Migrated some services and widgets doc comments to null safety. (#72792)

dev/tools/gen_keycodes/data/keyboard_key.tmpl

@@ -58,7 +58,7 @@ abstract class KeyboardKey with Diagnosticable {
 /// // The node used to request the keyboard focus.
 /// final FocusNode _focusNode = FocusNode();
 /// // The message to display.
-/// String _message;
+/// String? _message;
 ///
 /// // Focus nodes need to be disposed.
 /// @override
@@ -75,7 +75,7 @@ abstract class KeyboardKey with Diagnosticable {
 ///       _message = 'Pressed the "Q" key!';
 ///     } else {
 ///       if (kReleaseMode) {
-///         _message = 'Not a Q: Key label is "${event.logicalKey.keyLabel ?? '<none>'}"';
+///         _message = 'Not a Q: Key label is "${event.logicalKey.keyLabel}"';
 ///       } else {
 ///         // This will only print useful information in debug mode.
 ///         _message = 'Not a Q: Pressed ${event.logicalKey.debugName}';
@@ -91,13 +91,13 @@ abstract class KeyboardKey with Diagnosticable {
 ///     color: Colors.white,
 ///     alignment: Alignment.center,
 ///     child: DefaultTextStyle(
-///       style: textTheme.headline4,
+///       style: textTheme.headline4!,
 ///       child: RawKeyboardListener(
 ///         focusNode: _focusNode,
 ///         onKey: _handleKeyEvent,
 ///         child: AnimatedBuilder(
 ///           animation: _focusNode,
-///           builder: (BuildContext context, Widget child) {
+///           builder: (BuildContext context, Widget? child) {
 ///             if (!_focusNode.hasFocus) {
 ///               return GestureDetector(
 ///                 onTap: () {
@@ -346,7 +346,7 @@ class LogicalKeyboardKey extends KeyboardKey {
 /// // The node used to request the keyboard focus.
 /// final FocusNode _focusNode = FocusNode();
 /// // The message to display.
-/// String _message;
+/// String? _message;
 ///
 /// // Focus nodes need to be disposed.
 /// @override
@@ -374,13 +374,13 @@ class LogicalKeyboardKey extends KeyboardKey {
 ///     color: Colors.white,
 ///     alignment: Alignment.center,
 ///     child: DefaultTextStyle(
-///       style: textTheme.headline4,
+///       style: textTheme.headline4!,
 ///       child: RawKeyboardListener(
 ///         focusNode: _focusNode,
 ///         onKey: _handleKeyEvent,
 ///         child: AnimatedBuilder(
 ///           animation: _focusNode,
-///           builder: (BuildContext context, Widget child) {
+///           builder: (BuildContext context, Widget? child) {
 ///             if (!_focusNode.hasFocus) {
 ///               return GestureDetector(
 ///                 onTap: () {

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

@@ -45,7 +45,7 @@ abstract class KeyboardKey with Diagnosticable {
 /// look at the physical key to make sure that regardless of the character the
 /// key produces, you got the key that is in that location on the keyboard.
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold}
 /// This example shows how to detect if the user has selected the logical "Q"
 /// key.
 ///
@@ -58,7 +58,7 @@ abstract class KeyboardKey with Diagnosticable {
 /// // The node used to request the keyboard focus.
 /// final FocusNode _focusNode = FocusNode();
 /// // The message to display.
-/// String _message;
+/// String? _message;
 ///
 /// // Focus nodes need to be disposed.
 /// @override
@@ -75,7 +75,7 @@ abstract class KeyboardKey with Diagnosticable {
 ///       _message = 'Pressed the "Q" key!';
 ///     } else {
 ///       if (kReleaseMode) {
-///         _message = 'Not a Q: Key label is "${event.logicalKey.keyLabel ?? '<none>'}"';
+///         _message = 'Not a Q: Key label is "${event.logicalKey.keyLabel}"';
 ///       } else {
 ///         // This will only print useful information in debug mode.
 ///         _message = 'Not a Q: Pressed ${event.logicalKey.debugName}';
@@ -91,13 +91,13 @@ abstract class KeyboardKey with Diagnosticable {
 ///     color: Colors.white,
 ///     alignment: Alignment.center,
 ///     child: DefaultTextStyle(
-///       style: textTheme.headline4,
+///       style: textTheme.headline4!,
 ///       child: RawKeyboardListener(
 ///         focusNode: _focusNode,
 ///         onKey: _handleKeyEvent,
 ///         child: AnimatedBuilder(
 ///           animation: _focusNode,
-///           builder: (BuildContext context, Widget child) {
+///           builder: (BuildContext context, Widget? child) {
 ///             if (!_focusNode.hasFocus) {
 ///               return GestureDetector(
 ///                 onTap: () {
@@ -1987,7 +1987,7 @@ class LogicalKeyboardKey extends KeyboardKey {
 /// looking for "the key next next to the TAB key", since on a French keyboard,
 /// the key next to the TAB key has an "A" on it.
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold}
 /// This example shows how to detect if the user has selected the physical key
 /// to the right of the CAPS LOCK key.
 ///
@@ -1999,7 +1999,7 @@ class LogicalKeyboardKey extends KeyboardKey {
 /// // The node used to request the keyboard focus.
 /// final FocusNode _focusNode = FocusNode();
 /// // The message to display.
-/// String _message;
+/// String? _message;
 ///
 /// // Focus nodes need to be disposed.
 /// @override
@@ -2027,13 +2027,13 @@ class LogicalKeyboardKey extends KeyboardKey {
 ///     color: Colors.white,
 ///     alignment: Alignment.center,
 ///     child: DefaultTextStyle(
-///       style: textTheme.headline4,
+///       style: textTheme.headline4!,
 ///       child: RawKeyboardListener(
 ///         focusNode: _focusNode,
 ///         onKey: _handleKeyEvent,
 ///         child: AnimatedBuilder(
 ///           animation: _focusNode,
-///           builder: (BuildContext context, Widget child) {
+///           builder: (BuildContext context, Widget? child) {
 ///             if (!_focusNode.hasFocus) {
 ///               return GestureDetector(
 ///                 onTap: () {

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

@@ -12,9 +12,6 @@ import 'binding.dart';
 import 'message_codec.dart';
 import 'message_codecs.dart';
 
-// Examples can assume:
-// // @dart = 2.9
-
 /// A named channel for communicating with platform plugins using asynchronous
 /// message passing.
 ///
@@ -196,9 +193,9 @@ class MethodChannel {
   ///   static const MethodChannel _channel = MethodChannel('music');
   ///
   ///   static Future<bool> isLicensed() async {
-  ///     // invokeMethod returns a Future<T> which can be inferred as bool
-  ///     // in this context.
-  ///     return _channel.invokeMethod('isLicensed');
+  ///     // invokeMethod returns a Future<T?>, so we handle the case where
+  ///     // the return value is null by treating null as false.
+  ///     return _channel.invokeMethod<bool>('isLicensed').then<bool>((bool? value) => value ?? false);
   ///   }
   ///
   ///   static Future<List<Song>> songs() async {

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

@@ -344,7 +344,7 @@ class SystemChrome {
   /// navigation bar and synthesize them into a single style. This can be used
   /// to configure the system styles when an app bar is not used.
   ///
-  /// {@tool sample --template=stateful_widget_material_no_null_safety}
+  /// {@tool sample --template=stateful_widget_material}
   /// The following example creates a widget that changes the status bar color
   /// to a random value on Android.
   ///

packages/flutter/lib/src/widgets/animated_cross_fade.dart

@@ -11,8 +11,7 @@ import 'ticker_provider.dart';
 import 'transitions.dart';
 
 // Examples can assume:
-// // @dart = 2.9
-// bool _first;
+// bool _first = false;
 
 /// Specifies which of two children to show. See [AnimatedCrossFade].
 ///

packages/flutter/lib/src/widgets/gesture_detector.dart

@@ -48,11 +48,10 @@ export 'package:flutter/gestures.dart' show
 export 'package:flutter/rendering.dart' show RenderSemanticsGestureHandler;
 
 // Examples can assume:
-// // @dart = 2.9
-// bool _lights;
+// late bool _lights;
 // void setState(VoidCallback fn) { }
-// String _last;
-// Color _color;
+// late String _last;
+// late Color _color;
 
 /// Factory for creating gesture recognizers.
 ///
@@ -1045,8 +1044,8 @@ class RawGestureDetector extends StatefulWidget {
   /// ```dart
   /// class ForcePressGestureDetectorWithSemantics extends StatelessWidget {
   ///   const ForcePressGestureDetectorWithSemantics({
-  ///     this.child,
-  ///     this.onForcePress,
+  ///     required this.child,
+  ///     required this.onForcePress,
   ///   });
   ///
   ///   final Widget child;

packages/flutter/lib/src/widgets/image.dart

@@ -762,7 +762,7 @@ class Image extends StatefulWidget {
   /// ```
   /// {@endtemplate}
   ///
-  /// {@tool dartpad --template=stateless_widget_material_no_null_safety}
+  /// {@tool dartpad --template=stateless_widget_material}
   ///
   /// The following sample demonstrates how to use this builder to implement an
   /// image that fades in once it's been loaded.
@@ -781,8 +781,8 @@ class Image extends StatefulWidget {
   ///     ),
   ///     child: Image.network(
   ///       'https://flutter.github.io/assets-for-api-docs/assets/widgets/puffin.jpg',
-  ///       frameBuilder: (BuildContext context, Widget child, int frame, bool wasSynchronouslyLoaded) {
-  ///         if (wasSynchronouslyLoaded) {
+  ///       frameBuilder: (BuildContext context, Widget child, int? frame, bool? wasSynchronouslyLoaded) {
+  ///         if (wasSynchronouslyLoaded ?? false) {
   ///           return child;
   ///         }
   ///         return AnimatedOpacity(
@@ -828,7 +828,7 @@ class Image extends StatefulWidget {
   ///
   /// {@macro flutter.widgets.Image.frameBuilder.chainedBuildersExample}
   ///
-  /// {@tool dartpad --template=stateless_widget_material_no_null_safety}
+  /// {@tool dartpad --template=stateless_widget_material}
   ///
   /// The following sample uses [loadingBuilder] to show a
   /// [CircularProgressIndicator] while an image loads over the network.
@@ -843,13 +843,13 @@ class Image extends StatefulWidget {
   ///     ),
   ///     child: Image.network(
   ///       'https://example.com/image.jpg',
-  ///       loadingBuilder: (BuildContext context, Widget child, ImageChunkEvent loadingProgress) {
+  ///       loadingBuilder: (BuildContext context, Widget child, ImageChunkEvent? loadingProgress) {
   ///         if (loadingProgress == null)
   ///           return child;
   ///         return Center(
   ///           child: CircularProgressIndicator(
   ///             value: loadingProgress.expectedTotalBytes != null
-  ///                 ? loadingProgress.cumulativeBytesLoaded / loadingProgress.expectedTotalBytes
+  ///                 ? loadingProgress.cumulativeBytesLoaded / loadingProgress.expectedTotalBytes!
   ///                 : null,
   ///           ),
   ///         );
@@ -873,7 +873,7 @@ class Image extends StatefulWidget {
   /// [FlutterError.onError]. If it is provided, the caller should either handle
   /// the exception by providing a replacement widget, or rethrow the exception.
   ///
-  /// {@tool dartpad --template=stateless_widget_material_no_null_safety}
+  /// {@tool dartpad --template=stateless_widget_material}
   ///
   /// The following sample uses [errorBuilder] to show a '😢' in place of the
   /// image that fails to load, and prints the error to the console.
@@ -888,7 +888,7 @@ class Image extends StatefulWidget {
   ///     ),
   ///     child: Image.network(
   ///       'https://example.does.not.exist/image.jpg',
-  ///       errorBuilder: (BuildContext context, Object exception, StackTrace stackTrace) {
+  ///       errorBuilder: (BuildContext context, Object exception, StackTrace? stackTrace) {
   ///         // Appropriate logging or analytics, e.g.
   ///         // myAnalytics.recordError(
   ///         //   'An error occurred loading "https://example.does.not.exist/image.jpg"',

packages/flutter/lib/src/widgets/implicit_animations.dart

@@ -19,7 +19,6 @@ import 'ticker_provider.dart';
 import 'transitions.dart';
 
 // Examples can assume:
-// // @dart = 2.9
 // class MyWidget extends ImplicitlyAnimatedWidget {
 //   MyWidget() : super(duration: const Duration(seconds: 1));
 //   final Color targetColor = Colors.black;
@@ -480,14 +479,14 @@ abstract class ImplicitlyAnimatedWidgetState<T extends ImplicitlyAnimatedWidget>
   ///
   /// ```dart
   /// class MyWidgetState extends AnimatedWidgetBaseState<MyWidget> {
-  ///   ColorTween _colorTween;
+  ///   ColorTween? _colorTween;
   ///
   ///   @override
   ///   Widget build(BuildContext context) {
   ///     return Text(
   ///       'Hello World',
   ///       // Computes the value of the text color at any given time.
-  ///       style: TextStyle(color: _colorTween.evaluate(animation)),
+  ///       style: TextStyle(color: _colorTween?.evaluate(animation)),
   ///     );
   ///   }
   ///
@@ -502,7 +501,7 @@ abstract class ImplicitlyAnimatedWidgetState<T extends ImplicitlyAnimatedWidget>
   ///       // A function that takes a color value and returns a tween
   ///       // beginning at that value.
   ///       (value) => ColorTween(begin: value),
-  ///     );
+  ///     ) as ColorTween?;
   ///
   ///     // We could have more tweens than one by using the visitor
   ///     // multiple times.
@@ -573,7 +572,7 @@ abstract class AnimatedWidgetBaseState<T extends ImplicitlyAnimatedWidget> exten
 ///
 /// {@youtube 560 315 https://www.youtube.com/watch?v=yI-8QHpGIP4}
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold}
 ///
 /// The following example (depicted above) transitions an AnimatedContainer
 /// between two states. It adjusts the `height`, `width`, `color`, and
@@ -812,7 +811,7 @@ class _AnimatedContainerState extends AnimatedWidgetBaseState<AnimatedContainer>
 /// of [Curves.fastOutSlowIn].
 /// {@animation 250 266 https://flutter.github.io/assets-for-api-docs/assets/widgets/animated_padding.mp4}
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold}
 ///
 /// The following code implements the [AnimatedPadding] widget, using a [curve] of
 /// [Curves.easeInOut].
@@ -933,7 +932,7 @@ class _AnimatedPaddingState extends AnimatedWidgetBaseState<AnimatedPadding> {
 /// it also requires more development overhead as you have to manually manage
 /// the lifecycle of the underlying [AnimationController].
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold}
 ///
 /// The following code implements the [AnimatedAlign] widget, using a [curve] of
 /// [Curves.fastOutSlowIn].
@@ -1098,7 +1097,7 @@ class _AnimatedAlignState extends AnimatedWidgetBaseState<AnimatedAlign> {
 /// it also requires more development overhead as you have to manually manage
 /// the lifecycle of the underlying [AnimationController].
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_center_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold_center}
 ///
 /// The following example transitions an AnimatedPositioned
 /// between two states. It adjusts the `height`, `width`, and
@@ -1550,7 +1549,7 @@ class _AnimatedOpacityState extends ImplicitlyAnimatedWidgetState<AnimatedOpacit
 /// Here's an illustration of what using this widget looks like, using a [curve]
 /// of [Curves.fastOutSlowIn].
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_center_freeform_state_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold_center_freeform_state}
 /// Creates a [CustomScrollView] with a [SliverFixedExtentList] and a
 /// [FloatingActionButton]. Pressing the button animates the lists' opacity.
 ///

packages/flutter/lib/src/widgets/restoration_properties.dart

@@ -10,9 +10,6 @@ import 'package:flutter/services.dart';
 import 'editable_text.dart';
 import 'restoration.dart';
 
-// Examples can assume:
-// // @dart = 2.9
-
 /// A [RestorableProperty] that makes the wrapped value accessible to the owning
 /// [State] object via the [value] getter and setter.
 ///
@@ -22,7 +19,7 @@ import 'restoration.dart';
 ///
 /// ## Using a RestorableValue
 ///
-/// {@tool dartpad --template=stateful_widget_restoration_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_restoration}
 /// A [StatefulWidget] that has a restorable [int] property.
 ///
 /// ```dart
@@ -33,7 +30,7 @@ import 'restoration.dart';
 ///   RestorableInt _answer = RestorableInt(42);
 ///
 ///   @override
-///   void restoreState(RestorationBucket oldBucket, bool initialRestore) {
+///   void restoreState(RestorationBucket? oldBucket, bool initialRestore) {
 ///     // All restorable properties must be registered with the mixin. After
 ///     // registration, the answer either has its old value restored or is
 ///     // initialized to its default value.
@@ -77,14 +74,17 @@ import 'restoration.dart';
 ///   Duration createDefaultValue() => const Duration();
 ///
 ///   @override
-///   void didUpdateValue(Duration oldValue) {
-///     if (oldValue.inMicroseconds != value.inMicroseconds)
+///   void didUpdateValue(Duration? oldValue) {
+///     if (oldValue == null || oldValue.inMicroseconds != value.inMicroseconds)
 ///       notifyListeners();
 ///   }
 ///
 ///   @override
-///   Duration fromPrimitives(Object data) {
-///     return Duration(microseconds: data as int);
+///   Duration fromPrimitives(Object? data) {
+///     if (data != null) {
+///       return Duration(microseconds: data as int);
+///     }
+///     return const Duration();
 ///   }
 ///
 ///   @override

packages/flutter/lib/src/widgets/routes.dart

@@ -24,9 +24,8 @@ import 'scroll_controller.dart';
 import 'transitions.dart';
 
 // Examples can assume:
-// // @dart = 2.9
 // dynamic routeObserver;
-// NavigatorState navigator;
+// late NavigatorState navigator;
 
 /// A route that displays widgets in the [Navigator]'s [Overlay].
 abstract class OverlayRoute<T> extends Route<T> {
@@ -541,7 +540,7 @@ mixin LocalHistoryRoute<T> on Route<T> {
   ///     // rectangle. When this local history entry is removed, we hide the red
   ///     // rectangle.
   ///     setState(() => _showRectangle = true);
-  ///     ModalRoute.of(context).addLocalHistoryEntry(
+  ///     ModalRoute.of(context)?.addLocalHistoryEntry(
   ///         LocalHistoryEntry(
   ///             onRemove: () {
   ///               // Hide the red rectangle.

packages/flutter/lib/src/widgets/text.dart

@@ -13,8 +13,7 @@ import 'inherited_theme.dart';
 import 'media_query.dart';
 
 // Examples can assume:
-// // @dart = 2.9
-// String _name;
+// late String _name;
 
 /// The text style to apply to descendant [Text] widgets which don't have an
 /// explicit style.