKeyEvent(dynamic message) async {
     final RawKeyEvent event = RawKeyEvent.fromMessage(message as Map<String, dynamic>);
-    if (event == null) {
-      return;
-    }
     if (event.data is RawKeyEventDataMacOs && event.logicalKey == LogicalKeyboardKey.fn) {
       // On macOS laptop keyboards, the fn key is used to generate home/end and
       // f1-f12, but it ALSO generates a separate down/up event for the fn key
@@ -595,7 +591,7 @@ class RawKeyboard {
     // Send the key event to the keyEventHandler, then send the appropriate
     // response to the platform so that it can resolve the event's handling.
     // Defaults to false if keyEventHandler is null.
-    final bool handled = keyEventHandler != null && keyEventHandler(event);
+    final bool handled = keyEventHandler != null && keyEventHandler!(event);
     assert(handled != null, 'keyEventHandler returned null, which is not allowed');
     return <String, dynamic>{ 'handled': handled };
   }
@@ -656,15 +652,15 @@ class RawKeyboard {
     // pressed/released while the app doesn't have focus, to make sure that
     // _keysPressed reflects reality at all times.
 
-    final Map<ModifierKey, KeyboardSide> modifiersPressed = event.data.modifiersPressed;
+    final Map<ModifierKey, KeyboardSide?> modifiersPressed = event.data.modifiersPressed;
     final Map<PhysicalKeyboardKey, LogicalKeyboardKey> modifierKeys = <PhysicalKeyboardKey, LogicalKeyboardKey>{};
     for (final ModifierKey key in modifiersPressed.keys) {
-      final Set<PhysicalKeyboardKey> mappedKeys = _modifierKeyMap[_ModifierSidePair(key, modifiersPressed[key])];
+      final Set<PhysicalKeyboardKey> mappedKeys = _modifierKeyMap[_ModifierSidePair(key, modifiersPressed[key])]!;
       assert(mappedKeys != null,
         'Platform key support for ${Platform.operatingSystem} is '
         'producing unsupported modifier combinations.');
       for (final PhysicalKeyboardKey physicalModifier in mappedKeys) {
-        modifierKeys[physicalModifier] = _allModifiers[physicalModifier];
+        modifierKeys[physicalModifier] = _allModifiers[physicalModifier]!;
       }
     }
     _allModifiersExceptFn.keys.forEach(_keysPressed.remove);
@@ -695,7 +691,7 @@ class _ModifierSidePair extends Object {
   const _ModifierSidePair(this.modifier, this.side);
 
   final ModifierKey modifier;
-  final KeyboardSide side;
+  final KeyboardSide? side;
 
   @override
   bool operator ==(Object other) {

packages/flutter/lib/src/services/raw_keyboard_android.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'package:flutter/foundation.dart';
 
@@ -148,7 +147,7 @@ class RawKeyEventDataAndroid extends RawKeyEventData {
 
   // Android only reports a single code point for the key label.
   @override
-  String get keyLabel => plainCodePoint == 0 ? null : String.fromCharCode(plainCodePoint & _kCombiningCharacterMask);
+  String? get keyLabel => plainCodePoint == 0 ? null : String.fromCharCode(plainCodePoint & _kCombiningCharacterMask);
 
   @override
   PhysicalKeyboardKey get physicalKey {
@@ -161,7 +160,7 @@ class RawKeyEventDataAndroid extends RawKeyEventData {
     // our own DPAD physical keys. The logical key will still match "arrowUp",
     // etc.
     if (eventSource & _sourceJoystick == _sourceJoystick) {
-      final LogicalKeyboardKey foundKey = kAndroidToLogicalKey[keyCode];
+      final LogicalKeyboardKey? foundKey = kAndroidToLogicalKey[keyCode];
       if (foundKey == LogicalKeyboardKey.arrowUp) {
         return PhysicalKeyboardKey.arrowUp;
       }
@@ -183,7 +182,7 @@ class RawKeyEventDataAndroid extends RawKeyEventData {
     // Look to see if the keyCode is a printable number pad key, so that a
     // difference between regular keys (e.g. "=") and the number pad version
     // (e.g. the "=" on the number pad) can be determined.
-    final LogicalKeyboardKey numPadKey = kAndroidNumPadMap[keyCode];
+    final LogicalKeyboardKey? numPadKey = kAndroidNumPadMap[keyCode];
     if (numPadKey != null) {
       return numPadKey;
     }
@@ -192,18 +191,18 @@ class RawKeyEventDataAndroid extends RawKeyEventData {
     // constant, or construct a new Unicode-based key from it. Don't mark it as
     // autogenerated, since the label uniquely identifies an ID from the Unicode
     // plane.
-    if (keyLabel != null && keyLabel.isNotEmpty && !LogicalKeyboardKey.isControlCharacter(keyLabel)) {
+    if (keyLabel != null && keyLabel!.isNotEmpty && !LogicalKeyboardKey.isControlCharacter(keyLabel!)) {
       final int combinedCodePoint = plainCodePoint & _kCombiningCharacterMask;
       final int keyId = LogicalKeyboardKey.unicodePlane | (combinedCodePoint & LogicalKeyboardKey.valueMask);
       return LogicalKeyboardKey.findKeyByKeyId(keyId) ?? LogicalKeyboardKey(
         keyId,
         keyLabel: keyLabel,
-        debugName: kReleaseMode ? null : 'Key ${keyLabel.toUpperCase()}',
+        debugName: kReleaseMode ? null : 'Key ${keyLabel!.toUpperCase()}',
       );
     }
 
     // Look to see if the keyCode is one we know about and have a mapping for.
-    LogicalKeyboardKey newKey = kAndroidToLogicalKey[keyCode];
+    LogicalKeyboardKey? newKey = kAndroidToLogicalKey[keyCode];
     if (newKey != null) {
       return newKey;
     }
@@ -232,7 +231,6 @@ class RawKeyEventDataAndroid extends RawKeyEventData {
       case KeyboardSide.right:
         return metaState & rightMask != 0;
     }
-    return false;
   }
 
   @override
@@ -258,12 +256,11 @@ class RawKeyEventDataAndroid extends RawKeyEventData {
       case ModifierKey.symbolModifier:
         return metaState & modifierSym != 0;
     }
-    return false;
   }
 
   @override
-  KeyboardSide getModifierSide(ModifierKey key) {
-    KeyboardSide findSide(int leftMask, int rightMask) {
+  KeyboardSide? getModifierSide(ModifierKey key) {
+    KeyboardSide? findSide(int leftMask, int rightMask) {
       final int combinedMask = leftMask | rightMask;
       final int combined = metaState & combinedMask;
       if (combined == leftMask) {
@@ -292,9 +289,6 @@ class RawKeyEventDataAndroid extends RawKeyEventData {
       case ModifierKey.symbolModifier:
         return KeyboardSide.all;
     }
-
-    assert(false, 'Not handling $key type properly.');
-    return null;
   }
 
   // Modifier key masks.

packages/flutter/lib/src/services/raw_keyboard_fuchsia.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'package:flutter/foundation.dart';
 
@@ -62,7 +61,7 @@ class RawKeyEventDataFuchsia extends RawKeyEventData {
 
   // Fuchsia only reports a single code point for the key label.
   @override
-  String get keyLabel => codePoint == 0 ? null : String.fromCharCode(codePoint);
+  String? get keyLabel => codePoint == 0 ? null : String.fromCharCode(codePoint);
 
   @override
   LogicalKeyboardKey get logicalKey {
@@ -77,7 +76,7 @@ class RawKeyEventDataFuchsia extends RawKeyEventData {
     }
 
     // Look to see if the hidUsage is one we know about and have a mapping for.
-    LogicalKeyboardKey newKey = kFuchsiaToLogicalKey[hidUsage | LogicalKeyboardKey.hidPlane];
+    LogicalKeyboardKey? newKey = kFuchsiaToLogicalKey[hidUsage | LogicalKeyboardKey.hidPlane];
     if (newKey != null) {
       return newKey;
     }
@@ -109,7 +108,6 @@ class RawKeyEventDataFuchsia extends RawKeyEventData {
       case KeyboardSide.right:
         return modifiers & rightMask != 0;
     }
-    return false;
   }
 
   @override
@@ -133,12 +131,11 @@ class RawKeyEventDataFuchsia extends RawKeyEventData {
         // Fuchsia doesn't have masks for these keys (yet).
         return false;
     }
-    return false;
   }
 
   @override
-  KeyboardSide getModifierSide(ModifierKey key) {
-    KeyboardSide findSide(int leftMask, int rightMask, int combinedMask) {
+  KeyboardSide? getModifierSide(ModifierKey key) {
+    KeyboardSide? findSide(int leftMask, int rightMask, int combinedMask) {
       final int combined = modifiers & combinedMask;
       if (combined == leftMask) {
         return KeyboardSide.left;
@@ -168,9 +165,6 @@ class RawKeyEventDataFuchsia extends RawKeyEventData {
         // Fuchsia doesn't support these modifiers, so they can't be pressed.
         return null;
     }
-
-    assert(false, 'Not handling $key type properly.');
-    return null;
   }
 
   // Keyboard modifier masks for Fuchsia modifiers.

packages/flutter/lib/src/services/raw_keyboard_linux.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'package:flutter/foundation.dart';
 
@@ -24,12 +23,12 @@ class RawKeyEventDataLinux extends RawKeyEventData {
   /// The [keyHelper], [scanCode], [unicodeScalarValues], [keyCode], and [modifiers],
   /// arguments must not be null.
   const RawKeyEventDataLinux({
-    @required this.keyHelper,
+    required this.keyHelper,
     this.unicodeScalarValues = 0,
     this.scanCode = 0,
     this.keyCode = 0,
     this.modifiers = 0,
-    @required this.isDown,
+    required this.isDown,
   }) : assert(scanCode != null),
        assert(unicodeScalarValues != null),
        assert((unicodeScalarValues & ~LogicalKeyboardKey.valueMask) == 0),
@@ -71,7 +70,7 @@ class RawKeyEventDataLinux extends RawKeyEventData {
   final bool isDown;
 
   @override
-  String get keyLabel => unicodeScalarValues == 0 ? null : String.fromCharCode(unicodeScalarValues);
+  String? get keyLabel => unicodeScalarValues == 0 ? null : String.fromCharCode(unicodeScalarValues);
 
   @override
   PhysicalKeyboardKey get physicalKey => kLinuxToPhysicalKey[scanCode] ?? PhysicalKeyboardKey.none;
@@ -81,7 +80,7 @@ class RawKeyEventDataLinux extends RawKeyEventData {
     // Look to see if the keyCode is a printable number pad key, so that a
     // difference between regular keys (e.g. "=") and the number pad version
     // (e.g. the "=" on the number pad) can be determined.
-    final LogicalKeyboardKey numPadKey = keyHelper.numpadKey(keyCode);
+    final LogicalKeyboardKey? numPadKey = keyHelper.numpadKey(keyCode);
     if (numPadKey != null) {
       return numPadKey;
     }
@@ -91,17 +90,17 @@ class RawKeyEventDataLinux extends RawKeyEventData {
     // autogenerated, since the label uniquely identifies an ID from the Unicode
     // plane.
     if (keyLabel != null &&
-        !LogicalKeyboardKey.isControlCharacter(keyLabel)) {
+        !LogicalKeyboardKey.isControlCharacter(keyLabel!)) {
       final int keyId = LogicalKeyboardKey.unicodePlane | (unicodeScalarValues & LogicalKeyboardKey.valueMask);
       return LogicalKeyboardKey.findKeyByKeyId(keyId) ?? LogicalKeyboardKey(
         keyId,
         keyLabel: keyLabel,
-        debugName: kReleaseMode ? null : 'Key ${keyLabel.toUpperCase()}',
+        debugName: kReleaseMode ? null : 'Key ${keyLabel!.toUpperCase()}',
       );
     }
 
     // Look to see if the keyCode is one we know about and have a mapping for.
-    LogicalKeyboardKey newKey = keyHelper.logicalKey(keyCode);
+    LogicalKeyboardKey? newKey = keyHelper.logicalKey(keyCode);
     if (newKey != null) {
       return newKey;
     }
@@ -158,13 +157,13 @@ abstract class KeyHelper {
 
   /// Returns true if the given [ModifierKey] was pressed at the time of this
   /// event.
-  bool isModifierPressed(ModifierKey key, int modifiers, {KeyboardSide side = KeyboardSide.any, int keyCode, bool isDown});
+  bool isModifierPressed(ModifierKey key, int modifiers, {KeyboardSide side = KeyboardSide.any, required int keyCode, required bool isDown});
 
   /// The numpad key from the specific key code mapping.
-  LogicalKeyboardKey numpadKey(int keyCode);
+  LogicalKeyboardKey? numpadKey(int keyCode);
 
   /// The logical key key from the specific key code mapping.
-  LogicalKeyboardKey logicalKey(int keyCode);
+  LogicalKeyboardKey? logicalKey(int keyCode);
 }
 
 /// Helper class that uses GLFW-specific key mappings.
@@ -212,7 +211,7 @@ class GLFWKeyHelper with KeyHelper {
   /// {@macro flutter.services.glfwKeyHelper.modifiers}
   static const int modifierNumericPad = 0x0020;
 
-  int _mergeModifiers({int modifiers, int keyCode, bool isDown}) {
+  int _mergeModifiers({required int modifiers, required int keyCode, required bool isDown}) {
     // GLFW Key codes for modifier keys.
     const int shiftLeftKeyCode = 340;
     const int shiftRightKeyCode = 344;
@@ -262,7 +261,7 @@ class GLFWKeyHelper with KeyHelper {
   }
 
   @override
-  bool isModifierPressed(ModifierKey key, int modifiers, {KeyboardSide side = KeyboardSide.any, int keyCode, bool isDown}) {
+  bool isModifierPressed(ModifierKey key, int modifiers, {KeyboardSide side = KeyboardSide.any, required int keyCode, required bool isDown}) {
     modifiers = _mergeModifiers(modifiers: modifiers, keyCode: keyCode, isDown: isDown);
     switch (key) {
       case ModifierKey.controlModifier:
@@ -283,7 +282,6 @@ class GLFWKeyHelper with KeyHelper {
         // These are not used in GLFW keyboards.
         return false;
     }
-    return false;
   }
 
   @override
@@ -303,17 +301,15 @@ class GLFWKeyHelper with KeyHelper {
       case ModifierKey.scrollLockModifier:
         return KeyboardSide.all;
     }
-    assert(false, 'Not handling $key type properly.');
-    return null;
   }
 
   @override
-  LogicalKeyboardKey numpadKey(int keyCode) {
+  LogicalKeyboardKey? numpadKey(int keyCode) {
     return kGlfwNumpadMap[keyCode];
   }
 
   @override
-  LogicalKeyboardKey logicalKey(int keyCode) {
+  LogicalKeyboardKey? logicalKey(int keyCode) {
     return kGlfwToLogicalKey[keyCode];
   }
 }
@@ -362,7 +358,7 @@ class GtkKeyHelper with KeyHelper {
   /// {@macro flutter.services.gtkKeyHelper.modifiers}
   static const int modifierMeta = 1 << 28;
 
-  int _mergeModifiers({int modifiers, int keyCode, bool isDown}) {
+  int _mergeModifiers({required int modifiers, required int keyCode, required bool isDown}) {
     // GTK Key codes for modifier keys.
     const int shiftLeftKeyCode = 0xffe1;
     const int shiftRightKeyCode = 0xffe2;
@@ -414,7 +410,7 @@ class GtkKeyHelper with KeyHelper {
   }
 
   @override
-  bool isModifierPressed(ModifierKey key, int modifiers, {KeyboardSide side = KeyboardSide.any, int keyCode, bool isDown}) {
+  bool isModifierPressed(ModifierKey key, int modifiers, {KeyboardSide side = KeyboardSide.any, required int keyCode, required bool isDown}) {
     modifiers = _mergeModifiers(modifiers: modifiers, keyCode: keyCode, isDown: isDown);
     switch (key) {
       case ModifierKey.controlModifier:
@@ -435,7 +431,6 @@ class GtkKeyHelper with KeyHelper {
         // These are not used in GTK keyboards.
         return false;
     }
-    return false;
   }
 
   @override
@@ -455,17 +450,15 @@ class GtkKeyHelper with KeyHelper {
       case ModifierKey.scrollLockModifier:
         return KeyboardSide.all;
     }
-    assert(false, 'Not handling $key type properly.');
-    return null;
   }
 
   @override
-  LogicalKeyboardKey numpadKey(int keyCode) {
+  LogicalKeyboardKey? numpadKey(int keyCode) {
     return kGtkNumpadMap[keyCode];
   }
 
   @override
-  LogicalKeyboardKey logicalKey(int keyCode) {
+  LogicalKeyboardKey? logicalKey(int keyCode) {
     return kGtkToLogicalKey[keyCode];
   }
 }

packages/flutter/lib/src/services/raw_keyboard_macos.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'package:flutter/foundation.dart';
 
@@ -63,7 +62,7 @@ class RawKeyEventDataMacOs extends RawKeyEventData {
   final int modifiers;
 
   @override
-  String get keyLabel => charactersIgnoringModifiers.isEmpty ? null : charactersIgnoringModifiers;
+  String? get keyLabel => charactersIgnoringModifiers.isEmpty ? null : charactersIgnoringModifiers;
 
   @override
   PhysicalKeyboardKey get physicalKey => kMacOsToPhysicalKey[keyCode] ?? PhysicalKeyboardKey.none;
@@ -73,7 +72,7 @@ class RawKeyEventDataMacOs extends RawKeyEventData {
     // Look to see if the keyCode is a printable number pad key, so that a
     // difference between regular keys (e.g. "=") and the number pad version
     // (e.g. the "=" on the number pad) can be determined.
-    final LogicalKeyboardKey numPadKey = kMacOsNumPadMap[keyCode];
+    final LogicalKeyboardKey? numPadKey = kMacOsNumPadMap[keyCode];
     if (numPadKey != null) {
       return numPadKey;
     }
@@ -81,8 +80,8 @@ class RawKeyEventDataMacOs extends RawKeyEventData {
     // Control keys such as ESC, CRTL, and SHIFT are not printable. HOME, DEL, arrow keys, and function
     // keys are considered modifier function keys, which generate invalid Unicode scalar values.
     if (keyLabel != null &&
-        !LogicalKeyboardKey.isControlCharacter(keyLabel) &&
-        !_isUnprintableKey(keyLabel)) {
+        !LogicalKeyboardKey.isControlCharacter(keyLabel!) &&
+        !_isUnprintableKey(keyLabel!)) {
       // Given that charactersIgnoringModifiers can contain a String of arbitrary length,
       // limit to a maximum of two Unicode scalar values. It is unlikely that a keyboard would produce a code point
       // bigger than 32 bits, but it is still worth defending against this case.
@@ -97,7 +96,7 @@ class RawKeyEventDataMacOs extends RawKeyEventData {
       return LogicalKeyboardKey.findKeyByKeyId(keyId) ?? LogicalKeyboardKey(
         keyId,
         keyLabel: keyLabel,
-        debugName: kReleaseMode ? null : 'Key ${keyLabel.toUpperCase()}',
+        debugName: kReleaseMode ? null : 'Key ${keyLabel!.toUpperCase()}',
       );
     }
 
@@ -145,7 +144,6 @@ class RawKeyEventDataMacOs extends RawKeyEventData {
       case KeyboardSide.right:
         return modifiers & rightMask != 0 || anyOnly;
     }
-    return false;
   }
 
   @override
@@ -185,8 +183,8 @@ class RawKeyEventDataMacOs extends RawKeyEventData {
   }
 
   @override
-  KeyboardSide getModifierSide(ModifierKey key) {
-    KeyboardSide findSide(int leftMask, int rightMask, int anyMask) {
+  KeyboardSide? getModifierSide(ModifierKey key) {
+    KeyboardSide? findSide(int leftMask, int rightMask, int anyMask) {
       final int combinedMask = leftMask | rightMask;
       final int combined = modifiers & combinedMask;
       if (combined == leftMask) {
@@ -218,9 +216,6 @@ class RawKeyEventDataMacOs extends RawKeyEventData {
       case ModifierKey.symbolModifier:
         return KeyboardSide.all;
     }
-
-    assert(false, 'Not handling $key type properly.');
-    return null;
   }
 
   /// Returns true if the given label represents an unprintable key.

packages/flutter/lib/src/services/raw_keyboard_web.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'package:flutter/foundation.dart';
 
@@ -21,8 +20,8 @@ class RawKeyEventDataWeb extends RawKeyEventData {
   ///
   /// The [code] and [metaState] arguments must not be null.
   const RawKeyEventDataWeb({
-    @required this.code,
-    @required this.key,
+    required this.code,
+    required this.key,
     this.metaState = modifierNone,
   })  : assert(code != null),
         assert(metaState != null);
@@ -69,13 +68,13 @@ class RawKeyEventDataWeb extends RawKeyEventData {
     // Look to see if the keyCode is a printable number pad key, so that a
     // difference between regular keys (e.g. ".") and the number pad version
     // (e.g. the "." on the number pad) can be determined.
-    final LogicalKeyboardKey numPadKey = kWebNumPadMap[code];
+    final LogicalKeyboardKey? numPadKey = kWebNumPadMap[code];
     if (numPadKey != null) {
       return numPadKey;
     }
 
     // Look to see if the [code] is one we know about and have a mapping for.
-    final LogicalKeyboardKey newKey = kWebToLogicalKey[code];
+    final LogicalKeyboardKey? newKey = kWebToLogicalKey[code];
     if (newKey != null) {
       return newKey;
     }

packages/flutter/lib/src/services/raw_keyboard_windows.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'package:flutter/foundation.dart';
 
@@ -55,7 +54,7 @@ class RawKeyEventDataWindows extends RawKeyEventData {
   final int modifiers;
 
   @override
-  String get keyLabel => characterCodePoint == 0 ? null : String.fromCharCode(characterCodePoint);
+  String? get keyLabel => characterCodePoint == 0 ? null : String.fromCharCode(characterCodePoint);
 
   @override
   PhysicalKeyboardKey get physicalKey => kWindowsToPhysicalKey[scanCode] ?? PhysicalKeyboardKey.none;
@@ -65,7 +64,7 @@ class RawKeyEventDataWindows extends RawKeyEventData {
     // Look to see if the keyCode is a printable number pad key, so that a
     // difference between regular keys (e.g. "=") and the number pad version
     // (e.g. the "=" on the number pad) can be determined.
-    final LogicalKeyboardKey numPadKey = kWindowsNumPadMap[keyCode];
+    final LogicalKeyboardKey? numPadKey = kWindowsNumPadMap[keyCode];
     if (numPadKey != null) {
       return numPadKey;
     }
@@ -74,16 +73,16 @@ class RawKeyEventDataWindows extends RawKeyEventData {
     // constant, or construct a new Unicode-based key from it. Don't mark it as
     // autogenerated, since the label uniquely identifies an ID from the Unicode
     // plane.
-    if (keyLabel != null && keyLabel.isNotEmpty && !LogicalKeyboardKey.isControlCharacter(keyLabel)) {
+    if (keyLabel != null && keyLabel!.isNotEmpty && !LogicalKeyboardKey.isControlCharacter(keyLabel!)) {
       final int keyId = LogicalKeyboardKey.unicodePlane | (characterCodePoint & LogicalKeyboardKey.valueMask);
       return LogicalKeyboardKey.findKeyByKeyId(keyId) ?? LogicalKeyboardKey(
         keyId,
         keyLabel: keyLabel,
-        debugName: kReleaseMode ? null : 'Key ${keyLabel.toUpperCase()}',
+        debugName: kReleaseMode ? null : 'Key ${keyLabel!.toUpperCase()}',
       );
     }
     // Look to see if the keyCode is one we know about and have a mapping for.
-    LogicalKeyboardKey newKey = kWindowsToLogicalKey[keyCode];
+    LogicalKeyboardKey? newKey = kWindowsToLogicalKey[keyCode];
     if (newKey != null) {
       return newKey;
     }
@@ -120,7 +119,6 @@ class RawKeyEventDataWindows extends RawKeyEventData {
       case KeyboardSide.right:
         return modifiers & rightMask != 0 || anyOnly;
     }
-    return false;
   }
 
   @override
@@ -162,8 +160,8 @@ class RawKeyEventDataWindows extends RawKeyEventData {
 
 
   @override
-  KeyboardSide getModifierSide(ModifierKey key) {
-    KeyboardSide findSide(int leftMask, int rightMask, int anyMask) {
+  KeyboardSide? getModifierSide(ModifierKey key) {
+    KeyboardSide? findSide(int leftMask, int rightMask, int anyMask) {
       final int combinedMask = leftMask | rightMask;
       final int combined = modifiers & combinedMask;
       if (combined == leftMask) {
@@ -197,9 +195,6 @@ class RawKeyEventDataWindows extends RawKeyEventData {
       case ModifierKey.symbolModifier:
         return KeyboardSide.all;
     }
-
-    assert(false, 'Not handling $key type properly.');
-    return null;
   }
 
   // These are not the values defined by the Windows header for each modifier. Since they

packages/flutter/lib/src/services/restoration.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 import 'dart:typed_data';
 
@@ -132,25 +130,25 @@ class RestorationManager extends ChangeNotifier {
   ///
   ///  * [RootRestorationScope], which makes the root bucket available in the
   ///    [Widget] tree.
-  Future<RestorationBucket> get rootBucket {
+  Future<RestorationBucket?> get rootBucket {
     if (!SystemChannels.restoration.checkMethodCallHandler(_methodHandler)) {
       SystemChannels.restoration.setMethodCallHandler(_methodHandler);
     }
     if (_rootBucketIsValid) {
-      return SynchronousFuture<RestorationBucket>(_rootBucket);
+      return SynchronousFuture<RestorationBucket?>(_rootBucket);
     }
     if (_pendingRootBucket == null) {
       _pendingRootBucket = Completer<RestorationBucket>();
       _getRootBucketFromEngine();
     }
-    return _pendingRootBucket.future;
+    return _pendingRootBucket!.future;
   }
-  RestorationBucket _rootBucket; // May be null to indicate that restoration is turned off.
-  Completer<RestorationBucket> _pendingRootBucket;
+  RestorationBucket? _rootBucket; // May be null to indicate that restoration is turned off.
+  Completer<RestorationBucket>? _pendingRootBucket;
   bool _rootBucketIsValid = false;
 
   Future<void> _getRootBucketFromEngine() async {
-    final Map<dynamic, dynamic> config = await SystemChannels.restoration.invokeMethod<Map<dynamic, dynamic>>('get');
+    final Map<dynamic, dynamic>? config = await SystemChannels.restoration.invokeMethod<Map<dynamic, dynamic>>('get');
     if (_pendingRootBucket == null) {
       // The restoration data was obtained via other means (e.g. by calling
       // [handleRestorationDataUpdate] while the request to the engine was
@@ -161,7 +159,7 @@ class RestorationManager extends ChangeNotifier {
     _parseAndHandleRestorationUpdateFromEngine(config);
   }
 
-  void _parseAndHandleRestorationUpdateFromEngine(Map<dynamic, dynamic> update) {
+  void _parseAndHandleRestorationUpdateFromEngine(Map<dynamic, dynamic>? update) {
     handleRestorationUpdateFromEngine(
       enabled: update != null && update['enabled'] as bool,
       data: update == null ? null : update['data'] as Uint8List,
@@ -185,16 +183,16 @@ class RestorationManager extends ChangeNotifier {
   /// accessed, [rootBucket] will complete synchronously the next time it is
   /// called.
   @protected
-  void handleRestorationUpdateFromEngine({@required bool enabled, @required Uint8List data}) {
+  void handleRestorationUpdateFromEngine({required bool enabled, required Uint8List? data}) {
     assert(enabled != null);
 
-    final RestorationBucket oldRoot = _rootBucket;
+    final RestorationBucket? oldRoot = _rootBucket;
 
     _rootBucket = enabled
         ? RestorationBucket.root(manager: this, rawData: _decodeRestorationData(data))
         : null;
     _rootBucketIsValid = true;
-    assert(_pendingRootBucket == null || !_pendingRootBucket.isCompleted);
+    assert(_pendingRootBucket == null || !_pendingRootBucket!.isCompleted);
     _pendingRootBucket?.complete(_rootBucket);
     _pendingRootBucket = null;
 
@@ -228,7 +226,7 @@ class RestorationManager extends ChangeNotifier {
     );
   }
 
-  Future<dynamic> _methodHandler(MethodCall call) {
+  Future<dynamic> _methodHandler(MethodCall call) async {
     switch (call.method) {
       case 'push':
         _parseAndHandleRestorationUpdateFromEngine(call.arguments as Map<dynamic, dynamic>);
@@ -236,10 +234,9 @@ class RestorationManager extends ChangeNotifier {
       default:
         throw UnimplementedError("${call.method} was invoked but isn't implemented by $runtimeType");
     }
-    return null;
   }
 
-  Map<dynamic, dynamic> _decodeRestorationData(Uint8List data) {
+  Map<dynamic, dynamic>? _decodeRestorationData(Uint8List? data) {
     if (data == null) {
       return null;
     }
@@ -248,7 +245,7 @@ class RestorationManager extends ChangeNotifier {
   }
 
   Uint8List _encodeRestorationData(Map<dynamic, dynamic> data) {
-    final ByteData encoded = const StandardMessageCodec().encodeMessage(data);
+    final ByteData encoded = const StandardMessageCodec().encodeMessage(data)!;
     return encoded.buffer.asUint8List(encoded.offsetInBytes, encoded.lengthInBytes);
   }
 
@@ -275,7 +272,7 @@ class RestorationManager extends ChangeNotifier {
     _bucketsNeedingSerialization.add(bucket);
     if (!_postFrameScheduled) {
       _postFrameScheduled = true;
-      SchedulerBinding.instance.addPostFrameCallback((Duration _) => _doSerialization());
+      SchedulerBinding.instance!.addPostFrameCallback((Duration _) => _doSerialization());
     }
   }
 
@@ -308,7 +305,7 @@ class RestorationManager extends ChangeNotifier {
       bucket.finalize();
     }
     _bucketsNeedingSerialization.clear();
-    sendToEngine(_encodeRestorationData(_rootBucket._rawData));
+    sendToEngine(_encodeRestorationData(_rootBucket!._rawData));
 
     assert(() {
       _debugDoingUpdate = false;
@@ -410,8 +407,8 @@ class RestorationBucket extends ChangeNotifier {
   ///
   /// The `restorationId` must not be null.
   RestorationBucket.empty({
-    @required String restorationId,
-    @required Object debugOwner,
+    required String restorationId,
+    required Object? debugOwner,
   }) : assert(restorationId != null),
        _restorationId = restorationId,
        _rawData = <String, dynamic>{} {
@@ -445,8 +442,8 @@ class RestorationBucket extends ChangeNotifier {
   ///
   /// The `manager` argument must not be null.
   RestorationBucket.root({
-    @required RestorationManager manager,
-    @required Map<dynamic, dynamic> rawData,
+    required RestorationManager manager,
+    required Map<dynamic, dynamic>? rawData,
   }) : assert(manager != null),
        _manager = manager,
        _rawData = rawData ?? <dynamic, dynamic>{},
@@ -468,9 +465,9 @@ class RestorationBucket extends ChangeNotifier {
   ///
   /// The `restorationId` and `parent` argument must not be null.
   RestorationBucket.child({
-    @required String restorationId,
-    @required RestorationBucket parent,
-    @required Object debugOwner,
+    required String restorationId,
+    required RestorationBucket parent,
+    required Object? debugOwner,
   }) : assert(restorationId != null),
        assert(parent != null),
        assert(parent._rawChildren[restorationId] != null),
@@ -494,14 +491,14 @@ class RestorationBucket extends ChangeNotifier {
   ///
   /// The value is used in error messages. Accessing the value is only valid
   /// in debug mode, otherwise it will return null.
-  Object get debugOwner {
+  Object? get debugOwner {
     assert(_debugAssertNotDisposed());
     return _debugOwner;
   }
-  Object _debugOwner;
+  Object? _debugOwner;
 
-  RestorationManager _manager;
-  RestorationBucket _parent;
+  RestorationManager? _manager;
+  RestorationBucket? _parent;
 
   /// The restoration ID under which the bucket is currently stored in the
   /// parent of this bucket (or wants to be stored if it is currently
@@ -545,7 +542,7 @@ class RestorationBucket extends ChangeNotifier {
   void decommission() {
     assert(_debugAssertNotDisposed());
     if (_parent != null) {
-      _parent._dropChild(this);
+      _parent!._dropChild(this);
       _parent = null;
     }
     _performDecommission();
@@ -678,7 +675,7 @@ class RestorationBucket extends ChangeNotifier {
   ///
   /// When the returned bucket is no longer needed, it must be [dispose]d to
   /// delete the information stored in it from the app's restoration data.
-  RestorationBucket claimChild(String restorationId, {@required Object debugOwner}) {
+  RestorationBucket claimChild(String restorationId, {required Object? debugOwner}) {
     assert(_debugAssertNotDisposed());
     assert(restorationId != null);
     // There are three cases to consider:
@@ -780,7 +777,7 @@ class RestorationBucket extends ChangeNotifier {
     bucket._visitChildren(_recursivelyUpdateManager);
   }
 
-  void _updateManager(RestorationManager newManager) {
+  void _updateManager(RestorationManager? newManager) {
     if (_manager == newManager) {
       return;
     }
@@ -811,7 +808,7 @@ class RestorationBucket extends ChangeNotifier {
         error.addAll(<DiagnosticsNode>[
           ErrorDescription(' * "$id" was claimed by:'),
           ...buckets.map((RestorationBucket bucket) => ErrorDescription('   * ${bucket.debugOwner}')),
-          ErrorDescription('   * ${_claimedChildren[id].debugOwner} (current owner)'),
+          ErrorDescription('   * ${_claimedChildren[id]!.debugOwner} (current owner)'),
         ]);
       }
       throw FlutterError.fromParts(error);
@@ -824,7 +821,7 @@ class RestorationBucket extends ChangeNotifier {
     assert(child._parent == this);
     if (_claimedChildren.remove(child.restorationId) == child) {
       _rawChildren.remove(child.restorationId);
-      final List<RestorationBucket> pendingChildren = _childrenToAdd[child.restorationId];
+      final List<RestorationBucket>? pendingChildren = _childrenToAdd[child.restorationId];
       if (pendingChildren != null) {
         final RestorationBucket toAdd = pendingChildren.removeLast();
         _finalizeAddChildData(toAdd);
@@ -893,9 +890,9 @@ class RestorationBucket extends ChangeNotifier {
     if (newRestorationId == restorationId) {
       return;
     }
-    _parent._removeChildData(this);
+    _parent!._removeChildData(this);
     _restorationId = newRestorationId;
-    _parent._addChildData(this);
+    _parent!._addChildData(this);
   }
 
   /// Deletes the bucket and all the data stored in it from the bucket
@@ -946,7 +943,7 @@ class RestorationBucket extends ChangeNotifier {
 ///
 /// Should only be called from within asserts. Always returns false outside
 /// of debug builds.
-bool debugIsSerializableForRestoration(Object object) {
+bool debugIsSerializableForRestoration(Object? object) {
   bool result = false;
 
   assert(() {

packages/flutter/lib/src/services/system_channels.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:ui';
 
@@ -218,7 +217,7 @@ class SystemChannels {
   ///
   ///  * [WidgetsBindingObserver.didChangeAppLifecycleState], which triggers
   ///    whenever a message is received on this channel.
-  static const BasicMessageChannel<String> lifecycle = BasicMessageChannel<String>(
+  static const BasicMessageChannel<String?> lifecycle = BasicMessageChannel<String?>(
       'flutter/lifecycle',
       StringCodec(),
   );

packages/flutter/lib/src/services/system_chrome.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 import 'dart:ui';
@@ -60,13 +59,13 @@ class ApplicationSwitcherDescription {
   const ApplicationSwitcherDescription({ this.label, this.primaryColor });
 
   /// A label and description of the current state of the application.
-  final String label;
+  final String? label;
 
   /// The application's primary color.
   ///
   /// This may influence the color that the operating system uses to represent
   /// the application.
-  final int primaryColor;
+  final int? primaryColor;
 }
 
 /// Specifies a system overlay at a particular location.
@@ -100,32 +99,32 @@ class SystemUiOverlayStyle {
   /// The color of the system bottom navigation bar.
   ///
   /// Only honored in Android versions O and greater.
-  final Color systemNavigationBarColor;
+  final Color? systemNavigationBarColor;
 
   /// The color of the divider between the system's bottom navigation bar and the app's content.
   ///
   /// Only honored in Android versions P and greater.
-  final Color systemNavigationBarDividerColor;
+  final Color? systemNavigationBarDividerColor;
 
   /// The brightness of the system navigation bar icons.
   ///
   /// Only honored in Android versions O and greater.
-  final Brightness systemNavigationBarIconBrightness;
+  final Brightness? systemNavigationBarIconBrightness;
 
   /// The color of top status bar.
   ///
   /// Only honored in Android version M and greater.
-  final Color statusBarColor;
+  final Color? statusBarColor;
 
   /// The brightness of top status bar.
   ///
   /// Only honored in iOS.
-  final Brightness statusBarBrightness;
+  final Brightness? statusBarBrightness;
 
   /// The brightness of the top status bar icons.
   ///
   /// Only honored in Android version M and greater.
-  final Brightness statusBarIconBrightness;
+  final Brightness? statusBarIconBrightness;
 
   /// System overlays should be drawn with a light color. Intended for
   /// applications with a dark background.
@@ -166,12 +165,12 @@ class SystemUiOverlayStyle {
 
   /// Creates a copy of this theme with the given fields replaced with new values.
   SystemUiOverlayStyle copyWith({
-    Color systemNavigationBarColor,
-    Color systemNavigationBarDividerColor,
-    Color statusBarColor,
-    Brightness statusBarBrightness,
-    Brightness statusBarIconBrightness,
-    Brightness systemNavigationBarIconBrightness,
+    Color? systemNavigationBarColor,
+    Color? systemNavigationBarDividerColor,
+    Color? statusBarColor,
+    Brightness? statusBarBrightness,
+    Brightness? statusBarIconBrightness,
+    Brightness? systemNavigationBarIconBrightness,
   }) {
     return SystemUiOverlayStyle(
       systemNavigationBarColor: systemNavigationBarColor ?? this.systemNavigationBarColor,
@@ -406,7 +405,7 @@ class SystemChrome {
       if (_pendingStyle != _latestStyle) {
         SystemChannels.platform.invokeMethod<void>(
           'SystemChrome.setSystemUIOverlayStyle',
-          _pendingStyle._toMap(),
+          _pendingStyle!._toMap(),
         );
         _latestStyle = _pendingStyle;
       }
@@ -414,10 +413,10 @@ class SystemChrome {
     });
   }
 
-  static SystemUiOverlayStyle _pendingStyle;
+  static SystemUiOverlayStyle? _pendingStyle;
 
   /// The last style that was set using [SystemChrome.setSystemUIOverlayStyle].
   @visibleForTesting
-  static SystemUiOverlayStyle get latestStyle => _latestStyle;
-  static SystemUiOverlayStyle _latestStyle;
+  static SystemUiOverlayStyle? get latestStyle => _latestStyle;
+  static SystemUiOverlayStyle? _latestStyle;
 }

packages/flutter/lib/src/services/system_navigator.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 
@@ -33,7 +32,7 @@ class SystemNavigator {
   /// This method should be preferred over calling `dart:io`'s [exit]
   /// method, as the latter may cause the underlying platform to act
   /// as if the application had crashed.
-  static Future<void> pop({bool animated}) async {
+  static Future<void> pop({bool? animated}) async {
     await SystemChannels.platform.invokeMethod<void>('SystemNavigator.pop', animated);
   }
 }

packages/flutter/lib/src/services/system_sound.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 

packages/flutter/lib/src/services/text_editing.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:ui' show hashValues, TextAffinity, TextPosition, TextRange;
 
@@ -17,8 +16,8 @@ class TextSelection extends TextRange {
   ///
   /// The [baseOffset] and [extentOffset] arguments must not be null.
   const TextSelection({
-    @required this.baseOffset,
-    @required this.extentOffset,
+    required this.baseOffset,
+    required this.extentOffset,
     this.affinity = TextAffinity.downstream,
     this.isDirectional = false,
   }) : super(
@@ -34,7 +33,7 @@ class TextSelection extends TextRange {
   ///
   /// The [offset] argument must not be null.
   const TextSelection.collapsed({
-    @required int offset,
+    required int offset,
     this.affinity = TextAffinity.downstream,
   }) : baseOffset = offset,
        extentOffset = offset,
@@ -121,10 +120,10 @@ class TextSelection extends TextRange {
   /// Creates a new [TextSelection] based on the current selection, with the
   /// provided parameters overridden.
   TextSelection copyWith({
-    int baseOffset,
-    int extentOffset,
-    TextAffinity affinity,
-    bool isDirectional,
+    int? baseOffset,
+    int? extentOffset,
+    TextAffinity? affinity,
+    bool? isDirectional,
   }) {
     return TextSelection(
       baseOffset: baseOffset ?? this.baseOffset,

packages/flutter/lib/src/services/text_formatter.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:math' as math;
 
@@ -103,7 +102,7 @@ class FilteringTextInputFormatter extends TextInputFormatter {
   /// must not be null.
   FilteringTextInputFormatter(
     this.filterPattern, {
-    @required this.allow,
+    required this.allow,
     this.replacementString = '',
   }) : assert(filterPattern != null),
        assert(allow != null),
@@ -342,7 +341,7 @@ class LengthLimitingTextInputFormatter extends TextInputFormatter {
   /// counted as a single character, but because it is a combination of two
   /// Unicode scalar values, '\u{1F44D}\u{1F3FD}', it is counted as two
   /// characters.
-  final int maxLength;
+  final int? maxLength;
 
   /// Truncate the given TextEditingValue to maxLength characters.
   ///
@@ -371,13 +370,13 @@ class LengthLimitingTextInputFormatter extends TextInputFormatter {
     TextEditingValue oldValue, // unused.
     TextEditingValue newValue,
   ) {
-    if (maxLength != null && maxLength > 0 && newValue.text.characters.length > maxLength) {
+    if (maxLength != null && maxLength! > 0 && newValue.text.characters.length > maxLength!) {
       // If already at the maximum and tried to enter even more, keep the old
       // value.
       if (oldValue.text.characters.length == maxLength) {
         return oldValue;
       }
-      return truncate(newValue, maxLength);
+      return truncate(newValue, maxLength!);
     }
     return newValue;
   }
@@ -390,7 +389,7 @@ TextEditingValue _selectionAwareTextManipulation(
   final int selectionStartIndex = value.selection.start;
   final int selectionEndIndex = value.selection.end;
   String manipulatedText;
-  TextSelection manipulatedSelection;
+  TextSelection? manipulatedSelection;
   if (selectionStartIndex < 0 || selectionEndIndex < 0) {
     manipulatedText = substringManipulation(value.text);
   } else {

packages/flutter/lib/src/services/text_input.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
 
 import 'dart:async';
 import 'dart:io' show Platform;
@@ -101,13 +100,13 @@ class TextInputType {
   ///
   /// This flag is only used for the [number] input type, otherwise `null`.
   /// Use `const TextInputType.numberWithOptions(signed: true)` to set this.
-  final bool signed;
+  final bool? signed;
 
   /// The number is decimal, allowing a decimal point to provide fractional.
   ///
   /// This flag is only used for the [number] input type, otherwise `null`.
   /// Use `const TextInputType.numberWithOptions(decimal: true)` to set this.
-  final bool decimal;
+  final bool? decimal;
 
   /// Optimize for textual information.
   ///
@@ -450,8 +449,8 @@ class TextInputConfiguration {
     this.inputType = TextInputType.text,
     this.obscureText = false,
     this.autocorrect = true,
-    SmartDashesType smartDashesType,
-    SmartQuotesType smartQuotesType,
+    SmartDashesType? smartDashesType,
+    SmartQuotesType? smartQuotesType,
     this.enableSuggestions = true,
     this.actionLabel,
     this.inputAction = TextInputAction.done,
@@ -487,7 +486,7 @@ class TextInputConfiguration {
   /// to the platform. This will prevent the corresponding input field from
   /// participating in autofills triggered by other fields. Additionally, on
   /// Android and web, setting [autofillConfiguration] to null disables autofill.
-  final AutofillConfiguration autofillConfiguration;
+  final AutofillConfiguration? autofillConfiguration;
 
   /// {@template flutter.services.textInput.smartDashesType}
   /// Whether to allow the platform to automatically format dashes.
@@ -555,7 +554,7 @@ class TextInputConfiguration {
   final bool enableSuggestions;
 
   /// What text to display in the text input control's action button.
-  final String actionLabel;
+  final String? actionLabel;
 
   /// What kind of action to request for the action button on the IME.
   final TextInputAction inputAction;
@@ -590,12 +589,12 @@ class TextInputConfiguration {
       'inputAction': inputAction.toString(),
       'textCapitalization': textCapitalization.toString(),
       'keyboardAppearance': keyboardAppearance.toString(),
-      if (autofillConfiguration != null) 'autofill': autofillConfiguration.toJson(),
+      if (autofillConfiguration != null) 'autofill': autofillConfiguration!.toJson(),
     };
   }
 }
 
-TextAffinity _toTextAffinity(String affinity) {
+TextAffinity? _toTextAffinity(String affinity) {
   switch (affinity) {
     case 'TextAffinity.downstream':
       return TextAffinity.downstream;
@@ -628,12 +627,12 @@ class RawFloatingCursorPoint {
   /// [FloatingCursorDragState.Update].
   RawFloatingCursorPoint({
     this.offset,
-    @required this.state,
+    required this.state,
   }) : assert(state != null),
        assert(state != FloatingCursorDragState.Update || offset != null);
 
   /// The raw position of the floating cursor as determined by the iOS sdk.
-  final Offset offset;
+  final Offset? offset;
 
   /// The state of the floating cursor.
   final FloatingCursorDragState state;
@@ -661,14 +660,14 @@ class TextEditingValue {
     return TextEditingValue(
       text: encoded['text'] as String,
       selection: TextSelection(
-        baseOffset: encoded['selectionBase'] as int ?? -1,
-        extentOffset: encoded['selectionExtent'] as int ?? -1,
+        baseOffset: encoded['selectionBase'] as int? ?? -1,
+        extentOffset: encoded['selectionExtent'] as int? ?? -1,
         affinity: _toTextAffinity(encoded['selectionAffinity'] as String) ?? TextAffinity.downstream,
-        isDirectional: encoded['selectionIsDirectional'] as bool ?? false,
+        isDirectional: encoded['selectionIsDirectional'] as bool? ?? false,
       ),
       composing: TextRange(
-        start: encoded['composingBase'] as int ?? -1,
-        end: encoded['composingExtent'] as int ?? -1,
+        start: encoded['composingBase'] as int? ?? -1,
+        end: encoded['composingExtent'] as int? ?? -1,
       ),
     );
   }
@@ -700,9 +699,9 @@ class TextEditingValue {
 
   /// Creates a copy of this value but with the given fields replaced with the new values.
   TextEditingValue copyWith({
-    String text,
-    TextSelection selection,
-    TextRange composing,
+    String? text,
+    TextSelection? selection,
+    TextRange? composing,
   }) {
     return TextEditingValue(
       text: text ?? this.text,
@@ -795,7 +794,7 @@ abstract class TextInputClient {
   ///
   /// * [AutofillGroup], a widget that creates an [AutofillScope] for its
   ///   descendent autofillable [TextInputClient]s.
-  AutofillScope get currentAutofillScope;
+  AutofillScope? get currentAutofillScope;
 
   /// Requests that this client update its editing state to the given value.
   void updateEditingValue(TextEditingValue value);
@@ -828,8 +827,8 @@ class TextInputConnection {
       : assert(_client != null),
         _id = _nextId++;
 
-  Size _cachedSize;
-  Matrix4 _cachedTransform;
+  Size? _cachedSize;
+  Matrix4? _cachedTransform;
 
   static int _nextId = 1;
   final int _id;
@@ -906,11 +905,11 @@ class TextInputConnection {
   /// of the hidden native input's content. Hence, the content size will match
   /// to the size of the editable widget's content.
   void setStyle({
-    @required String fontFamily,
-    @required double fontSize,
-    @required FontWeight fontWeight,
-    @required TextDirection textDirection,
-    @required TextAlign textAlign,
+    required String? fontFamily,
+    required double? fontSize,
+    required FontWeight? fontWeight,
+    required TextDirection textDirection,
+    required TextAlign textAlign,
   }) {
     assert(attached);
 
@@ -1108,10 +1107,10 @@ class TextInput {
     return true;
   }
 
-  MethodChannel _channel;
+  late MethodChannel _channel;
 
-  TextInputConnection _currentConnection;
-  TextInputConfiguration _currentConfiguration;
+  TextInputConnection? _currentConnection;
+  late TextInputConfiguration _currentConfiguration;
 
   Future<dynamic> _handleTextInputInvocation(MethodCall methodCall) async {
     if (_currentConnection == null)
@@ -1121,9 +1120,9 @@ class TextInput {
     // The requestExistingInputState request needs to be handled regardless of
     // the client ID, as long as we have a _currentConnection.
     if (method == 'TextInputClient.requestExistingInputState') {
-      assert(_currentConnection._client != null);
-      _attach(_currentConnection, _currentConfiguration);
-      final TextEditingValue editingValue = _currentConnection._client.currentTextEditingValue;
+      assert(_currentConnection!._client != null);
+      _attach(_currentConnection!, _currentConfiguration);
+      final TextEditingValue editingValue = _currentConnection!._client.currentTextEditingValue;
       if (editingValue != null) {
         _setEditingState(editingValue);
       }
@@ -1133,9 +1132,9 @@ class TextInput {
     final List<dynamic> args = methodCall.arguments as List<dynamic>;
 
     if (method == 'TextInputClient.updateEditingStateWithTag') {
-      final TextInputClient client = _currentConnection._client;
+      final TextInputClient client = _currentConnection!._client;
       assert(client != null);
-      final AutofillScope scope = client.currentAutofillScope;
+      final AutofillScope? scope = client.currentAutofillScope;
       final Map<String, dynamic> editingValue = args[1] as Map<String, dynamic>;
       for (final String tag in editingValue.keys) {
         final TextEditingValue textEditingValue = TextEditingValue.fromJSON(
@@ -1149,26 +1148,26 @@ class TextInput {
 
     final int client = args[0] as int;
     // The incoming message was for a different client.
-    if (client != _currentConnection._id)
+    if (client != _currentConnection!._id)
       return;
     switch (method) {
       case 'TextInputClient.updateEditingState':
-        _currentConnection._client.updateEditingValue(TextEditingValue.fromJSON(args[1] as Map<String, dynamic>));
+        _currentConnection!._client.updateEditingValue(TextEditingValue.fromJSON(args[1] as Map<String, dynamic>));
         break;
       case 'TextInputClient.performAction':
-        _currentConnection._client.performAction(_toTextInputAction(args[1] as String));
+        _currentConnection!._client.performAction(_toTextInputAction(args[1] as String));
         break;
       case 'TextInputClient.updateFloatingCursor':
-        _currentConnection._client.updateFloatingCursor(_toTextPoint(
+        _currentConnection!._client.updateFloatingCursor(_toTextPoint(
           _toTextCursorAction(args[1] as String),
           args[2] as Map<String, dynamic>,
         ));
         break;
       case 'TextInputClient.onConnectionClosed':
-        _currentConnection._client.connectionClosed();
+        _currentConnection!._client.connectionClosed();
         break;
       case 'TextInputClient.showAutocorrectionPromptRect':
-        _currentConnection._client.showAutocorrectionPromptRect(args[1] as int, args[2] as int);
+        _currentConnection!._client.showAutocorrectionPromptRect(args[1] as int, args[2] as int);
         break;
       default:
         throw MissingPluginException();