migrate gestures to nullsafety (#62157)

dev/tools/dartdoc.dart

@@ -126,6 +126,7 @@ Future<void> main(List<String> arguments) async {
   final List<String> dartdocArgs = <String>[
     ...dartdocBaseArgs,
     '--allow-tools',
+    '--enable-experiment=non-nullable',
     if (args['json'] as bool) '--json',
     if (args['validate-links'] as bool) '--validate-links' else '--no-validate-links',
     '--link-to-source-excludes', '../../bin/cache',

packages/flutter/lib/gestures.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
-
 /// The Flutter gesture recognizers.
 ///
 /// To use, import `package:flutter/gestures.dart`.

packages/flutter/lib/src/gestures/arena.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';
 
@@ -65,7 +64,7 @@ class _GestureArena {
   /// "eager winner". We look for an eager winner when closing the arena to new
   /// participants, and if there is one, we resolve the arena in its favor at
   /// that time.
-  GestureArenaMember eagerWinner;
+  GestureArenaMember? eagerWinner;
 
   void add(GestureArenaMember member) {
     assert(isOpen);
@@ -119,7 +118,7 @@ class GestureArenaManager {
   ///
   /// Called after the framework has finished dispatching the pointer down event.
   void close(int pointer) {
-    final _GestureArena state = _arenas[pointer];
+    final _GestureArena? state = _arenas[pointer];
     if (state == null)
       return; // This arena either never existed or has been resolved.
     state.isOpen = false;
@@ -141,7 +140,7 @@ class GestureArenaManager {
   ///  * [hold]
   ///  * [release]
   void sweep(int pointer) {
-    final _GestureArena state = _arenas[pointer];
+    final _GestureArena? state = _arenas[pointer];
     if (state == null)
       return; // This arena either never existed or has been resolved.
     assert(!state.isOpen);
@@ -175,7 +174,7 @@ class GestureArenaManager {
   ///  * [sweep]
   ///  * [release]
   void hold(int pointer) {
-    final _GestureArena state = _arenas[pointer];
+    final _GestureArena? state = _arenas[pointer];
     if (state == null)
       return; // This arena either never existed or has been resolved.
     state.isHeld = true;
@@ -192,7 +191,7 @@ class GestureArenaManager {
   ///  * [sweep]
   ///  * [hold]
   void release(int pointer) {
-    final _GestureArena state = _arenas[pointer];
+    final _GestureArena? state = _arenas[pointer];
     if (state == null)
       return; // This arena either never existed or has been resolved.
     state.isHeld = false;
@@ -205,7 +204,7 @@ class GestureArenaManager {
   ///
   /// This is called by calling [GestureArenaEntry.resolve] on the object returned from [add].
   void _resolve(int pointer, GestureArenaMember member, GestureDisposition disposition) {
-    final _GestureArena state = _arenas[pointer];
+    final _GestureArena? state = _arenas[pointer];
     if (state == null)
       return; // This arena has already resolved.
     assert(_debugLogDiagnostic(pointer, '${ disposition == GestureDisposition.accepted ? "Accepting" : "Rejecting" }: $member'));
@@ -236,7 +235,7 @@ class GestureArenaManager {
       assert(_debugLogDiagnostic(pointer, 'Arena empty.'));
     } else if (state.eagerWinner != null) {
       assert(_debugLogDiagnostic(pointer, 'Eager winner: ${state.eagerWinner}'));
-      _resolveInFavorOf(pointer, state, state.eagerWinner);
+      _resolveInFavorOf(pointer, state, state.eagerWinner!);
     }
   }
 
@@ -265,10 +264,10 @@ class GestureArenaManager {
     member.acceptGesture(pointer);
   }
 
-  bool _debugLogDiagnostic(int pointer, String message, [ _GestureArena state ]) {
+  bool _debugLogDiagnostic(int pointer, String message, [ _GestureArena? state ]) {
     assert(() {
       if (debugPrintGestureArenaDiagnostics) {
-        final int count = state != null ? state.members.length : null;
+        final int? count = state != null ? state.members.length : null;
         final String s = count != 1 ? 's' : '';
         debugPrint('Gesture arena ${pointer.toString().padRight(4)} ❙ $message${ count != null ? " with $count member$s." : ""}');
       }

packages/flutter/lib/src/gestures/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:collection';
@@ -75,8 +74,8 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
   }
 
   /// The singleton instance of this object.
-  static GestureBinding get instance => _instance;
-  static GestureBinding _instance;
+  static GestureBinding? get instance => _instance;
+  static GestureBinding? _instance;
 
   final Queue<PointerEvent> _pendingPointerEvents = Queue<PointerEvent>();
 
@@ -123,7 +122,7 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
 
   void _handlePointerEvent(PointerEvent event) {
     assert(!locked);
-    HitTestResult hitTestResult;
+    HitTestResult? hitTestResult;
     if (event is PointerDownEvent || event is PointerSignalEvent) {
       assert(!_hitTests.containsKey(event.pointer));
       hitTestResult = HitTestResult();
@@ -172,7 +171,7 @@ mixin GestureBinding on BindingBase implements HitTestable, HitTestDispatcher, H
   /// might throw. The [hitTestResult] argument may only be null for
   /// [PointerHoverEvent], [PointerAddedEvent], or [PointerRemovedEvent] events.
   @override // from HitTestDispatcher
-  void dispatchEvent(PointerEvent event, HitTestResult hitTestResult) {
+  void dispatchEvent(PointerEvent event, HitTestResult? hitTestResult) {
     assert(!locked);
     // No hit test information implies that this is a hover or pointer
     // add/remove event.
@@ -243,12 +242,12 @@ class FlutterErrorDetailsForPointerEventDispatcher extends FlutterErrorDetails {
   /// that will subsequently be reported using [FlutterError.onError].
   const FlutterErrorDetailsForPointerEventDispatcher({
     dynamic exception,
-    StackTrace stack,
-    String library,
-    DiagnosticsNode context,
+    StackTrace? stack,
+    String? library,
+    DiagnosticsNode? context,
     this.event,
     this.hitTestEntry,
-    InformationCollector informationCollector,
+    InformationCollector? informationCollector,
     bool silent = false,
   }) : super(
     exception: exception,
@@ -260,7 +259,7 @@ class FlutterErrorDetailsForPointerEventDispatcher extends FlutterErrorDetails {
   );
 
   /// The pointer event that was being routed when the exception was raised.
-  final PointerEvent event;
+  final PointerEvent? event;
 
   /// The hit test result entry for the object whose handleEvent method threw
   /// the exception. May be null if no hit test entry is associated with the
@@ -268,5 +267,5 @@ class FlutterErrorDetailsForPointerEventDispatcher extends FlutterErrorDetails {
   ///
   /// The target object itself is given by the [HitTestEntry.target] property of
   /// the hitTestEntry object.
-  final HitTestEntry hitTestEntry;
+  final HitTestEntry? hitTestEntry;
 }

packages/flutter/lib/src/gestures/constants.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
 
 // Modeled after Android's ViewConfiguration:
 // https://github.com/android/platform_frameworks_base/blob/master/core/java/android/view/ViewConfiguration.java

packages/flutter/lib/src/gestures/converter.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' as ui show PointerData, PointerChange, PointerSignalKind;
 
@@ -214,7 +213,7 @@ class PointerEventConverter {
             break;
         }
       } else {
-        switch (datum.signalKind) {
+        switch (datum.signalKind!) {
           case ui.PointerSignalKind.scroll:
             final Offset scrollDelta =
                 Offset(datum.scrollDeltaX, datum.scrollDeltaY) / devicePixelRatio;
@@ -238,6 +237,5 @@ class PointerEventConverter {
     }
   }
 
-  static double _toLogicalPixels(double physicalPixels, double devicePixelRatio) =>
-      physicalPixels == null ? null : physicalPixels / devicePixelRatio;
+  static double _toLogicalPixels(double physicalPixels, double devicePixelRatio) => physicalPixels / devicePixelRatio;
 }

packages/flutter/lib/src/gestures/debug.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';
 

packages/flutter/lib/src/gestures/drag.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 'drag_details.dart';
 

packages/flutter/lib/src/gestures/drag_details.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 Offset;
 
@@ -24,7 +23,7 @@ class DragDownDetails {
   /// The [globalPosition] argument must not be null.
   DragDownDetails({
     this.globalPosition = Offset.zero,
-    Offset localPosition,
+    Offset? localPosition,
   }) : assert(globalPosition != null),
        localPosition = localPosition ?? globalPosition;
 
@@ -71,7 +70,7 @@ class DragStartDetails {
   DragStartDetails({
     this.sourceTimeStamp,
     this.globalPosition = Offset.zero,
-    Offset localPosition,
+    Offset? localPosition,
   }) : assert(globalPosition != null),
        localPosition = localPosition ?? globalPosition;
 
@@ -79,7 +78,7 @@ class DragStartDetails {
   /// event.
   ///
   /// Could be null if triggered from proxied events such as accessibility.
-  final Duration sourceTimeStamp;
+  final Duration? sourceTimeStamp;
 
   /// The global position at which the pointer contacted the screen.
   ///
@@ -134,8 +133,8 @@ class DragUpdateDetails {
     this.sourceTimeStamp,
     this.delta = Offset.zero,
     this.primaryDelta,
-    @required this.globalPosition,
-    Offset localPosition,
+    required this.globalPosition,
+    Offset? localPosition,
   }) : assert(delta != null),
        assert(primaryDelta == null
            || (primaryDelta == delta.dx && delta.dy == 0.0)
@@ -146,7 +145,7 @@ class DragUpdateDetails {
   /// event.
   ///
   /// Could be null if triggered from proxied events such as accessibility.
-  final Duration sourceTimeStamp;
+  final Duration? sourceTimeStamp;
 
   /// The amount the pointer has moved in the coordinate space of the event
   /// receiver since the previous update.
@@ -169,7 +168,7 @@ class DragUpdateDetails {
   /// two-dimensional drag (e.g., a pan), then this value is null.
   ///
   /// Defaults to null if not specified in the constructor.
-  final double primaryDelta;
+  final double? primaryDelta;
 
   /// The pointer's global position when it triggered this update.
   ///
@@ -233,7 +232,7 @@ class DragEndDetails {
   /// two-dimensional drag (e.g., a pan), then this value is null.
   ///
   /// Defaults to null if not specified in the constructor.
-  final double primaryVelocity;
+  final double? primaryVelocity;
 
   @override
   String toString() => '${objectRuntimeType(this, 'DragEndDetails')}($velocity)';

packages/flutter/lib/src/gestures/eager.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 'arena.dart';
 import 'events.dart';
@@ -17,7 +16,7 @@ class EagerGestureRecognizer extends OneSequenceGestureRecognizer {
   /// Create an eager gesture recognizer.
   ///
   /// {@macro flutter.gestures.gestureRecognizer.kind}
-  EagerGestureRecognizer({ PointerDeviceKind kind }) : super(kind: kind);
+  EagerGestureRecognizer({ PointerDeviceKind? kind }) : super(kind: kind);
 
   @override
   void addAllowedPointer(PointerDownEvent event) {

packages/flutter/lib/src/gestures/force_press.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 Offset;
 
@@ -51,9 +50,9 @@ class ForcePressDetails {
   ///
   /// The [globalPosition] argument must not be null.
   ForcePressDetails({
-    @required this.globalPosition,
-    Offset localPosition,
-    @required this.pressure,
+    required this.globalPosition,
+    Offset? localPosition,
+    required this.pressure,
   }) : assert(globalPosition != null),
        assert(pressure != null),
        localPosition = localPosition ?? globalPosition;
@@ -128,8 +127,8 @@ class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
     this.startPressure = 0.4,
     this.peakPressure = 0.85,
     this.interpolation = _inverseLerp,
-    Object debugOwner,
-    PointerDeviceKind kind,
+    Object? debugOwner,
+    PointerDeviceKind? kind,
   }) : assert(startPressure != null),
        assert(peakPressure != null),
        assert(interpolation != null),
@@ -143,7 +142,7 @@ class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
   ///
   /// The position of the pointer is provided in the callback's `details`
   /// argument, which is a [ForcePressDetails] object.
-  GestureForcePressStartCallback onStart;
+  GestureForcePressStartCallback? onStart;
 
   /// A pointer is in contact with the screen and is either moving on the plane
   /// of the screen, pressing the screen with varying forces or both
@@ -154,7 +153,7 @@ class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
   /// matter what the pressure is during this time period. The position and
   /// pressure of the pointer is provided in the callback's `details` argument,
   /// which is a [ForcePressDetails] object.
-  GestureForcePressUpdateCallback onUpdate;
+  GestureForcePressUpdateCallback? onUpdate;
 
   /// A pointer is in contact with the screen and has just pressed with a force
   /// exceeding the [peakPressure]. This is an arbitrary second level action
@@ -163,13 +162,13 @@ class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
   ///
   /// The position of the pointer is provided in the callback's `details`
   /// argument, which is a [ForcePressDetails] object.
-  GestureForcePressPeakCallback onPeak;
+  GestureForcePressPeakCallback? onPeak;
 
   /// A pointer is no longer in contact with the screen.
   ///
   /// The position of the pointer is provided in the callback's `details`
   /// argument, which is a [ForcePressDetails] object.
-  GestureForcePressEndCallback onEnd;
+  GestureForcePressEndCallback? onEnd;
 
   /// The pressure of the press required to initiate a force press.
   ///
@@ -209,8 +208,8 @@ class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
   /// ```
   final GestureForceInterpolation interpolation;
 
-  OffsetPair _lastPosition;
-  double _lastPressure;
+  late OffsetPair _lastPosition;
+  late double _lastPressure;
   _ForceState _state = _ForceState.ready;
 
   @override
@@ -264,7 +263,7 @@ class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
       if (pressure > startPressure && _state == _ForceState.accepted) {
         _state = _ForceState.started;
         if (onStart != null) {
-          invokeCallback<void>('onStart', () => onStart(ForcePressDetails(
+          invokeCallback<void>('onStart', () => onStart!(ForcePressDetails(
             pressure: pressure,
             globalPosition: _lastPosition.global,
             localPosition: _lastPosition.local,
@@ -275,7 +274,7 @@ class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
          (_state == _ForceState.started)) {
         _state = _ForceState.peaked;
         if (onPeak != null) {
-          invokeCallback<void>('onPeak', () => onPeak(ForcePressDetails(
+          invokeCallback<void>('onPeak', () => onPeak!(ForcePressDetails(
             pressure: pressure,
             globalPosition: event.position,
             localPosition: event.localPosition,
@@ -285,7 +284,7 @@ class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
       if (onUpdate != null &&  !pressure.isNaN &&
          (_state == _ForceState.started || _state == _ForceState.peaked)) {
         if (onUpdate != null) {
-          invokeCallback<void>('onUpdate', () => onUpdate(ForcePressDetails(
+          invokeCallback<void>('onUpdate', () => onUpdate!(ForcePressDetails(
             pressure: pressure,
             globalPosition: event.position,
             localPosition: event.localPosition,
@@ -302,7 +301,7 @@ class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
       _state = _ForceState.accepted;
 
     if (onStart != null && _state == _ForceState.started) {
-      invokeCallback<void>('onStart', () => onStart(ForcePressDetails(
+      invokeCallback<void>('onStart', () => onStart!(ForcePressDetails(
         pressure: _lastPressure,
         globalPosition: _lastPosition.global,
         localPosition: _lastPosition.local,
@@ -319,7 +318,7 @@ class ForcePressGestureRecognizer extends OneSequenceGestureRecognizer {
     }
     if (wasAccepted && onEnd != null) {
       if (onEnd != null) {
-        invokeCallback<void>('onEnd', () => onEnd(ForcePressDetails(
+        invokeCallback<void>('onEnd', () => onEnd!(ForcePressDetails(
           pressure: 0.0,
           globalPosition: _lastPosition.global,
           localPosition: _lastPosition.local,

packages/flutter/lib/src/gestures/hit_test.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 'package:vector_math/vector_math_64.dart';
@@ -13,8 +12,7 @@ import 'events.dart';
 abstract class HitTestable {
   // This class is intended to be used as an interface, and should not be
   // extended directly; this constructor prevents instantiation and extension.
-  // ignore: unused_element
-  factory HitTestable._() => null;
+  HitTestable._();
 
   /// Check whether the given position hits this object.
   ///
@@ -27,8 +25,7 @@ abstract class HitTestable {
 abstract class HitTestDispatcher {
   // This class is intended to be used as an interface, and should not be
   // extended directly; this constructor prevents instantiation and extension.
-  // ignore: unused_element
-  factory HitTestDispatcher._() => null;
+  HitTestDispatcher._();
 
   /// Override this method to dispatch events.
   void dispatchEvent(PointerEvent event, HitTestResult result);
@@ -38,8 +35,7 @@ abstract class HitTestDispatcher {
 abstract class HitTestTarget {
   // This class is intended to be used as an interface, and should not be
   // extended directly; this constructor prevents instantiation and extension.
-  // ignore: unused_element
-  factory HitTestTarget._() => null;
+  HitTestTarget._();
 
   /// Override this method to receive events.
   void handleEvent(PointerEvent event, HitTestEntry entry);
@@ -67,8 +63,8 @@ class HitTestEntry {
   ///
   ///  * [BoxHitTestResult.addWithPaintTransform], which is used during hit testing
   ///    to build up this transform.
-  Matrix4 get transform => _transform;
-  Matrix4 _transform;
+  Matrix4? get transform => _transform;
+  Matrix4? _transform;
 }
 
 // A type of data that can be applied to a matrix by left-multiplication.

packages/flutter/lib/src/gestures/lsq_solver.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;
 import 'dart:typed_data';
@@ -76,7 +75,7 @@ class PolynomialFit {
   /// An indicator of the quality of the fit.
   ///
   /// Larger values indicate greater quality.
-  double confidence;
+  late double confidence;
 }
 
 /// Uses the least-squares algorithm to fit a polynomial to a set of data.
@@ -98,7 +97,9 @@ class LeastSquaresSolver {
   final List<double> w;
 
   /// Fits a polynomial of the given degree to the data points.
-  PolynomialFit solve(int degree) {
+  ///
+  /// When there is not enough data to fit a curve null is returned.
+  PolynomialFit? solve(int degree) {
     if (degree > x.length) // Not enough data to fit a curve.
       return null;
 

packages/flutter/lib/src/gestures/pointer_router.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 'package:vector_math/vector_math_64.dart';
@@ -14,8 +13,8 @@ typedef PointerRoute = void Function(PointerEvent event);
 
 /// A routing table for [PointerEvent] events.
 class PointerRouter {
-  final Map<int, Map<PointerRoute, Matrix4>> _routeMap = <int, Map<PointerRoute, Matrix4>>{};
-  final Map<PointerRoute, Matrix4> _globalRoutes = <PointerRoute, Matrix4>{};
+  final Map<int, Map<PointerRoute, Matrix4?>> _routeMap = <int, Map<PointerRoute, Matrix4?>>{};
+  final Map<PointerRoute, Matrix4?> _globalRoutes = <PointerRoute, Matrix4?>{};
 
   /// Adds a route to the routing table.
   ///
@@ -24,10 +23,10 @@ class PointerRouter {
   ///
   /// Routes added reentrantly within [PointerRouter.route] will take effect when
   /// routing the next event.
-  void addRoute(int pointer, PointerRoute route, [Matrix4 transform]) {
-    final Map<PointerRoute, Matrix4> routes = _routeMap.putIfAbsent(
+  void addRoute(int pointer, PointerRoute route, [Matrix4? transform]) {
+    final Map<PointerRoute, Matrix4?> routes = _routeMap.putIfAbsent(
       pointer,
-      () => <PointerRoute, Matrix4>{},
+      () => <PointerRoute, Matrix4?>{},
     );
     assert(!routes.containsKey(route));
     routes[route] = transform;
@@ -42,7 +41,7 @@ class PointerRouter {
   /// immediately.
   void removeRoute(int pointer, PointerRoute route) {
     assert(_routeMap.containsKey(pointer));
-    final Map<PointerRoute, Matrix4> routes = _routeMap[pointer];
+    final Map<PointerRoute, Matrix4?> routes = _routeMap[pointer]!;
     assert(routes.containsKey(route));
     routes.remove(route);
     if (routes.isEmpty)
@@ -55,7 +54,7 @@ class PointerRouter {
   ///
   /// Routes added reentrantly within [PointerRouter.route] will take effect when
   /// routing the next event.
-  void addGlobalRoute(PointerRoute route, [Matrix4 transform]) {
+  void addGlobalRoute(PointerRoute route, [Matrix4? transform]) {
     assert(!_globalRoutes.containsKey(route));
     _globalRoutes[route] = transform;
   }
@@ -72,12 +71,12 @@ class PointerRouter {
     _globalRoutes.remove(route);
   }
 
-  void _dispatch(PointerEvent event, PointerRoute route, Matrix4 transform) {
+  void _dispatch(PointerEvent event, PointerRoute route, Matrix4? transform) {
     try {
       event = event.transformed(transform);
       route(event);
     } catch (exception, stack) {
-      InformationCollector collector;
+      InformationCollector? collector;
       assert(() {
         collector = () sync* {
           yield DiagnosticsProperty<PointerRouter>('router', this, level: DiagnosticLevel.debug);
@@ -101,13 +100,13 @@ class PointerRouter {
   /// Routes are called in the order in which they were added to the
   /// PointerRouter object.
   void route(PointerEvent event) {
-    final Map<PointerRoute, Matrix4> routes = _routeMap[event.pointer];
-    final Map<PointerRoute, Matrix4> copiedGlobalRoutes = Map<PointerRoute, Matrix4>.from(_globalRoutes);
+    final Map<PointerRoute, Matrix4?>? routes = _routeMap[event.pointer];
+    final Map<PointerRoute, Matrix4?> copiedGlobalRoutes = Map<PointerRoute, Matrix4?>.from(_globalRoutes);
     if (routes != null) {
       _dispatchEventToRoutes(
         event,
         routes,
-        Map<PointerRoute, Matrix4>.from(routes),
+        Map<PointerRoute, Matrix4?>.from(routes),
       );
     }
     _dispatchEventToRoutes(event, _globalRoutes, copiedGlobalRoutes);
@@ -115,10 +114,10 @@ class PointerRouter {
 
   void _dispatchEventToRoutes(
     PointerEvent event,
-    Map<PointerRoute, Matrix4> referenceRoutes,
-    Map<PointerRoute, Matrix4> copiedRoutes,
+    Map<PointerRoute, Matrix4?> referenceRoutes,
+    Map<PointerRoute, Matrix4?> copiedRoutes,
   ) {
-    copiedRoutes.forEach((PointerRoute route, Matrix4 transform) {
+    copiedRoutes.forEach((PointerRoute route, Matrix4? transform) {
       if (referenceRoutes.containsKey(route)) {
         _dispatch(event, route, transform);
       }

packages/flutter/lib/src/gestures/pointer_signal_resolver.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';
 
@@ -27,15 +26,15 @@ bool _isSameEvent(PointerSignalEvent event1, PointerSignalEvent event2) {
 /// at the end of event dispatch. The first callback registered will be the one
 /// that is called.
 class PointerSignalResolver {
-  PointerSignalResolvedCallback _firstRegisteredCallback;
+  PointerSignalResolvedCallback? _firstRegisteredCallback;
 
-  PointerSignalEvent _currentEvent;
+  PointerSignalEvent? _currentEvent;
 
   /// Registers interest in handling [event].
   void register(PointerSignalEvent event, PointerSignalResolvedCallback callback) {
     assert(event != null);
     assert(callback != null);
-    assert(_currentEvent == null || _isSameEvent(_currentEvent, event));
+    assert(_currentEvent == null || _isSameEvent(_currentEvent!, event));
     if (_firstRegisteredCallback != null) {
       return;
     }
@@ -53,11 +52,11 @@ class PointerSignalResolver {
       assert(_currentEvent == null);
       return;
     }
-    assert(_isSameEvent(_currentEvent, event));
+    assert(_isSameEvent(_currentEvent!, event));
     try {
-      _firstRegisteredCallback(_currentEvent);
+      _firstRegisteredCallback!(_currentEvent!);
     } catch (exception, stack) {
-      InformationCollector collector;
+      InformationCollector? collector;
       assert(() {
         collector = () sync* {
           yield DiagnosticsProperty<PointerSignalEvent>('Event', event, style: DiagnosticsTreeStyle.errorProperty);

packages/flutter/lib/src/gestures/scale.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;
 
@@ -38,7 +37,7 @@ class ScaleStartDetails {
   /// Creates details for [GestureScaleStartCallback].
   ///
   /// The [focalPoint] argument must not be null.
-  ScaleStartDetails({ this.focalPoint = Offset.zero, Offset localFocalPoint, })
+  ScaleStartDetails({ this.focalPoint = Offset.zero, Offset? localFocalPoint, })
     : assert(focalPoint != null), localFocalPoint = localFocalPoint ?? focalPoint;
 
   /// The initial focal point of the pointers in contact with the screen.
@@ -75,7 +74,7 @@ class ScaleUpdateDetails {
   /// argument must be greater than or equal to zero.
   ScaleUpdateDetails({
     this.focalPoint = Offset.zero,
-    Offset localFocalPoint,
+    Offset? localFocalPoint,
     this.scale = 1.0,
     this.horizontalScale = 1.0,
     this.verticalScale = 1.0,
@@ -225,37 +224,37 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
   ///
   /// {@macro flutter.gestures.gestureRecognizer.kind}
   ScaleGestureRecognizer({
-    Object debugOwner,
-    PointerDeviceKind kind,
+    Object? debugOwner,
+    PointerDeviceKind? kind,
   }) : super(debugOwner: debugOwner, kind: kind);
 
   /// The pointers in contact with the screen have established a focal point and
   /// initial scale of 1.0.
-  GestureScaleStartCallback onStart;
+  GestureScaleStartCallback? onStart;
 
   /// The pointers in contact with the screen have indicated a new focal point
   /// and/or scale.
-  GestureScaleUpdateCallback onUpdate;
+  GestureScaleUpdateCallback? onUpdate;
 
   /// The pointers are no longer in contact with the screen.
-  GestureScaleEndCallback onEnd;
+  GestureScaleEndCallback? onEnd;
 
   _ScaleState _state = _ScaleState.ready;
 
-  Matrix4 _lastTransform;
-
-  Offset _initialFocalPoint;
-  Offset _currentFocalPoint;
-  double _initialSpan;
-  double _currentSpan;
-  double _initialHorizontalSpan;
-  double _currentHorizontalSpan;
-  double _initialVerticalSpan;
-  double _currentVerticalSpan;
-  _LineBetweenPointers _initialLine;
-  _LineBetweenPointers _currentLine;
-  Map<int, Offset> _pointerLocations;
-  List<int> _pointerQueue; // A queue to sort pointers in order of entrance
+  Matrix4? _lastTransform;
+
+  late Offset _initialFocalPoint;
+  late Offset _currentFocalPoint;
+  late double _initialSpan;
+  late double _currentSpan;
+  late double _initialHorizontalSpan;
+  late double _currentHorizontalSpan;
+  late double _initialVerticalSpan;
+  late double _currentVerticalSpan;
+  _LineBetweenPointers? _initialLine;
+  _LineBetweenPointers? _currentLine;
+  late Map<int, Offset> _pointerLocations;
+  late List<int> _pointerQueue; // A queue to sort pointers in order of entrance
   final Map<int, VelocityTracker> _velocityTrackers = <int, VelocityTracker>{};
 
   double get _scaleFactor => _initialSpan > 0.0 ? _currentSpan / _initialSpan : 1.0;
@@ -268,15 +267,15 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
     if (_initialLine == null || _currentLine == null) {
       return 0.0;
     }
-    final double fx = _initialLine.pointerStartLocation.dx;
-    final double fy = _initialLine.pointerStartLocation.dy;
-    final double sx = _initialLine.pointerEndLocation.dx;
-    final double sy = _initialLine.pointerEndLocation.dy;
+    final double fx = _initialLine!.pointerStartLocation.dx;
+    final double fy = _initialLine!.pointerStartLocation.dy;
+    final double sx = _initialLine!.pointerEndLocation.dx;
+    final double sy = _initialLine!.pointerEndLocation.dy;
 
-    final double nfx = _currentLine.pointerStartLocation.dx;
-    final double nfy = _currentLine.pointerStartLocation.dy;
-    final double nsx = _currentLine.pointerEndLocation.dx;
-    final double nsy = _currentLine.pointerEndLocation.dy;
+    final double nfx = _currentLine!.pointerStartLocation.dx;
+    final double nfy = _currentLine!.pointerStartLocation.dy;
+    final double nsx = _currentLine!.pointerEndLocation.dx;
+    final double nsy = _currentLine!.pointerEndLocation.dy;
 
     final double angle1 = math.atan2(fy - sy, fx - sx);
     final double angle2 = math.atan2(nfy - nsy, nfx - nsx);
@@ -307,8 +306,7 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
     bool didChangeConfiguration = false;
     bool shouldStartIfAccepted = false;
     if (event is PointerMoveEvent) {
-      final VelocityTracker tracker = _velocityTrackers[event.pointer];
-      assert(tracker != null);
+      final VelocityTracker tracker = _velocityTrackers[event.pointer]!;
       if (!event.synthesized)
         tracker.addPosition(event.timeStamp, event.position);
       _pointerLocations[event.pointer] = event.position;
@@ -341,7 +339,7 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
     // Compute the focal point
     Offset focalPoint = Offset.zero;
     for (final int pointer in _pointerLocations.keys)
-      focalPoint += _pointerLocations[pointer];
+      focalPoint += _pointerLocations[pointer]!;
     _currentFocalPoint = count > 0 ? focalPoint / count.toDouble() : Offset.zero;
 
     // Span is the average deviation from focal point. Horizontal and vertical
@@ -351,9 +349,9 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
     double totalHorizontalDeviation = 0.0;
     double totalVerticalDeviation = 0.0;
     for (final int pointer in _pointerLocations.keys) {
-      totalDeviation += (_currentFocalPoint - _pointerLocations[pointer]).distance;
-      totalHorizontalDeviation += (_currentFocalPoint.dx - _pointerLocations[pointer].dx).abs();
-      totalVerticalDeviation += (_currentFocalPoint.dy - _pointerLocations[pointer].dy).abs();
+      totalDeviation += (_currentFocalPoint - _pointerLocations[pointer]!).distance;
+      totalHorizontalDeviation += (_currentFocalPoint.dx - _pointerLocations[pointer]!.dx).abs();
+      totalVerticalDeviation += (_currentFocalPoint.dy - _pointerLocations[pointer]!.dy).abs();
     }
     _currentSpan = count > 0 ? totalDeviation / count : 0.0;
     _currentHorizontalSpan = count > 0 ? totalHorizontalDeviation / count : 0.0;
@@ -369,22 +367,22 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
     if (count < 2) {
       _initialLine = _currentLine;
     } else if (_initialLine != null &&
-      _initialLine.pointerStartId == _pointerQueue[0] &&
-      _initialLine.pointerEndId == _pointerQueue[1]) {
+      _initialLine!.pointerStartId == _pointerQueue[0] &&
+      _initialLine!.pointerEndId == _pointerQueue[1]) {
       /// Rotation updated, set the [_currentLine]
       _currentLine = _LineBetweenPointers(
         pointerStartId: _pointerQueue[0],
-        pointerStartLocation: _pointerLocations[_pointerQueue[0]],
+        pointerStartLocation: _pointerLocations[_pointerQueue[0]]!,
         pointerEndId: _pointerQueue[1],
-        pointerEndLocation: _pointerLocations[_pointerQueue[1]],
+        pointerEndLocation: _pointerLocations[_pointerQueue[1]]!,
       );
     } else {
       /// A new rotation process is on the way, set the [_initialLine]
       _initialLine = _LineBetweenPointers(
         pointerStartId: _pointerQueue[0],
-        pointerStartLocation: _pointerLocations[_pointerQueue[0]],
+        pointerStartLocation: _pointerLocations[_pointerQueue[0]]!,
         pointerEndId: _pointerQueue[1],
-        pointerEndLocation: _pointerLocations[_pointerQueue[1]],
+        pointerEndLocation: _pointerLocations[_pointerQueue[1]]!,
       );
       _currentLine = null;
     }
@@ -398,17 +396,16 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
     _initialVerticalSpan = _currentVerticalSpan;
     if (_state == _ScaleState.started) {
       if (onEnd != null) {
-        final VelocityTracker tracker = _velocityTrackers[pointer];
-        assert(tracker != null);
+        final VelocityTracker tracker = _velocityTrackers[pointer]!;
 
         Velocity velocity = tracker.getVelocity();
         if (_isFlingGesture(velocity)) {
           final Offset pixelsPerSecond = velocity.pixelsPerSecond;
           if (pixelsPerSecond.distanceSquared > kMaxFlingVelocity * kMaxFlingVelocity)
             velocity = Velocity(pixelsPerSecond: (pixelsPerSecond / pixelsPerSecond.distance) * kMaxFlingVelocity);
-          invokeCallback<void>('onEnd', () => onEnd(ScaleEndDetails(velocity: velocity)));
+          invokeCallback<void>('onEnd', () => onEnd!(ScaleEndDetails(velocity: velocity)));
         } else {
-          invokeCallback<void>('onEnd', () => onEnd(ScaleEndDetails(velocity: Velocity.zero)));
+          invokeCallback<void>('onEnd', () => onEnd!(ScaleEndDetails(velocity: Velocity.zero)));
         }
       }
       _state = _ScaleState.accepted;
@@ -437,7 +434,7 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
 
     if (_state == _ScaleState.started && onUpdate != null)
       invokeCallback<void>('onUpdate', () {
-        onUpdate(ScaleUpdateDetails(
+        onUpdate!(ScaleUpdateDetails(
           scale: _scaleFactor,
           horizontalScale: _horizontalScaleFactor,
           verticalScale: _verticalScaleFactor,
@@ -452,7 +449,7 @@ class ScaleGestureRecognizer extends OneSequenceGestureRecognizer {
     assert(_state == _ScaleState.started);
     if (onStart != null)
       invokeCallback<void>('onStart', () {
-        onStart(ScaleStartDetails(
+        onStart!(ScaleStartDetails(
           focalPoint: _currentFocalPoint,
           localFocalPoint: PointerEvent.transformPosition(_lastTransform, _currentFocalPoint),
         ));

packages/flutter/lib/src/gestures/team.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 'arena.dart';
 import 'binding.dart';
@@ -27,8 +26,8 @@ class _CombiningGestureArenaMember extends GestureArenaMember {
   final int _pointer;
 
   bool _resolved = false;
-  GestureArenaMember _winner;
-  GestureArenaEntry _entry;
+  GestureArenaMember? _winner;
+  GestureArenaEntry? _entry;
 
   @override
   void acceptGesture(int pointer) {
@@ -40,7 +39,7 @@ class _CombiningGestureArenaMember extends GestureArenaMember {
       if (member != _winner)
         member.rejectGesture(pointer);
     }
-    _winner.acceptGesture(pointer);
+    _winner!.acceptGesture(pointer);
   }
 
   @override
@@ -54,7 +53,7 @@ class _CombiningGestureArenaMember extends GestureArenaMember {
   void _close() {
     assert(!_resolved);
     _resolved = true;
-    final _CombiningGestureArenaMember combiner = _owner._combiners.remove(_pointer);
+    final _CombiningGestureArenaMember? combiner = _owner._combiners.remove(_pointer);
     assert(combiner == this);
   }
 
@@ -62,7 +61,7 @@ class _CombiningGestureArenaMember extends GestureArenaMember {
     assert(!_resolved);
     assert(_pointer == pointer);
     _members.add(member);
-    _entry ??= GestureBinding.instance.gestureArena.add(pointer, this);
+    _entry ??= GestureBinding.instance!.gestureArena.add(pointer, this);
     return _CombiningGestureArenaEntry(this, member);
   }
 
@@ -73,11 +72,11 @@ class _CombiningGestureArenaMember extends GestureArenaMember {
       _members.remove(member);
       member.rejectGesture(_pointer);
       if (_members.isEmpty)
-        _entry.resolve(disposition);
+        _entry!.resolve(disposition);
     } else {
       assert(disposition == GestureDisposition.accepted);
       _winner ??= _owner.captain ?? member;
-      _entry.resolve(disposition);
+      _entry!.resolve(disposition);
     }
   }
 }
@@ -131,7 +130,7 @@ class GestureArenaTeam {
   /// If not null, when any one of the [GestureArenaTeam] members claims victory
   /// the captain accepts the gesture.
   /// If null, the member that claims a victory accepts the gesture.
-  GestureArenaMember captain;
+  GestureArenaMember? captain;
 
   /// Adds a new member to the arena on behalf of this team.
   ///

packages/flutter/lib/src/gestures/velocity_tracker.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 Offset;
 
@@ -19,7 +18,7 @@ class Velocity {
   ///
   /// The [pixelsPerSecond] argument must not be null.
   const Velocity({
-    @required this.pixelsPerSecond,
+    required this.pixelsPerSecond,
   }) : assert(pixelsPerSecond != null);
 
   /// A velocity that isn't moving at all.
@@ -95,10 +94,10 @@ class VelocityEstimate {
   ///
   /// [pixelsPerSecond], [confidence], [duration], and [offset] must not be null.
   const VelocityEstimate({
-    @required this.pixelsPerSecond,
-    @required this.confidence,
-    @required this.duration,
-    @required this.offset,
+    required this.pixelsPerSecond,
+    required this.confidence,
+    required this.duration,
+    required this.offset,
   }) : assert(pixelsPerSecond != null),
        assert(confidence != null),
        assert(duration != null),
@@ -154,7 +153,7 @@ class VelocityTracker {
   static const int _minSampleSize = 3;
 
   // Circular buffer; current sample at _index.
-  final List<_PointAtTime> _samples = List<_PointAtTime>(_historySize);
+  final List<_PointAtTime?> _samples = List<_PointAtTime?>.filled(_historySize, null, growable: false);
   int _index = 0;
 
   /// Adds a position as the given time to the tracker.
@@ -171,7 +170,7 @@ class VelocityTracker {
   /// Information is added using [addPosition].
   ///
   /// Returns null if there is no data on which to base an estimate.
-  VelocityEstimate getVelocityEstimate() {
+  VelocityEstimate? getVelocityEstimate() {
     final List<double> x = <double>[];
     final List<double> y = <double>[];
     final List<double> w = <double>[];
@@ -179,7 +178,7 @@ class VelocityTracker {
     int sampleCount = 0;
     int index = _index;
 
-    final _PointAtTime newestSample = _samples[index];
+    final _PointAtTime? newestSample = _samples[index];
     if (newestSample == null)
       return null;
 
@@ -189,7 +188,7 @@ class VelocityTracker {
     // Starting with the most recent PointAtTime sample, iterate backwards while
     // the samples represent continuous motion.
     do {
-      final _PointAtTime sample = _samples[index];
+      final _PointAtTime? sample = _samples[index];
       if (sample == null)
         break;
 
@@ -212,10 +211,10 @@ class VelocityTracker {
 
     if (sampleCount >= _minSampleSize) {
       final LeastSquaresSolver xSolver = LeastSquaresSolver(time, x, w);
-      final PolynomialFit xFit = xSolver.solve(2);
+      final PolynomialFit? xFit = xSolver.solve(2);
       if (xFit != null) {
         final LeastSquaresSolver ySolver = LeastSquaresSolver(time, y, w);
-        final PolynomialFit yFit = ySolver.solve(2);
+        final PolynomialFit? yFit = ySolver.solve(2);
         if (yFit != null) {
           return VelocityEstimate( // convert from pixels/ms to pixels/s
             pixelsPerSecond: Offset(xFit.coefficients[1] * 1000, yFit.coefficients[1] * 1000),
@@ -245,7 +244,7 @@ class VelocityTracker {
   /// Returns [Velocity.zero] if there is no data from which to compute an
   /// estimate or if the estimated velocity is zero.
   Velocity getVelocity() {
-    final VelocityEstimate estimate = getVelocityEstimate();
+    final VelocityEstimate? estimate = getVelocityEstimate();
     if (estimate == null || estimate.pixelsPerSecond == Offset.zero)
       return Velocity.zero;
     return Velocity(pixelsPerSecond: estimate.pixelsPerSecond);