migration of material files to nullsafety (#66633)

packages/flutter/lib/src/material/arc.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:math' as math;
 import 'dart:ui' show lerpDouble;
 
@@ -38,15 +36,18 @@ class MaterialPointArcTween extends Tween<Offset> {
   /// first used, but the arguments can be null if the values are going to be
   /// filled in later.
   MaterialPointArcTween({
-    Offset begin,
-    Offset end,
+    Offset? begin,
+    Offset? end,
   }) : super(begin: begin, end: end);
 
   bool _dirty = true;
 
   void _initialize() {
-    assert(begin != null);
-    assert(end != null);
+    assert(this.begin != null);
+    assert(this.end != null);
+
+    final Offset begin = this.begin!;
+    final Offset end = this.end!;
 
     // An explanation with a diagram can be found at https://goo.gl/vMSdRg
     final Offset delta = end - begin;
@@ -55,12 +56,12 @@ class MaterialPointArcTween extends Tween<Offset> {
     final double distanceFromAtoB = delta.distance;
     final Offset c = Offset(end.dx, begin.dy);
 
-    double sweepAngle() => 2.0 * math.asin(distanceFromAtoB / (2.0 * _radius));
+    double sweepAngle() => 2.0 * math.asin(distanceFromAtoB / (2.0 * _radius!));
 
     if (deltaX > _kOnAxisDelta && deltaY > _kOnAxisDelta) {
       if (deltaX < deltaY) {
         _radius = distanceFromAtoB * distanceFromAtoB / (c - begin).distance / 2.0;
-        _center = Offset(end.dx + _radius * (begin.dx - end.dx).sign, end.dy);
+        _center = Offset(end.dx + _radius! * (begin.dx - end.dx).sign, end.dy);
         if (begin.dx < end.dx) {
           _beginAngle = sweepAngle() * (begin.dy - end.dy).sign;
           _endAngle = 0.0;
@@ -70,13 +71,13 @@ class MaterialPointArcTween extends Tween<Offset> {
         }
       } else {
         _radius = distanceFromAtoB * distanceFromAtoB / (c - end).distance / 2.0;
-        _center = Offset(begin.dx, begin.dy + (end.dy - begin.dy).sign * _radius);
+        _center = Offset(begin.dx, begin.dy + (end.dy - begin.dy).sign * _radius!);
         if (begin.dy < end.dy) {
           _beginAngle = -math.pi / 2.0;
-          _endAngle = _beginAngle + sweepAngle() * (end.dx - begin.dx).sign;
+          _endAngle = _beginAngle! + sweepAngle() * (end.dx - begin.dx).sign;
         } else {
           _beginAngle = math.pi / 2.0;
-          _endAngle = _beginAngle + sweepAngle() * (begin.dx - end.dx).sign;
+          _endAngle = _beginAngle! + sweepAngle() * (begin.dx - end.dx).sign;
         }
       }
       assert(_beginAngle != null);
@@ -90,56 +91,56 @@ class MaterialPointArcTween extends Tween<Offset> {
 
   /// The center of the circular arc, null if [begin] and [end] are horizontally or
   /// vertically aligned, or if either is null.
-  Offset get center {
+  Offset? get center {
     if (begin == null || end == null)
       return null;
     if (_dirty)
       _initialize();
     return _center;
   }
-  Offset _center;
+  Offset? _center;
 
   /// The radius of the circular arc, null if [begin] and [end] are horizontally or
   /// vertically aligned, or if either is null.
-  double get radius {
+  double? get radius {
     if (begin == null || end == null)
       return null;
     if (_dirty)
       _initialize();
     return _radius;
   }
-  double _radius;
+  double? _radius;
 
   /// The beginning of the arc's sweep in radians, measured from the positive x
   /// axis. Positive angles turn clockwise.
   ///
   /// This will be null if [begin] and [end] are horizontally or vertically
   /// aligned, or if either is null.
-  double get beginAngle {
+  double? get beginAngle {
     if (begin == null || end == null)
       return null;
     if (_dirty)
       _initialize();
     return _beginAngle;
   }
-  double _beginAngle;
+  double? _beginAngle;
 
   /// The end of the arc's sweep in radians, measured from the positive x axis.
   /// Positive angles turn clockwise.
   ///
   /// This will be null if [begin] and [end] are horizontally or vertically
   /// aligned, or if either is null.
-  double get endAngle {
+  double? get endAngle {
     if (begin == null || end == null)
       return null;
     if (_dirty)
       _initialize();
     return _beginAngle;
   }
-  double _endAngle;
+  double? _endAngle;
 
   @override
-  set begin(Offset value) {
+  set begin(Offset? value) {
     if (value != begin) {
       super.begin = value;
       _dirty = true;
@@ -147,7 +148,7 @@ class MaterialPointArcTween extends Tween<Offset> {
   }
 
   @override
-  set end(Offset value) {
+  set end(Offset? value) {
     if (value != end) {
       super.end = value;
       _dirty = true;
@@ -159,15 +160,15 @@ class MaterialPointArcTween extends Tween<Offset> {
     if (_dirty)
       _initialize();
     if (t == 0.0)
-      return begin;
+      return begin!;
     if (t == 1.0)
-      return end;
+      return end!;
     if (_beginAngle == null || _endAngle == null)
-      return Offset.lerp(begin, end, t);
-    final double angle = lerpDouble(_beginAngle, _endAngle, t);
-    final double x = math.cos(angle) * _radius;
-    final double y = math.sin(angle) * _radius;
-    return _center + Offset(x, y);
+      return Offset.lerp(begin, end, t)!;
+    final double angle = lerpDouble(_beginAngle, _endAngle, t)!;
+    final double x = math.cos(angle) * _radius!;
+    final double y = math.sin(angle) * _radius!;
+    return _center! + Offset(x, y);
   }
 
   @override
@@ -200,8 +201,8 @@ typedef _KeyFunc<T> = double Function(T input);
 
 // Select the element for which the key function returns the maximum value.
 T _maxBy<T>(Iterable<T> input, _KeyFunc<T> keyFunc) {
-  T maxValue;
-  double maxKey;
+  late T maxValue;
+  double? maxKey;
   for (final T value in input) {
     final double key = keyFunc(value);
     if (maxKey == null || key > maxKey) {
@@ -238,8 +239,8 @@ class MaterialRectArcTween extends RectTween {
   /// first used, but the arguments can be null if the values are going to be
   /// filled in later.
   MaterialRectArcTween({
-    Rect begin,
-    Rect end,
+    Rect? begin,
+    Rect? end,
   }) : super(begin: begin, end: end);
 
   bool _dirty = true;
@@ -247,21 +248,21 @@ class MaterialRectArcTween extends RectTween {
   void _initialize() {
     assert(begin != null);
     assert(end != null);
-    final Offset centersVector = end.center - begin.center;
+    final Offset centersVector = end!.center - begin!.center;
     final _Diagonal diagonal = _maxBy<_Diagonal>(_allDiagonals, (_Diagonal d) => _diagonalSupport(centersVector, d));
     _beginArc = MaterialPointArcTween(
-      begin: _cornerFor(begin, diagonal.beginId),
-      end: _cornerFor(end, diagonal.beginId),
+      begin: _cornerFor(begin!, diagonal.beginId),
+      end: _cornerFor(end!, diagonal.beginId),
     );
     _endArc = MaterialPointArcTween(
-      begin: _cornerFor(begin, diagonal.endId),
-      end: _cornerFor(end, diagonal.endId),
+      begin: _cornerFor(begin!, diagonal.endId),
+      end: _cornerFor(end!, diagonal.endId),
     );
     _dirty = false;
   }
 
   double _diagonalSupport(Offset centersVector, _Diagonal diagonal) {
-    final Offset delta = _cornerFor(begin, diagonal.endId) - _cornerFor(begin, diagonal.beginId);
+    final Offset delta = _cornerFor(begin!, diagonal.endId) - _cornerFor(begin!, diagonal.beginId);
     final double length = delta.distance;
     return centersVector.dx * delta.dx / length + centersVector.dy * delta.dy / length;
   }
@@ -273,33 +274,32 @@ class MaterialRectArcTween extends RectTween {
       case _CornerId.bottomLeft: return rect.bottomLeft;
       case _CornerId.bottomRight: return rect.bottomRight;
     }
-    return Offset.zero;
   }
 
   /// The path of the corresponding [begin], [end] rectangle corners that lead
   /// the animation.
-  MaterialPointArcTween get beginArc {
+  MaterialPointArcTween? get beginArc {
     if (begin == null)
       return null;
     if (_dirty)
       _initialize();
     return _beginArc;
   }
-  MaterialPointArcTween _beginArc;
+  late MaterialPointArcTween _beginArc;
 
   /// The path of the corresponding [begin], [end] rectangle corners that trail
   /// the animation.
-  MaterialPointArcTween get endArc {
+  MaterialPointArcTween? get endArc {
     if (end == null)
       return null;
     if (_dirty)
       _initialize();
     return _endArc;
   }
-  MaterialPointArcTween _endArc;
+  late MaterialPointArcTween _endArc;
 
   @override
-  set begin(Rect value) {
+  set begin(Rect? value) {
     if (value != begin) {
       super.begin = value;
       _dirty = true;
@@ -307,7 +307,7 @@ class MaterialRectArcTween extends RectTween {
   }
 
   @override
-  set end(Rect value) {
+  set end(Rect? value) {
     if (value != end) {
       super.end = value;
       _dirty = true;
@@ -319,9 +319,9 @@ class MaterialRectArcTween extends RectTween {
     if (_dirty)
       _initialize();
     if (t == 0.0)
-      return begin;
+      return begin!;
     if (t == 1.0)
-      return end;
+      return end!;
     return Rect.fromPoints(_beginArc.lerp(t), _endArc.lerp(t));
   }
 
@@ -354,8 +354,8 @@ class MaterialRectCenterArcTween extends RectTween {
   /// first used, but the arguments can be null if the values are going to be
   /// filled in later.
   MaterialRectCenterArcTween({
-    Rect begin,
-    Rect end,
+    Rect? begin,
+    Rect? end,
   }) : super(begin: begin, end: end);
 
   bool _dirty = true;
@@ -364,25 +364,25 @@ class MaterialRectCenterArcTween extends RectTween {
     assert(begin != null);
     assert(end != null);
     _centerArc = MaterialPointArcTween(
-      begin: begin.center,
-      end: end.center,
+      begin: begin!.center,
+      end: end!.center,
     );
     _dirty = false;
   }
 
   /// If [begin] and [end] are non-null, returns a tween that interpolates along
   /// a circular arc between [begin]'s [Rect.center] and [end]'s [Rect.center].
-  MaterialPointArcTween get centerArc {
+  MaterialPointArcTween? get centerArc {
     if (begin == null || end == null)
       return null;
     if (_dirty)
       _initialize();
     return _centerArc;
   }
-  MaterialPointArcTween _centerArc;
+  late MaterialPointArcTween _centerArc;
 
   @override
-  set begin(Rect value) {
+  set begin(Rect? value) {
     if (value != begin) {
       super.begin = value;
       _dirty = true;
@@ -390,7 +390,7 @@ class MaterialRectCenterArcTween extends RectTween {
   }
 
   @override
-  set end(Rect value) {
+  set end(Rect? value) {
     if (value != end) {
       super.end = value;
       _dirty = true;
@@ -402,12 +402,12 @@ class MaterialRectCenterArcTween extends RectTween {
     if (_dirty)
       _initialize();
     if (t == 0.0)
-      return begin;
+      return begin!;
     if (t == 1.0)
-      return end;
+      return end!;
     final Offset center = _centerArc.lerp(t);
-    final double width = lerpDouble(begin.width, end.width, t);
-    final double height = lerpDouble(begin.height, end.height, t);
+    final double width = lerpDouble(begin!.width, end!.width, t)!;
+    final double height = lerpDouble(begin!.height, end!.height, t)!;
     return Rect.fromLTWH(center.dx - width / 2.0, center.dy - height / 2.0, width, height);
   }
 

packages/flutter/lib/src/material/bottom_sheet_theme.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:ui' show lerpDouble;
 
 import 'package:flutter/foundation.dart';
@@ -41,43 +39,43 @@ class BottomSheetThemeData with Diagnosticable {
   /// Default value for [BottomSheet.backgroundColor].
   ///
   /// If null, [BottomSheet] defaults to [Material]'s default.
-  final Color backgroundColor;
+  final Color? backgroundColor;
 
   /// Default value for [BottomSheet.elevation].
   ///
   /// {@macro flutter.material.material.elevation}
   ///
   /// If null, [BottomSheet] defaults to 0.0.
-  final double elevation;
+  final double? elevation;
 
   /// Value for [BottomSheet.backgroundColor] when the Bottom sheet is presented
   /// as a modal bottom sheet.
-  final Color modalBackgroundColor;
+  final Color? modalBackgroundColor;
 
   /// Value for [BottomSheet.elevation] when the Bottom sheet is presented as a
   /// modal bottom sheet.
-  final double modalElevation;
+  final double? modalElevation;
 
   /// Default value for [BottomSheet.shape].
   ///
   /// If null, no overriding shape is specified for [BottomSheet], so the
   /// [BottomSheet] is rectangular.
-  final ShapeBorder shape;
+  final ShapeBorder? shape;
 
   /// Default value for [BottomSheet.clipBehavior].
   ///
   /// If null, [BottomSheet] uses [Clip.none].
-  final Clip clipBehavior;
+  final Clip? clipBehavior;
 
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   BottomSheetThemeData copyWith({
-    Color backgroundColor,
-    double elevation,
-    Color modalBackgroundColor,
-    double modalElevation,
-    ShapeBorder shape,
-    Clip clipBehavior,
+    Color? backgroundColor,
+    double? elevation,
+    Color? modalBackgroundColor,
+    double? modalElevation,
+    ShapeBorder? shape,
+    Clip? clipBehavior,
   }) {
     return BottomSheetThemeData(
       backgroundColor: backgroundColor ?? this.backgroundColor,
@@ -94,7 +92,7 @@ class BottomSheetThemeData with Diagnosticable {
   /// If both arguments are null then null is returned.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static BottomSheetThemeData lerp(BottomSheetThemeData a, BottomSheetThemeData b, double t) {
+  static BottomSheetThemeData? lerp(BottomSheetThemeData? a, BottomSheetThemeData? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;

packages/flutter/lib/src/material/colors.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:ui' show Color;
 
 import 'package:flutter/painting.dart';
@@ -27,34 +25,34 @@ class MaterialColor extends ColorSwatch<int> {
   const MaterialColor(int primary, Map<int, Color> swatch) : super(primary, swatch);
 
   /// The lightest shade.
-  Color get shade50 => this[50];
+  Color get shade50 => this[50]!;
 
   /// The second lightest shade.
-  Color get shade100 => this[100];
+  Color get shade100 => this[100]!;
 
   /// The third lightest shade.
-  Color get shade200 => this[200];
+  Color get shade200 => this[200]!;
 
   /// The fourth lightest shade.
-  Color get shade300 => this[300];
+  Color get shade300 => this[300]!;
 
   /// The fifth lightest shade.
-  Color get shade400 => this[400];
+  Color get shade400 => this[400]!;
 
   /// The default shade.
-  Color get shade500 => this[500];
+  Color get shade500 => this[500]!;
 
   /// The fourth darkest shade.
-  Color get shade600 => this[600];
+  Color get shade600 => this[600]!;
 
   /// The third darkest shade.
-  Color get shade700 => this[700];
+  Color get shade700 => this[700]!;
 
   /// The second darkest shade.
-  Color get shade800 => this[800];
+  Color get shade800 => this[800]!;
 
   /// The darkest shade.
-  Color get shade900 => this[900];
+  Color get shade900 => this[900]!;
 }
 
 /// Defines a single accent color as well a swatch of four shades of the
@@ -75,19 +73,19 @@ class MaterialAccentColor extends ColorSwatch<int> {
   const MaterialAccentColor(int primary, Map<int, Color> swatch) : super(primary, swatch);
 
   /// The lightest shade.
-  Color get shade50 => this[50];
+  Color get shade50 => this[50]!;
 
   /// The second lightest shade.
-  Color get shade100 => this[100];
+  Color get shade100 => this[100]!;
 
   /// The default shade.
-  Color get shade200 => this[200];
+  Color get shade200 => this[200]!;
 
   /// The second darkest shade.
-  Color get shade400 => this[400];
+  Color get shade400 => this[400]!;
 
   /// The darkest shade.
-  Color get shade700 => this[700];
+  Color get shade700 => this[700]!;
 }
 
 /// [Color] and [ColorSwatch] constants which represent Material design's

packages/flutter/lib/src/material/constants.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 'package:flutter/painting.dart';
 
 /// The minimum dimension of any interactive region according to Material

packages/flutter/lib/src/material/curves.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 'package:flutter/animation.dart';
 
 // The easing curves of the Material Library

packages/flutter/lib/src/material/floating_action_button_theme.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:ui' show lerpDouble;
 
 import 'package:flutter/foundation.dart';
@@ -48,63 +46,63 @@ class FloatingActionButtonThemeData with Diagnosticable {
 
   /// Color to be used for the unselected, enabled [FloatingActionButton]'s
   /// foreground.
-  final Color foregroundColor;
+  final Color? foregroundColor;
 
   /// Color to be used for the unselected, enabled [FloatingActionButton]'s
   /// background.
-  final Color backgroundColor;
+  final Color? backgroundColor;
 
   /// The color to use for filling the button when the button has input focus.
-  final Color focusColor;
+  final Color? focusColor;
 
   /// The color to use for filling the button when the button has a pointer
   /// hovering over it.
-  final Color hoverColor;
+  final Color? hoverColor;
 
   /// The splash color for this [FloatingActionButton]'s [InkWell].
-  final Color splashColor;
+  final Color? splashColor;
 
   /// The z-coordinate to be used for the unselected, enabled
   /// [FloatingActionButton]'s elevation foreground.
-  final double elevation;
+  final double? elevation;
 
   /// The z-coordinate at which to place this button relative to its parent when
   /// the button has the input focus.
   ///
   /// This controls the size of the shadow below the floating action button.
-  final double focusElevation;
+  final double? focusElevation;
 
   /// The z-coordinate at which to place this button relative to its parent when
   /// the button is enabled and has a pointer hovering over it.
   ///
   /// This controls the size of the shadow below the floating action button.
-  final double hoverElevation;
+  final double? hoverElevation;
 
   /// The z-coordinate to be used for the disabled [FloatingActionButton]'s
   /// elevation foreground.
-  final double disabledElevation;
+  final double? disabledElevation;
 
   /// The z-coordinate to be used for the selected, enabled
   /// [FloatingActionButton]'s elevation foreground.
-  final double highlightElevation;
+  final double? highlightElevation;
 
   /// The shape to be used for the floating action button's [Material].
-  final ShapeBorder shape;
+  final ShapeBorder? shape;
 
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   FloatingActionButtonThemeData copyWith({
-    Color foregroundColor,
-    Color backgroundColor,
-    Color focusColor,
-    Color hoverColor,
-    Color splashColor,
-    double elevation,
-    double focusElevation,
-    double hoverElevation,
-    double disabledElevation,
-    double highlightElevation,
-    ShapeBorder shape,
+    Color? foregroundColor,
+    Color? backgroundColor,
+    Color? focusColor,
+    Color? hoverColor,
+    Color? splashColor,
+    double? elevation,
+    double? focusElevation,
+    double? hoverElevation,
+    double? disabledElevation,
+    double? highlightElevation,
+    ShapeBorder? shape,
   }) {
     return FloatingActionButtonThemeData(
       foregroundColor: foregroundColor ?? this.foregroundColor,
@@ -126,7 +124,7 @@ class FloatingActionButtonThemeData with Diagnosticable {
   /// If both arguments are null then null is returned.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static FloatingActionButtonThemeData lerp(FloatingActionButtonThemeData a, FloatingActionButtonThemeData b, double t) {
+  static FloatingActionButtonThemeData? lerp(FloatingActionButtonThemeData? a, FloatingActionButtonThemeData? b, double t) {
     assert(t != null);
     if (a == null && b == null)
       return null;

packages/flutter/lib/src/material/flutter_logo.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 'package:flutter/widgets.dart';
 
 /// The Flutter logo, in widget form. This widget respects the [IconTheme].
@@ -22,7 +20,7 @@ class FlutterLogo extends StatelessWidget {
   /// The [textColor], [style], [duration], and [curve] arguments must not be
   /// null.
   const FlutterLogo({
-    Key key,
+    Key? key,
     this.size,
     this.textColor = const Color(0xFF757575),
     this.style = FlutterLogoStyle.markOnly,
@@ -41,7 +39,7 @@ class FlutterLogo extends StatelessWidget {
   /// Defaults to the current [IconTheme] size, if any. If there is no
   /// [IconTheme], or it does not specify an explicit size, then it defaults to
   /// 24.0.
-  final double size;
+  final double? size;
 
   /// The color used to paint the "Flutter" text on the logo, if [style] is
   /// [FlutterLogoStyle.horizontal] or [FlutterLogoStyle.stacked].
@@ -64,7 +62,7 @@ class FlutterLogo extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final IconThemeData iconTheme = IconTheme.of(context);
-    final double iconSize = size ?? iconTheme.size;
+    final double? iconSize = size ?? iconTheme.size;
     return AnimatedContainer(
       width: iconSize,
       height: iconSize,

packages/flutter/lib/src/material/grid_tile.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 'package:flutter/widgets.dart';
 
 /// A tile in a material design grid list.
@@ -23,22 +21,22 @@ class GridTile extends StatelessWidget {
   ///
   /// Must have a child. Does not typically have both a header and a footer.
   const GridTile({
-    Key key,
+    Key? key,
     this.header,
     this.footer,
-    @required this.child,
+    required this.child,
   }) : assert(child != null),
        super(key: key);
 
   /// The widget to show over the top of this grid tile.
   ///
   /// Typically a [GridTileBar].
-  final Widget header;
+  final Widget? header;
 
   /// The widget to show over the bottom of this grid tile.
   ///
   /// Typically a [GridTileBar].
-  final Widget footer;
+  final Widget? footer;
 
   /// The widget that fills the tile.
   ///
@@ -60,14 +58,14 @@ class GridTile extends StatelessWidget {
             top: 0.0,
             left: 0.0,
             right: 0.0,
-            child: header,
+            child: header!,
           ),
         if (footer != null)
           Positioned(
             left: 0.0,
             bottom: 0.0,
             right: 0.0,
-            child: footer,
+            child: footer!,
           ),
       ],
     );

packages/flutter/lib/src/material/icons.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 'package:flutter/widgets.dart';
 
 /// Identifiers for the supported material design icons.

packages/flutter/lib/src/material/material_state.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:ui' show Color;
 
 import 'package:flutter/foundation.dart';
@@ -76,7 +74,7 @@ enum MaterialState {
 
 /// Signature for the function that returns a value of type `T` based on a given
 /// set of states.
-typedef MaterialPropertyResolver<T> = T Function(Set<MaterialState> states);
+typedef MaterialPropertyResolver<T> = T? Function(Set<MaterialState> states);
 
 /// Defines a [Color] that is also a [MaterialStateProperty].
 ///
@@ -139,7 +137,7 @@ abstract class MaterialStateColor extends Color implements MaterialStateProperty
   /// Returns a [Color] that's to be used when a Material component is in the
   /// specified state.
   @override
-  Color resolve(Set<MaterialState> states);
+  Color? resolve(Set<MaterialState> states);
 }
 
 /// A [MaterialStateColor] created from a [MaterialPropertyResolver<Color>]
@@ -150,7 +148,7 @@ abstract class MaterialStateColor extends Color implements MaterialStateProperty
 ///
 /// Used by [MaterialStateColor.resolveWith].
 class _MaterialStateColor extends MaterialStateColor {
-  _MaterialStateColor(this._resolve) : super(_resolve(_defaultStates).value);
+  _MaterialStateColor(this._resolve) : super(_resolve(_defaultStates)!.value);
 
   final MaterialPropertyResolver<Color> _resolve;
 
@@ -158,7 +156,7 @@ class _MaterialStateColor extends MaterialStateColor {
   static const Set<MaterialState> _defaultStates = <MaterialState>{};
 
   @override
-  Color resolve(Set<MaterialState> states) => _resolve(states);
+  Color? resolve(Set<MaterialState> states) => _resolve(states);
 }
 
 /// Defines a [MouseCursor] whose value depends on a set of [MaterialState]s which
@@ -224,7 +222,7 @@ abstract class MaterialStateMouseCursor extends MouseCursor implements MaterialS
   @protected
   @override
   MouseCursorSession createSession(int device) {
-    return resolve(<MaterialState>{}).createSession(device);
+    return resolve(<MaterialState>{})!.createSession(device);
   }
 
   /// Returns a [MouseCursor] that's to be used when a Material component is in
@@ -232,7 +230,7 @@ abstract class MaterialStateMouseCursor extends MouseCursor implements MaterialS
   ///
   /// This method should never return null.
   @override
-  MouseCursor resolve(Set<MaterialState> states);
+  MouseCursor? resolve(Set<MaterialState> states);
 
   /// A mouse cursor for clickable material widgets, which resolves differently
   /// when the widget is disabled.
@@ -263,9 +261,9 @@ abstract class MaterialStateMouseCursor extends MouseCursor implements MaterialS
 
 class _EnabledAndDisabledMouseCursor extends MaterialStateMouseCursor {
   const _EnabledAndDisabledMouseCursor({
-    this.enabledCursor,
-    this.disabledCursor,
-    this.name,
+    required this.enabledCursor,
+    required this.disabledCursor,
+    required this.name,
   });
 
   final MouseCursor enabledCursor;
@@ -349,7 +347,7 @@ abstract class MaterialStateProperty<T> {
   /// Widgets like [TextButton] and [ElevatedButton] apply this method to their
   /// current [MaterialState]s to compute colors and other visual parameters
   /// at build time.
-  T resolve(Set<MaterialState> states);
+  T? resolve(Set<MaterialState> states);
 
   /// Resolves the value for the given set of states if `value` is a
   /// [MaterialStateProperty], otherwise returns the value itself.
@@ -357,9 +355,9 @@ abstract class MaterialStateProperty<T> {
   /// This is useful for widgets that have parameters which can optionally be a
   /// [MaterialStateProperty]. For example, [InkWell.mouseCursor] can be a
   /// [MouseCursor] or a [MaterialStateProperty<MouseCursor>].
-  static T resolveAs<T>(T value, Set<MaterialState> states) {
+  static T? resolveAs<T>(T? value, Set<MaterialState> states) {
     if (value is MaterialStateProperty<T>) {
-      final MaterialStateProperty<T> property = value;
+      final MaterialStateProperty<T> property = value as MaterialStateProperty<T>;
       return property.resolve(states);
     }
     return value;
@@ -371,7 +369,7 @@ abstract class MaterialStateProperty<T> {
 
   /// Convenience method for creating a [MaterialStateProperty] that resolves
   /// to a single value for all states.
-  static MaterialStateProperty<T> all<T>(T value) => _MaterialStatePropertyAll<T>(value);
+  static MaterialStateProperty<T> all<T>(T? value) => _MaterialStatePropertyAll<T>(value);
 }
 
 class _MaterialStatePropertyWith<T> implements MaterialStateProperty<T> {
@@ -380,16 +378,16 @@ class _MaterialStatePropertyWith<T> implements MaterialStateProperty<T> {
   final MaterialPropertyResolver<T> _resolve;
 
   @override
-  T resolve(Set<MaterialState> states) => _resolve(states);
+  T? resolve(Set<MaterialState> states) => _resolve(states);
 }
 
 class _MaterialStatePropertyAll<T> implements MaterialStateProperty<T> {
   _MaterialStatePropertyAll(this.value);
 
-  final T value;
+  final T? value;
 
   @override
-  T resolve(Set<MaterialState> states) => value;
+  T? resolve(Set<MaterialState> states) => value;
 
   @override
   String toString() => 'MaterialStateProperty.all($value)';

packages/flutter/lib/src/material/text_theme.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 'package:flutter/foundation.dart';
 import 'package:flutter/painting.dart';
 
@@ -113,16 +111,16 @@ class TextTheme with Diagnosticable {
   /// If you do decide to create your own text theme, consider using one of
   /// those predefined themes as a starting point for [copyWith] or [apply].
   const TextTheme({
-    TextStyle headline1,
-    TextStyle headline2,
-    TextStyle headline3,
-    TextStyle headline4,
-    TextStyle headline5,
-    TextStyle headline6,
-    TextStyle subtitle1,
-    TextStyle subtitle2,
-    TextStyle bodyText1,
-    TextStyle bodyText2,
+    TextStyle? headline1,
+    TextStyle? headline2,
+    TextStyle? headline3,
+    TextStyle? headline4,
+    TextStyle? headline5,
+    TextStyle? headline6,
+    TextStyle? subtitle1,
+    TextStyle? subtitle2,
+    TextStyle? bodyText1,
+    TextStyle? bodyText2,
     this.caption,
     this.button,
     this.overline,
@@ -130,52 +128,52 @@ class TextTheme with Diagnosticable {
       'This is the term used in the 2014 version of material design. The modern term is headline1. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle display4,
+    TextStyle? display4,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline2. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle display3,
+    TextStyle? display3,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline3. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle display2,
+    TextStyle? display2,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline4. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle display1,
+    TextStyle? display1,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline5. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle headline,
+    TextStyle? headline,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline6. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle title,
+    TextStyle? title,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is subtitle1. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle subhead,
+    TextStyle? subhead,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is subtitle2. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle subtitle,
+    TextStyle? subtitle,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is bodyText1. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle body2,
+    TextStyle? body2,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is bodyText2. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle body1,
+    TextStyle? body1,
   }) : assert(
          (headline1 == null && headline2 == null && headline3 == null && headline4 == null && headline5 == null && headline6 == null &&
           subtitle1 == null && subtitle2 == null &&
@@ -195,49 +193,49 @@ class TextTheme with Diagnosticable {
        bodyText2 = bodyText2 ?? body1;
 
   /// Extremely large text.
-  final TextStyle headline1;
+  final TextStyle? headline1;
 
   /// Very, very large text.
   ///
   /// Used for the date in the dialog shown by [showDatePicker].
-  final TextStyle headline2;
+  final TextStyle? headline2;
 
   /// Very large text.
-  final TextStyle headline3;
+  final TextStyle? headline3;
 
   /// Large text.
-  final TextStyle headline4;
+  final TextStyle? headline4;
 
   /// Used for large text in dialogs (e.g., the month and year in the dialog
   /// shown by [showDatePicker]).
-  final TextStyle headline5;
+  final TextStyle? headline5;
 
   /// Used for the primary text in app bars and dialogs (e.g., [AppBar.title]
   /// and [AlertDialog.title]).
-  final TextStyle headline6;
+  final TextStyle? headline6;
 
   /// Used for the primary text in lists (e.g., [ListTile.title]).
-  final TextStyle subtitle1;
+  final TextStyle? subtitle1;
 
   /// For medium emphasis text that's a little smaller than [subtitle1].
-  final TextStyle subtitle2;
+  final TextStyle? subtitle2;
 
   /// Used for emphasizing text that would otherwise be [bodyText2].
-  final TextStyle bodyText1;
+  final TextStyle? bodyText1;
 
   /// The default text style for [Material].
-  final TextStyle bodyText2;
+  final TextStyle? bodyText2;
 
   /// Used for auxiliary text associated with images.
-  final TextStyle caption;
+  final TextStyle? caption;
 
   /// Used for text on [ElevatedButton], [TextButton] and [OutlinedButton].
-  final TextStyle button;
+  final TextStyle? button;
 
   /// The smallest style.
   ///
   /// Typically used for captions or to introduce a (larger) headline.
-  final TextStyle overline;
+  final TextStyle? overline;
 
   /// Extremely large text.
   ///
@@ -247,7 +245,7 @@ class TextTheme with Diagnosticable {
     'This is the term used in the 2014 version of material design. The modern term is headline1. '
     'This feature was deprecated after v1.13.8.'
   )
-  TextStyle get display4 => headline1;
+  TextStyle? get display4 => headline1;
 
   /// Very, very large text.
   ///
@@ -257,7 +255,7 @@ class TextTheme with Diagnosticable {
     'This is the term used in the 2014 version of material design. The modern term is headline2. '
     'This feature was deprecated after v1.13.8.'
   )
-  TextStyle get display3 => headline2;
+  TextStyle? get display3 => headline2;
 
   /// Very large text.
   ///
@@ -267,7 +265,7 @@ class TextTheme with Diagnosticable {
     'This is the term used in the 2014 version of material design. The modern term is headline3. '
     'This feature was deprecated after v1.13.8.'
   )
-  TextStyle get display2 => headline3;
+  TextStyle? get display2 => headline3;
 
   /// Large text.
   ///
@@ -277,7 +275,7 @@ class TextTheme with Diagnosticable {
     'This is the term used in the 2014 version of material design. The modern term is headline4. '
     'This feature was deprecated after v1.13.8.'
   )
-  TextStyle get display1 => headline4;
+  TextStyle? get display1 => headline4;
 
   /// Used for large text in dialogs.
   ///
@@ -287,7 +285,7 @@ class TextTheme with Diagnosticable {
     'This is the term used in the 2014 version of material design. The modern term is headline5. '
     'This feature was deprecated after v1.13.8.'
   )
-  TextStyle get headline => headline5;
+  TextStyle? get headline => headline5;
 
   /// Used for the primary text in app bars and dialogs.
   ///
@@ -297,7 +295,7 @@ class TextTheme with Diagnosticable {
     'This is the term used in the 2014 version of material design. The modern term is headline6. '
     'This feature was deprecated after v1.13.8.'
   )
-  TextStyle get title => headline6;
+  TextStyle? get title => headline6;
 
   /// Used for the primary text in lists (e.g., [ListTile.title]).
   ///
@@ -307,7 +305,7 @@ class TextTheme with Diagnosticable {
     'This is the term used in the 2014 version of material design. The modern term is subtitle1. '
     'This feature was deprecated after v1.13.8.'
   )
-  TextStyle get subhead => subtitle1;
+  TextStyle? get subhead => subtitle1;
 
   /// For medium emphasis text that's a little smaller than [subhead].
   ///
@@ -317,7 +315,7 @@ class TextTheme with Diagnosticable {
     'This is the term used in the 2014 version of material design. The modern term is subtitle2. '
     'This feature was deprecated after v1.13.8.'
   )
-  TextStyle get subtitle => subtitle2;
+  TextStyle? get subtitle => subtitle2;
 
   /// Used for emphasizing text that would otherwise be [body1].
   ///
@@ -328,7 +326,7 @@ class TextTheme with Diagnosticable {
     'This is the term used in the 2014 version of material design. The modern term is bodyText1. '
     'This feature was deprecated after v1.13.8.'
   )
-  TextStyle get body2 => bodyText1;
+  TextStyle? get body2 => bodyText1;
 
   /// Used for the default text style for [Material].
   ///
@@ -339,7 +337,7 @@ class TextTheme with Diagnosticable {
     'This is the term used in the 2014 version of material design. The modern term is bodyText2. '
     'This feature was deprecated after v1.13.8.'
   )
-  TextStyle get body1 => bodyText2;
+  TextStyle? get body1 => bodyText2;
 
 
   /// Creates a copy of this text theme but with the given fields replaced with
@@ -383,69 +381,69 @@ class TextTheme with Diagnosticable {
   ///  * [merge] is used instead of [copyWith] when you want to merge all
   ///    of the fields of a TextTheme instead of individual fields.
   TextTheme copyWith({
-    TextStyle headline1,
-    TextStyle headline2,
-    TextStyle headline3,
-    TextStyle headline4,
-    TextStyle headline5,
-    TextStyle headline6,
-    TextStyle subtitle1,
-    TextStyle subtitle2,
-    TextStyle bodyText1,
-    TextStyle bodyText2,
-    TextStyle caption,
-    TextStyle button,
-    TextStyle overline,
+    TextStyle? headline1,
+    TextStyle? headline2,
+    TextStyle? headline3,
+    TextStyle? headline4,
+    TextStyle? headline5,
+    TextStyle? headline6,
+    TextStyle? subtitle1,
+    TextStyle? subtitle2,
+    TextStyle? bodyText1,
+    TextStyle? bodyText2,
+    TextStyle? caption,
+    TextStyle? button,
+    TextStyle? overline,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline1. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle display4,
+    TextStyle? display4,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline2. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle display3,
+    TextStyle? display3,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline3. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle display2,
+    TextStyle? display2,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline4. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle display1,
+    TextStyle? display1,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline5. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle headline,
+    TextStyle? headline,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is headline6. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle title,
+    TextStyle? title,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is subtitle1. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle subhead,
+    TextStyle? subhead,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is subtitle2. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle subtitle,
+    TextStyle? subtitle,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is bodyText1. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle body2,
+    TextStyle? body2,
     @Deprecated(
       'This is the term used in the 2014 version of material design. The modern term is bodyText2. '
       'This feature was deprecated after v1.13.8.'
     )
-    TextStyle body1,
+    TextStyle? body1,
   }) {
     assert(
       (headline1 == null && headline2 == null && headline3 == null && headline4 == null && headline5 == null && headline6 == null &&
@@ -522,7 +520,7 @@ class TextTheme with Diagnosticable {
   ///  * [copyWith] is used instead of [merge] when you wish to override
   ///    individual fields in the [TextTheme] instead of merging all of the
   ///    fields of two [TextTheme]s.
-  TextTheme merge(TextTheme other) {
+  TextTheme merge(TextTheme? other) {
     if (other == null)
       return this;
     return copyWith(
@@ -553,14 +551,14 @@ class TextTheme with Diagnosticable {
   /// the typography styles in the material design specification, as a starting
   /// point.
   TextTheme apply({
-    String fontFamily,
+    String? fontFamily,
     double fontSizeFactor = 1.0,
     double fontSizeDelta = 0.0,
-    Color displayColor,
-    Color bodyColor,
-    TextDecoration decoration,
-    Color decorationColor,
-    TextDecorationStyle decorationStyle,
+    Color? displayColor,
+    Color? bodyColor,
+    TextDecoration? decoration,
+    Color? decorationColor,
+    TextDecorationStyle? decorationStyle,
   }) {
     return TextTheme(
       headline1: headline1?.apply(
@@ -686,7 +684,7 @@ class TextTheme with Diagnosticable {
   /// Linearly interpolate between two text themes.
   ///
   /// {@macro dart.ui.shadow.lerp}
-  static TextTheme lerp(TextTheme a, TextTheme b, double t) {
+  static TextTheme lerp(TextTheme? a, TextTheme? b, double t) {
     assert(t != null);
     return TextTheme(
       headline1: TextStyle.lerp(a?.headline1, b?.headline1, t),

packages/flutter/lib/src/material/toggleable.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 'package:flutter/animation.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
@@ -32,15 +30,15 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// The [activeColor], and [inactiveColor] arguments must not be
   /// null. The [value] can only be null if tristate is true.
   RenderToggleable({
-    @required bool value,
+    required bool? value,
     bool tristate = false,
-    @required Color activeColor,
-    @required Color inactiveColor,
-    Color hoverColor,
-    Color focusColor,
-    ValueChanged<bool> onChanged,
-    BoxConstraints additionalConstraints,
-    @required TickerProvider vsync,
+    required Color activeColor,
+    required Color inactiveColor,
+    Color? hoverColor,
+    Color? focusColor,
+    ValueChanged<bool?>? onChanged,
+    required BoxConstraints additionalConstraints,
+    required TickerProvider vsync,
     bool hasFocus = false,
     bool hovering = false,
   }) : assert(tristate != null),
@@ -110,7 +108,7 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// animation reaches either 0.0 or 1.0.
   @protected
   AnimationController get positionController => _positionController;
-  AnimationController _positionController;
+  late AnimationController _positionController;
 
   /// The visual value of the control.
   ///
@@ -121,7 +119,7 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// to active (or vice versa), [value] is the target value and this animation
   /// gradually updates from 0.0 to 1.0 (or vice versa).
   CurvedAnimation get position => _position;
-  CurvedAnimation _position;
+  late CurvedAnimation _position;
 
   /// Used by subclasses to control the radial reaction animation.
   ///
@@ -132,8 +130,8 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// reaction.
   @protected
   AnimationController get reactionController => _reactionController;
-  AnimationController _reactionController;
-  Animation<double> _reaction;
+  late AnimationController _reactionController;
+  late Animation<double> _reaction;
 
   /// Used by subclasses to control the radial reaction's opacity animation for
   /// [hasFocus] changes.
@@ -146,8 +144,8 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// reaction.
   @protected
   AnimationController get reactionFocusFadeController => _reactionFocusFadeController;
-  AnimationController _reactionFocusFadeController;
-  Animation<double> _reactionFocusFade;
+  late AnimationController _reactionFocusFadeController;
+  late Animation<double> _reactionFocusFade;
 
   /// Used by subclasses to control the radial reaction's opacity animation for
   /// [hovering] changes.
@@ -160,8 +158,8 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// reaction.
   @protected
   AnimationController get reactionHoverFadeController => _reactionHoverFadeController;
-  AnimationController _reactionHoverFadeController;
-  Animation<double> _reactionHoverFade;
+  late AnimationController _reactionHoverFadeController;
+  late Animation<double> _reactionHoverFade;
 
   /// True if this toggleable has the input focus.
   bool get hasFocus => _hasFocus;
@@ -216,9 +214,9 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// When the value changes, this object starts the [positionController] and
   /// [position] animations to animate the visual appearance of the control to
   /// the new value.
-  bool get value => _value;
-  bool _value;
-  set value(bool value) {
+  bool? get value => _value;
+  bool? _value;
+  set value(bool? value) {
     assert(tristate || value != null);
     if (value == _value)
       return;
@@ -323,9 +321,9 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// that is displayed when the toggleable is toggled by a tap.
   ///
   /// Defaults to the [activeColor] at alpha [kRadialReactionAlpha].
-  Color get reactionColor => _reactionColor;
-  Color _reactionColor;
-  set reactionColor(Color value) {
+  Color? get reactionColor => _reactionColor;
+  Color? _reactionColor;
+  set reactionColor(Color? value) {
     assert(value != null);
     if (value == _reactionColor)
       return;
@@ -342,9 +340,9 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// callback is non-null. If the callback is null, then the control is
   /// disabled, and non-interactive. A disabled checkbox, for example, is
   /// displayed using a grey color and its value cannot be changed.
-  ValueChanged<bool> get onChanged => _onChanged;
-  ValueChanged<bool> _onChanged;
-  set onChanged(ValueChanged<bool> value) {
+  ValueChanged<bool?>? get onChanged => _onChanged;
+  ValueChanged<bool?>? _onChanged;
+  set onChanged(ValueChanged<bool?>? value) {
     if (value == _onChanged)
       return;
     final bool wasInteractive = isInteractive;
@@ -363,8 +361,8 @@ abstract class RenderToggleable extends RenderConstrainedBox {
   /// grey color and its value cannot be changed.
   bool get isInteractive => onChanged != null;
 
-  TapGestureRecognizer _tap;
-  Offset _downPosition;
+  late TapGestureRecognizer _tap;
+  Offset? _downPosition;
 
   @override
   void attach(PipelineOwner owner) {
@@ -410,13 +408,13 @@ abstract class RenderToggleable extends RenderConstrainedBox {
       return;
     switch (value) {
       case false:
-        onChanged(true);
+        onChanged!(true);
         break;
       case true:
-        onChanged(tristate ? null : false);
+        onChanged!(tristate ? null : false);
         break;
-      default: // case null:
-        onChanged(false);
+      case null:
+        onChanged!(false);
         break;
     }
     sendSemanticsEvent(const TapSemanticEvent());
@@ -457,8 +455,8 @@ abstract class RenderToggleable extends RenderConstrainedBox {
           Color.lerp(activeColor.withAlpha(kRadialReactionAlpha), hoverColor, _reactionHoverFade.value),
           focusColor,
           _reactionFocusFade.value,
-        );
-      final Offset center = Offset.lerp(_downPosition ?? origin, origin, _reaction.value);
+        )!;
+      final Offset center = Offset.lerp(_downPosition ?? origin, origin, _reaction.value)!;
       final double reactionRadius = hasFocus || hovering
           ? kRadialReactionRadius
           : _kRadialReactionRadiusTween.evaluate(_reaction);

packages/flutter/lib/src/material/typography.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 'package:flutter/foundation.dart';
 import 'package:flutter/painting.dart';
 
@@ -117,12 +115,12 @@ class Typography with Diagnosticable {
   /// The default values for [englishLike], [dense], and [tall] are
   /// [englishLike2014], [dense2014], and [tall2014].
   factory Typography.material2014({
-    TargetPlatform platform = TargetPlatform.android,
-    TextTheme black,
-    TextTheme white,
-    TextTheme englishLike,
-    TextTheme dense,
-    TextTheme tall,
+    TargetPlatform? platform = TargetPlatform.android,
+    TextTheme? black,
+    TextTheme? white,
+    TextTheme? englishLike,
+    TextTheme? dense,
+    TextTheme? tall,
   }) {
     assert(platform != null || (black != null && white != null));
     return Typography._withPlatform(
@@ -145,12 +143,12 @@ class Typography with Diagnosticable {
   /// The default values for [englishLike], [dense], and [tall] are
   /// [englishLike2018], [dense2018], and [tall2018].
   factory Typography.material2018({
-    TargetPlatform platform = TargetPlatform.android,
-    TextTheme black,
-    TextTheme white,
-    TextTheme englishLike,
-    TextTheme dense,
-    TextTheme tall,
+    TargetPlatform? platform = TargetPlatform.android,
+    TextTheme? black,
+    TextTheme? white,
+    TextTheme? englishLike,
+    TextTheme? dense,
+    TextTheme? tall,
   }) {
     assert(platform != null || (black != null && white != null));
     return Typography._withPlatform(
@@ -163,9 +161,9 @@ class Typography with Diagnosticable {
   }
 
   factory Typography._withPlatform(
-    TargetPlatform platform,
-    TextTheme black,
-    TextTheme white,
+    TargetPlatform? platform,
+    TextTheme? black,
+    TextTheme? white,
     TextTheme englishLike,
     TextTheme dense,
     TextTheme tall,
@@ -193,8 +191,10 @@ class Typography with Diagnosticable {
         black ??= blackHelsinki;
         white ??= whiteHelsinki;
         break;
+      case null:
+        break;
     }
-    return Typography._(black, white, englishLike, dense, tall);
+    return Typography._(black!, white!, englishLike, dense, tall);
   }
 
   const Typography._(this.black, this.white, this.englishLike, this.dense, this.tall)
@@ -269,17 +269,16 @@ class Typography with Diagnosticable {
       case ScriptCategory.tall:
         return tall;
     }
-    return null;
   }
 
   /// Creates a copy of this [Typography] with the given fields
   /// replaced by the non-null parameter values.
   Typography copyWith({
-    TextTheme black,
-    TextTheme white,
-    TextTheme englishLike,
-    TextTheme dense,
-    TextTheme tall,
+    TextTheme? black,
+    TextTheme? white,
+    TextTheme? englishLike,
+    TextTheme? dense,
+    TextTheme? tall,
   }) {
     return Typography._(
       black ?? this.black,