[NNBD] Migrating some Material tests (#67689)

packages/flutter/test/material/dialog_test.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';
 
 import 'package:flutter/material.dart';
@@ -13,7 +11,7 @@ import 'package:matcher/matcher.dart';
 
 import '../widgets/semantics_tester.dart';
 
-MaterialApp _buildAppWithDialog(Widget dialog, { ThemeData theme, double textScaleFactor = 1.0 }) {
+MaterialApp _buildAppWithDialog(Widget dialog, { ThemeData? theme, double textScaleFactor = 1.0 }) {
   return MaterialApp(
     theme: theme,
     home: Material(
@@ -27,7 +25,7 @@ MaterialApp _buildAppWithDialog(Widget dialog, { ThemeData theme, double textSca
                   context: context,
                   builder: (BuildContext context) {
                     return MediaQuery(
-                      data: MediaQuery.of(context).copyWith(textScaleFactor: textScaleFactor),
+                      data: MediaQuery.of(context)!.copyWith(textScaleFactor: textScaleFactor),
                       child: dialog,
                     );
                   },
@@ -46,7 +44,7 @@ Material _getMaterialFromDialog(WidgetTester tester) {
 }
 
 RenderParagraph _getTextRenderObjectFromDialog(WidgetTester tester, String text) {
-  return tester.element<StatelessElement>(find.descendant(of: find.byType(AlertDialog), matching: find.text(text))).renderObject as RenderParagraph;
+  return tester.element<StatelessElement>(find.descendant(of: find.byType(AlertDialog), matching: find.text(text))).renderObject! as RenderParagraph;
 }
 
 const ShapeBorder _defaultDialogShape = RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(4.0)));
@@ -276,7 +274,7 @@ void main() {
     );
 
     final Future<int> result = showDialog<int>(
-      context: navigator.currentContext,
+      context: navigator.currentContext!,
       builder: (BuildContext context) {
         return SimpleDialog(
           title: const Text('Title'),
@@ -678,73 +676,73 @@ void main() {
 
     void expectLeftEdgePadding(
       WidgetTester tester, {
-      Finder finder,
-      double textScaleFactor,
-      double unscaledValue,
+      required Finder finder,
+      required double textScaleFactor,
+      required double unscaledValue,
     }) {
       expect(
         tester.getTopLeft(dialogFinder).dx,
-        moreOrLessEquals(tester.getTopLeft(finder).dx - unscaledValue * paddingScaleFactors[textScaleFactor]),
+        moreOrLessEquals(tester.getTopLeft(finder).dx - unscaledValue * paddingScaleFactors[textScaleFactor]!),
       );
       expect(
         tester.getBottomLeft(dialogFinder).dx,
-        moreOrLessEquals(tester.getBottomLeft(finder).dx - unscaledValue * paddingScaleFactors[textScaleFactor]),
+        moreOrLessEquals(tester.getBottomLeft(finder).dx - unscaledValue * paddingScaleFactors[textScaleFactor]!),
       );
     }
 
     void expectRightEdgePadding(
       WidgetTester tester, {
-      Finder finder,
-      double textScaleFactor,
-      double unscaledValue,
+      required Finder finder,
+      required double textScaleFactor,
+      required double unscaledValue,
     }) {
       expect(
         tester.getTopRight(dialogFinder).dx,
-        moreOrLessEquals(tester.getTopRight(finder).dx + unscaledValue * paddingScaleFactors[textScaleFactor]),
+        moreOrLessEquals(tester.getTopRight(finder).dx + unscaledValue * paddingScaleFactors[textScaleFactor]!),
       );
       expect(
         tester.getBottomRight(dialogFinder).dx,
-        moreOrLessEquals(tester.getBottomRight(finder).dx + unscaledValue * paddingScaleFactors[textScaleFactor]),
+        moreOrLessEquals(tester.getBottomRight(finder).dx + unscaledValue * paddingScaleFactors[textScaleFactor]!),
       );
     }
 
     void expectTopEdgePadding(
       WidgetTester tester, {
-      Finder finder,
-      double textScaleFactor,
-      double unscaledValue,
+      required Finder finder,
+      required double textScaleFactor,
+      required double unscaledValue,
     }) {
       expect(
         tester.getTopLeft(dialogFinder).dy,
-        moreOrLessEquals(tester.getTopLeft(finder).dy - unscaledValue * paddingScaleFactors[textScaleFactor]),
+        moreOrLessEquals(tester.getTopLeft(finder).dy - unscaledValue * paddingScaleFactors[textScaleFactor]!),
       );
       expect(
         tester.getTopRight(dialogFinder).dy,
-        moreOrLessEquals(tester.getTopRight(finder).dy - unscaledValue * paddingScaleFactors[textScaleFactor]),
+        moreOrLessEquals(tester.getTopRight(finder).dy - unscaledValue * paddingScaleFactors[textScaleFactor]!),
       );
     }
 
     void expectBottomEdgePadding(
       WidgetTester tester, {
-      Finder finder,
-      double textScaleFactor,
-      double unscaledValue,
+      required Finder finder,
+      required double textScaleFactor,
+      required double unscaledValue,
     }) {
       expect(
         tester.getBottomLeft(dialogFinder).dy,
-        moreOrLessEquals(tester.getBottomRight(finder).dy + unscaledValue * paddingScaleFactors[textScaleFactor]),
+        moreOrLessEquals(tester.getBottomRight(finder).dy + unscaledValue * paddingScaleFactors[textScaleFactor]!),
       );
       expect(
         tester.getBottomRight(dialogFinder).dy,
-        moreOrLessEquals(tester.getBottomRight(finder).dy + unscaledValue * paddingScaleFactors[textScaleFactor]),
+        moreOrLessEquals(tester.getBottomRight(finder).dy + unscaledValue * paddingScaleFactors[textScaleFactor]!),
       );
     }
 
     void expectVerticalInnerPadding(
     WidgetTester tester, {
-      Finder top,
-      Finder bottom,
-      double value,
+      required Finder top,
+      required Finder bottom,
+      required double value,
     }) {
       expect(
         tester.getBottomLeft(top).dy,
@@ -1144,9 +1142,9 @@ void main() {
   });
 
   testWidgets('Dialogs removes MediaQuery padding and view insets', (WidgetTester tester) async {
-    BuildContext outerContext;
-    BuildContext routeContext;
-    BuildContext dialogContext;
+    late BuildContext outerContext;
+    late BuildContext routeContext;
+    late BuildContext dialogContext;
 
     await tester.pumpWidget(Localizations(
       locale: const Locale('en', 'US'),
@@ -1190,12 +1188,12 @@ void main() {
 
     await tester.pump();
 
-    expect(MediaQuery.of(outerContext).padding, const EdgeInsets.all(50.0));
-    expect(MediaQuery.of(routeContext).padding, EdgeInsets.zero);
-    expect(MediaQuery.of(dialogContext).padding, EdgeInsets.zero);
-    expect(MediaQuery.of(outerContext).viewInsets, const EdgeInsets.only(left: 25.0, bottom: 75.0));
-    expect(MediaQuery.of(routeContext).viewInsets, const EdgeInsets.only(left: 25.0, bottom: 75.0));
-    expect(MediaQuery.of(dialogContext).viewInsets, EdgeInsets.zero);
+    expect(MediaQuery.of(outerContext)!.padding, const EdgeInsets.all(50.0));
+    expect(MediaQuery.of(routeContext)!.padding, EdgeInsets.zero);
+    expect(MediaQuery.of(dialogContext)!.padding, EdgeInsets.zero);
+    expect(MediaQuery.of(outerContext)!.viewInsets, const EdgeInsets.only(left: 25.0, bottom: 75.0));
+    expect(MediaQuery.of(routeContext)!.viewInsets, const EdgeInsets.only(left: 25.0, bottom: 75.0));
+    expect(MediaQuery.of(dialogContext)!.viewInsets, EdgeInsets.zero);
   });
 
   testWidgets('Dialog widget insets by viewInsets', (WidgetTester tester) async {
@@ -1386,7 +1384,7 @@ void main() {
     // Dismiss is confirmed IFF confirmDismiss() returns true.
     Future<bool> confirmDismiss (DismissDirection dismissDirection) {
       return showDialog<bool>(
-        context: _scaffoldKey.currentContext,
+        context: _scaffoldKey.currentContext!,
         barrierDismissible: true, // showDialog() returns null if tapped outside the dialog
         builder: (BuildContext context) {
           return AlertDialog(
@@ -1551,11 +1549,11 @@ void main() {
   testWidgets('showDialog safe area', (WidgetTester tester) async {
     await tester.pumpWidget(
       MaterialApp(
-        builder: (BuildContext context, Widget child) {
+        builder: (BuildContext context, Widget? child) {
           return MediaQuery(
             // Set up the safe area to be 20 pixels in from each side
             data: const MediaQueryData(padding: EdgeInsets.all(20.0)),
-            child: child,
+            child: child!,
           );
         },
         home: const Center(child: Text('Test')),
@@ -1741,13 +1739,13 @@ void main() {
   });
 
   testWidgets('Dialog with RouteSettings', (WidgetTester tester) async {
-    RouteSettings currentRouteSetting;
+    late RouteSettings currentRouteSetting;
 
     await tester.pumpWidget(
       MaterialApp(
         navigatorObservers: <NavigatorObserver>[
           _ClosureNavigatorObserver(onDidChange: (Route<dynamic> newRoute) {
-            currentRouteSetting = newRoute?.settings;
+            currentRouteSetting = newRoute.settings;
           })
         ],
         home: const Material(
@@ -1773,7 +1771,7 @@ void main() {
             SimpleDialogOption(
               child: const Text('X'),
               onPressed: () {
-                Navigator.of(context).pop();
+                Navigator.of(context)!.pop();
               },
             ),
           ],
@@ -1791,7 +1789,7 @@ void main() {
 
     expect(await result, isNull);
     await tester.pumpAndSettle();
-    expect(currentRouteSetting?.name, '/');
+    expect(currentRouteSetting.name, '/');
   });
 }
 
@@ -1799,7 +1797,7 @@ class DialogObserver extends NavigatorObserver {
   int dialogCount = 0;
 
   @override
-  void didPush(Route<dynamic> route, Route<dynamic> previousRoute) {
+  void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) {
     if (route.toString().contains('_DialogRoute')) {
       dialogCount++;
     }
@@ -1808,19 +1806,19 @@ class DialogObserver extends NavigatorObserver {
 }
 
 class _ClosureNavigatorObserver extends NavigatorObserver {
-  _ClosureNavigatorObserver({@required this.onDidChange});
+  _ClosureNavigatorObserver({required this.onDidChange});
 
   final void Function(Route<dynamic> newRoute) onDidChange;
 
   @override
-  void didPush(Route<dynamic> route, Route<dynamic> previousRoute) => onDidChange(route);
+  void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) => onDidChange(route);
 
   @override
-  void didPop(Route<dynamic> route, Route<dynamic> previousRoute) => onDidChange(previousRoute);
+  void didPop(Route<dynamic> route, Route<dynamic>? previousRoute) => onDidChange(previousRoute!);
 
   @override
-  void didRemove(Route<dynamic> route, Route<dynamic> previousRoute) => onDidChange(previousRoute);
+  void didRemove(Route<dynamic> route, Route<dynamic>? previousRoute) => onDidChange(previousRoute!);
 
   @override
-  void didReplace({Route<dynamic> newRoute, Route<dynamic> oldRoute}) => onDidChange(newRoute);
+  void didReplace({Route<dynamic>? newRoute, Route<dynamic>? oldRoute}) => onDidChange(newRoute!);
 }

packages/flutter/test/material/dialog_theme_test.dart

@@ -2,13 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-MaterialApp _appWithDialog(WidgetTester tester, Widget dialog, { ThemeData theme }) {
+MaterialApp _appWithDialog(WidgetTester tester, Widget dialog, { ThemeData? theme }) {
   return MaterialApp(
     theme: theme,
     home: Material(
@@ -40,7 +38,7 @@ Material _getMaterialFromDialog(WidgetTester tester) {
 }
 
 RenderParagraph _getTextRenderObject(WidgetTester tester, String text) {
-  return tester.element<StatelessElement>(find.text(text)).renderObject as RenderParagraph;
+  return tester.element<StatelessElement>(find.text(text)).renderObject! as RenderParagraph;
 }
 
 void main() {
@@ -184,7 +182,7 @@ void main() {
     await tester.pumpAndSettle();
 
     final RenderParagraph title = _getTextRenderObject(tester, titleText);
-    expect(title.text.style.color, titleTextStyle.color);
+    expect(title.text.style!.color, titleTextStyle.color);
   });
 
   testWidgets('Simple Dialog - Custom Title Text Style - Constructor Param', (WidgetTester tester) async {
@@ -232,7 +230,7 @@ void main() {
     await tester.pumpAndSettle();
 
     final RenderParagraph title = _getTextRenderObject(tester, titleText);
-    expect(title.text.style.color, titleTextStyle.color);
+    expect(title.text.style!.color, titleTextStyle.color);
   });
 
   testWidgets('Custom Content Text Style - Constructor Param', (WidgetTester tester) async {
@@ -283,6 +281,6 @@ void main() {
     await tester.pumpAndSettle();
 
     final RenderParagraph content = _getTextRenderObject(tester, contentText);
-    expect(content.text.style.color, contentTextStyle.color);
+    expect(content.text.style!.color, contentTextStyle.color);
   });
 }

packages/flutter/test/material/divider_test.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/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/painting.dart';
@@ -22,8 +20,8 @@ void main() {
     final RenderBox box = tester.firstRenderObject(find.byType(Divider));
     expect(box.size.height, 16.0);
     final Container container = tester.widget(find.byType(Container));
-    final BoxDecoration decoration = container.decoration as BoxDecoration;
-    expect(decoration.border.bottom.width, 0.0);
+    final BoxDecoration decoration = container.decoration! as BoxDecoration;
+    expect(decoration.border!.bottom.width, 0.0);
   });
 
   testWidgets('Divider custom thickness', (WidgetTester tester) async {
@@ -38,8 +36,8 @@ void main() {
       ),
     );
     final Container container = tester.widget(find.byType(Container));
-    final BoxDecoration decoration = container.decoration as BoxDecoration;
-    expect(decoration.border.bottom.width, 5.0);
+    final BoxDecoration decoration = container.decoration! as BoxDecoration;
+    expect(decoration.border!.bottom.width, 5.0);
   });
 
   testWidgets('Horizontal divider custom indentation', (WidgetTester tester) async {
@@ -107,8 +105,8 @@ void main() {
     final RenderBox box = tester.firstRenderObject(find.byType(VerticalDivider));
     expect(box.size.width, 16.0);
     final Container container = tester.widget(find.byType(Container));
-    final BoxDecoration decoration = container.decoration as BoxDecoration;
-    final Border border = decoration.border as Border;
+    final BoxDecoration decoration = container.decoration! as BoxDecoration;
+    final Border border = decoration.border! as Border;
     expect(border.left.width, 0.0);
   });
 
@@ -124,8 +122,8 @@ void main() {
       ),
     );
     final Container container = tester.widget(find.byType(Container));
-    final BoxDecoration decoration = container.decoration as BoxDecoration;
-    final Border border = decoration.border as Border;
+    final BoxDecoration decoration = container.decoration! as BoxDecoration;
+    final Border border = decoration.border! as Border;
     expect(border.left.width, 5.0);
   });
 

packages/flutter/test/material/divider_theme_test.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/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -71,11 +69,11 @@ void main() {
       expect(box.size.height, 16.0);
 
       final Container container = tester.widget(find.byType(Container));
-      final BoxDecoration decoration = container.decoration as BoxDecoration;
-      expect(decoration.border.bottom.width, 0.0);
+      final BoxDecoration decoration = container.decoration! as BoxDecoration;
+      expect(decoration.border!.bottom.width, 0.0);
 
       final ThemeData theme = ThemeData();
-      expect(decoration.border.bottom.color, theme.dividerColor);
+      expect(decoration.border!.bottom.color, theme.dividerColor);
 
       final Rect dividerRect = tester.getRect(find.byType(Divider));
       final Rect lineRect = tester.getRect(find.byType(DecoratedBox));
@@ -96,14 +94,14 @@ void main() {
       expect(box.size.height, dividerTheme.space);
 
       final Container container = tester.widget(find.byType(Container));
-      final BoxDecoration decoration = container.decoration as BoxDecoration;
-      expect(decoration.border.bottom.width, dividerTheme.thickness);
-      expect(decoration.border.bottom.color, dividerTheme.color);
+      final BoxDecoration decoration = container.decoration! as BoxDecoration;
+      expect(decoration.border!.bottom.width, dividerTheme.thickness);
+      expect(decoration.border!.bottom.color, dividerTheme.color);
 
       final Rect dividerRect = tester.getRect(find.byType(Divider));
       final Rect lineRect = tester.getRect(find.byType(DecoratedBox));
-      expect(lineRect.left, dividerRect.left + dividerTheme.indent);
-      expect(lineRect.right, dividerRect.right - dividerTheme.endIndent);
+      expect(lineRect.left, dividerRect.left + dividerTheme.indent!);
+      expect(lineRect.right, dividerRect.right - dividerTheme.endIndent!);
     });
 
     testWidgets('Widget properties take priority over theme', (WidgetTester tester) async {
@@ -131,9 +129,9 @@ void main() {
       expect(box.size.height, height);
 
       final Container container = tester.widget(find.byType(Container));
-      final BoxDecoration decoration = container.decoration as BoxDecoration;
-      expect(decoration.border.bottom.width, thickness);
-      expect(decoration.border.bottom.color, color);
+      final BoxDecoration decoration = container.decoration! as BoxDecoration;
+      expect(decoration.border!.bottom.width, thickness);
+      expect(decoration.border!.bottom.color, color);
 
       final Rect dividerRect = tester.getRect(find.byType(Divider));
       final Rect lineRect = tester.getRect(find.byType(DecoratedBox));
@@ -154,8 +152,8 @@ void main() {
       expect(box.size.width, 16.0);
 
       final Container container = tester.widget(find.byType(Container));
-      final BoxDecoration decoration = container.decoration as BoxDecoration;
-      final Border border = decoration.border as Border;
+      final BoxDecoration decoration = container.decoration! as BoxDecoration;
+      final Border border = decoration.border! as Border;
       expect(border.left.width, 0.0);
 
       final ThemeData theme = ThemeData();
@@ -180,15 +178,15 @@ void main() {
       expect(box.size.width, dividerTheme.space);
 
       final Container container = tester.widget(find.byType(Container));
-      final BoxDecoration decoration = container.decoration as BoxDecoration;
-      final Border border = decoration.border as Border;
+      final BoxDecoration decoration = container.decoration! as BoxDecoration;
+      final Border border = decoration.border! as Border;
       expect(border.left.width, dividerTheme.thickness);
       expect(border.left.color, dividerTheme.color);
 
       final Rect dividerRect = tester.getRect(find.byType(VerticalDivider));
       final Rect lineRect = tester.getRect(find.byType(DecoratedBox));
-      expect(lineRect.top, dividerRect.top + dividerTheme.indent);
-      expect(lineRect.bottom, dividerRect.bottom - dividerTheme.endIndent);
+      expect(lineRect.top, dividerRect.top + dividerTheme.indent!);
+      expect(lineRect.bottom, dividerRect.bottom - dividerTheme.endIndent!);
     });
 
     testWidgets('Widget properties take priority over theme', (WidgetTester tester) async {
@@ -216,8 +214,8 @@ void main() {
       expect(box.size.width, width);
 
       final Container container = tester.widget(find.byType(Container));
-      final BoxDecoration decoration = container.decoration as BoxDecoration;
-      final Border border = decoration.border as Border;
+      final BoxDecoration decoration = container.decoration! as BoxDecoration;
+      final Border border = decoration.border! as Border;
       expect(border.left.width, thickness);
       expect(border.left.color, color);
 

packages/flutter/test/material/drawer_test.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/rendering.dart';
 import 'package:flutter/material.dart';
@@ -126,7 +124,7 @@ void main() {
     }
 
     final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();
-    Widget buildFrame({ Color drawerScrimColor }) {
+    Widget buildFrame({ Color? drawerScrimColor }) {
       return MaterialApp(
         home: Scaffold(
           key: scaffoldKey,
@@ -147,7 +145,7 @@ void main() {
     // Default drawerScrimColor
 
     await tester.pumpWidget(buildFrame(drawerScrimColor: null));
-    scaffoldKey.currentState.openDrawer();
+    scaffoldKey.currentState!.openDrawer();
     await tester.pumpAndSettle();
 
     expect(getScrim().color, Colors.black54);
@@ -159,7 +157,7 @@ void main() {
     // Specific drawerScrimColor
 
     await tester.pumpWidget(buildFrame(drawerScrimColor: const Color(0xFF323232)));
-    scaffoldKey.currentState.openDrawer();
+    scaffoldKey.currentState!.openDrawer();
     await tester.pumpAndSettle();
 
     expect(getScrim().color, const Color(0xFF323232));

packages/flutter/test/material/dropdown_form_field_test.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 window;
 
@@ -14,7 +12,7 @@ import 'package:flutter/rendering.dart';
 import '../rendering/mock_canvas.dart';
 
 const List<String> menuItems = <String>['one', 'two', 'three', 'four'];
-final ValueChanged<String> onChanged = (_) { };
+final ValueChanged<String?> onChanged = (_) { };
 final Type dropdownButtonType = DropdownButton<String>(
   onChanged: (_) { },
   items: const <DropdownMenuItem<String>>[],
@@ -28,22 +26,22 @@ Finder _iconRichText(Key iconKey) {
 }
 
 Widget buildFormFrame({
-  Key buttonKey,
+  Key? buttonKey,
   AutovalidateMode autovalidateMode = AutovalidateMode.disabled,
   int elevation = 8,
-  String value = 'two',
-  ValueChanged<String> onChanged,
-  VoidCallback onTap,
-  Widget icon,
-  Color iconDisabledColor,
-  Color iconEnabledColor,
+  String? value = 'two',
+  ValueChanged<String?>? onChanged,
+  VoidCallback? onTap,
+  Widget? icon,
+  Color? iconDisabledColor,
+  Color? iconEnabledColor,
   double iconSize = 24.0,
   bool isDense = true,
   bool isExpanded = false,
-  Widget hint,
-  Widget disabledHint,
-  Widget underline,
-  List<String> items = menuItems,
+  Widget? hint,
+  Widget? disabledHint,
+  Widget? underline,
+  List<String>? items = menuItems,
   Alignment alignment = Alignment.center,
   TextDirection textDirection = TextDirection.ltr,
 }) {
@@ -112,15 +110,15 @@ class _TestAppState extends State<TestApp> {
 
 class TestApp extends StatefulWidget {
   const TestApp({
-    Key key,
-    this.textDirection,
-    this.child,
+    Key? key,
+    required this.textDirection,
+    required this.child,
     this.mediaSize,
   }) : super(key: key);
 
   final TextDirection textDirection;
   final Widget child;
-  final Size mediaSize;
+  final Size? mediaSize;
 
   @override
   _TestAppState createState() => _TestAppState();
@@ -129,7 +127,7 @@ class TestApp extends StatefulWidget {
 void verifyPaintedShadow(Finder customPaint, int elevation) {
   const Rect originalRectangle = Rect.fromLTRB(0.0, 0.0, 800, 208.0);
 
-  final List<BoxShadow> boxShadows = List<BoxShadow>.generate(3, (int index) => kElevationToShadow[elevation][index]);
+  final List<BoxShadow> boxShadows = List<BoxShadow>.generate(3, (int index) => kElevationToShadow[elevation]![index]);
   final List<RRect> rrects = List<RRect>.generate(3, (int index) {
     return RRect.fromRectAndRadius(
       originalRectangle.shift(
@@ -151,7 +149,7 @@ void verifyPaintedShadow(Finder customPaint, int elevation) {
 
 void main() {
   testWidgets('DropdownButtonFormField with autovalidation test', (WidgetTester tester) async {
-    String value = 'one';
+    String? value = 'one';
     int _validateCalled = 0;
 
     await tester.pumpWidget(
@@ -171,12 +169,12 @@ void main() {
                     child: Text(value),
                   );
                 }).toList(),
-                onChanged: (String newValue) {
+                onChanged: (String? newValue) {
                   setState(() {
                     value = newValue;
                   });
                 },
-                validator: (String currentValue) {
+                validator: (String? currentValue) {
                   _validateCalled++;
                   return currentValue == null ? 'Must select value' : null;
                 },
@@ -340,14 +338,14 @@ void main() {
       ),
     );
 
-    expect(richText.text.style.color, Colors.amber);
-    expect(richText.text.style.fontSize, 20.0);
+    expect(richText.text.style!.color, Colors.amber);
+    expect(richText.text.style!.fontSize, 20.0);
   });
 
   testWidgets('DropdownButtonFormField - disabledHint displays when the items list is empty, when items is null', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
 
-    Widget build({ List<String> items }){
+    Widget build({ List<String>? items }){
       return buildFormFrame(
         items: items,
         buttonKey: buttonKey,
@@ -373,7 +371,7 @@ void main() {
     (WidgetTester tester) async {
       final Key buttonKey = UniqueKey();
 
-      Widget build({ List<String> items }){
+      Widget build({ List<String>? items }){
         return buildFormFrame(
           items: items,
           buttonKey: buttonKey,
@@ -395,7 +393,7 @@ void main() {
   testWidgets('DropdownButtonFormField - disabledHint is null by default', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
 
-    Widget build({ List<String> items }){
+    Widget build({ List<String>? items }){
       return buildFormFrame(
         items: items,
         buttonKey: buttonKey,
@@ -415,7 +413,7 @@ void main() {
   testWidgets('DropdownButtonFormField - disabledHint is null by default', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
 
-    Widget build({ List<String> items }){
+    Widget build({ List<String>? items }){
       return buildFormFrame(
         items: items,
         buttonKey: buttonKey,
@@ -435,7 +433,7 @@ void main() {
   testWidgets('DropdownButtonFormField - disabledHint displays when onChanged is null', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
 
-    Widget build({ List<String> items, ValueChanged<String> onChanged }){
+    Widget build({ List<String>? items, ValueChanged<String?>? onChanged }){
       return buildFormFrame(
         items: items,
         buttonKey: buttonKey,
@@ -453,7 +451,7 @@ void main() {
   testWidgets('DropdownButtonFormField - disabled hint should be of same size as enabled hint', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
 
-    Widget build({ List<String> items}){
+    Widget build({ List<String>? items}){
       return buildFormFrame(
         items: items,
         buttonKey: buttonKey,
@@ -493,7 +491,7 @@ void main() {
 
     // test for enabled color
     final RichText enabledRichText = tester.widget<RichText>(_iconRichText(iconKey));
-    expect(enabledRichText.text.style.color, Colors.pink);
+    expect(enabledRichText.text.style!.color, Colors.pink);
 
     // test for disabled color
     await tester.pumpWidget(buildFormFrame(
@@ -505,7 +503,7 @@ void main() {
     ));
 
     final RichText disabledRichText = tester.widget<RichText>(_iconRichText(iconKey));
-    expect(disabledRichText.text.style.color, Colors.orange);
+    expect(disabledRichText.text.style!.color, Colors.orange);
   });
 
   testWidgets('DropdownButtonFormField - default elevation', (WidgetTester tester) async {
@@ -583,7 +581,7 @@ void main() {
           home: Scaffold(
             body: DropdownButtonFormField<String>(
               value: 'c',
-              onChanged: (String newValue) {},
+              onChanged: (String? newValue) {},
               items: itemsWithDuplicateValues,
             ),
           ),
@@ -614,7 +612,7 @@ void main() {
           home: Scaffold(
             body: DropdownButton<String>(
               value: 'e',
-              onChanged: (String newValue) {},
+              onChanged: (String? newValue) {},
               items: itemsWithDuplicateValues,
             ),
           ),
@@ -636,7 +634,7 @@ void main() {
       'Two',
       'Three',
     ];
-    String selectedItem = items[0];
+    String? selectedItem = items[0];
 
     await tester.pumpWidget(
       StatefulBuilder(
@@ -645,7 +643,7 @@ void main() {
             home: Scaffold(
               body: DropdownButtonFormField<String>(
                 value: selectedItem,
-                onChanged: (String string) => setState(() => selectedItem = string),
+                onChanged: (String? string) => setState(() => selectedItem = string),
                 selectedItemBuilder: (BuildContext context) {
                   int index = 0;
                   return items.map((String string) {
@@ -676,8 +674,10 @@ void main() {
 
   testWidgets('DropdownButton onTap callback is called when defined', (WidgetTester tester) async {
     int dropdownButtonTapCounter = 0;
-    String value = 'one';
-    void onChanged(String newValue) { value = newValue; }
+    String? value = 'one';
+    void onChanged(String? newValue) {
+      value = newValue;
+    }
     void onTap() { dropdownButtonTapCounter += 1; }
 
     Widget build() => buildFormFrame(
@@ -780,7 +780,7 @@ void main() {
                 );
               }).toList(),
               onChanged: onChanged,
-              validator: (String value) {
+              validator: (String? value) {
                 _validateCalled++;
                 return null;
               },

packages/flutter/test/material/dropdown_test.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 window;
 
@@ -18,7 +16,7 @@ import '../rendering/mock_canvas.dart';
 import '../widgets/semantics_tester.dart';
 
 const List<String> menuItems = <String>['one', 'two', 'three', 'four'];
-final ValueChanged<String> onChanged = (_) { };
+final ValueChanged<String?> onChanged = (_) { };
 
 final Type dropdownButtonType = DropdownButton<String>(
   onChanged: (_) { },
@@ -33,32 +31,32 @@ Finder _iconRichText(Key iconKey) {
 }
 
 Widget buildDropdown({
-    bool isFormField,
-    Key buttonKey,
-    String value = 'two',
-    ValueChanged<String> onChanged,
-    VoidCallback onTap,
-    Widget icon,
-    Color iconDisabledColor,
-    Color iconEnabledColor,
+    required bool isFormField,
+    Key? buttonKey,
+    String? value = 'two',
+    ValueChanged<String?>? onChanged,
+    VoidCallback? onTap,
+    Widget? icon,
+    Color? iconDisabledColor,
+    Color? iconEnabledColor,
     double iconSize = 24.0,
     bool isDense = false,
     bool isExpanded = false,
-    Widget hint,
-    Widget disabledHint,
-    Widget underline,
-    List<String> items = menuItems,
-    List<Widget> Function(BuildContext) selectedItemBuilder,
-    double itemHeight = kMinInteractiveDimension,
+    Widget? hint,
+    Widget? disabledHint,
+    Widget? underline,
+    List<String>? items = menuItems,
+    List<Widget> Function(BuildContext)? selectedItemBuilder,
+    double? itemHeight = kMinInteractiveDimension,
     Alignment alignment = Alignment.center,
     TextDirection textDirection = TextDirection.ltr,
-    Size mediaSize,
-    FocusNode focusNode,
+    Size? mediaSize,
+    FocusNode? focusNode,
     bool autofocus = false,
-    Color focusColor,
-    Color dropdownColor,
+    Color? focusColor,
+    Color? dropdownColor,
   }) {
-  final List<DropdownMenuItem<String>> listItems = items == null
+  final List<DropdownMenuItem<String>>? listItems = items == null
       ? null
       : items.map<DropdownMenuItem<String>>((String item) {
     return DropdownMenuItem<String>(
@@ -119,29 +117,29 @@ Widget buildDropdown({
 }
 
 Widget buildFrame({
-  Key buttonKey,
-  String value = 'two',
-  ValueChanged<String> onChanged,
-  VoidCallback onTap,
-  Widget icon,
-  Color iconDisabledColor,
-  Color iconEnabledColor,
+  Key? buttonKey,
+  String? value = 'two',
+  ValueChanged<String?>? onChanged,
+  VoidCallback? onTap,
+  Widget? icon,
+  Color? iconDisabledColor,
+  Color? iconEnabledColor,
   double iconSize = 24.0,
   bool isDense = false,
   bool isExpanded = false,
-  Widget hint,
-  Widget disabledHint,
-  Widget underline,
-  List<String> items = menuItems,
-  List<Widget> Function(BuildContext) selectedItemBuilder,
-  double itemHeight = kMinInteractiveDimension,
+  Widget? hint,
+  Widget? disabledHint,
+  Widget? underline,
+  List<String>? items = menuItems,
+  List<Widget> Function(BuildContext)? selectedItemBuilder,
+  double? itemHeight = kMinInteractiveDimension,
   Alignment alignment = Alignment.center,
   TextDirection textDirection = TextDirection.ltr,
-  Size mediaSize,
-  FocusNode focusNode,
+  Size? mediaSize,
+  FocusNode? focusNode,
   bool autofocus = false,
-  Color focusColor,
-  Color dropdownColor,
+  Color? focusColor,
+  Color? dropdownColor,
   bool isFormField = false,
 }) {
   return TestApp(
@@ -181,15 +179,15 @@ Widget buildFrame({
 
 class TestApp extends StatefulWidget {
   const TestApp({
-    Key key,
-    this.textDirection,
-    this.child,
+    Key? key,
+    required this.textDirection,
+    required this.child,
     this.mediaSize,
   }) : super(key: key);
 
   final TextDirection textDirection;
   final Widget child;
-  final Size mediaSize;
+  final Size? mediaSize;
 
   @override
   _TestAppState createState() => _TestAppState();
@@ -239,7 +237,7 @@ void checkSelectedItemTextGeometry(WidgetTester tester, String value) {
 void verifyPaintedShadow(Finder customPaint, int elevation) {
   const Rect originalRectangle = Rect.fromLTRB(0.0, 0.0, 800, 208.0);
 
-  final List<BoxShadow> boxShadows = List<BoxShadow>.generate(3, (int index) => kElevationToShadow[elevation][index]);
+  final List<BoxShadow> boxShadows = List<BoxShadow>.generate(3, (int index) => kElevationToShadow[elevation]![index]);
   final List<RRect> rrects = List<RRect>.generate(3, (int index) {
     return RRect.fromRectAndRadius(
       originalRectangle.shift(
@@ -259,7 +257,7 @@ void verifyPaintedShadow(Finder customPaint, int elevation) {
   );
 }
 
-Future<void> checkDropdownColor(WidgetTester tester, {Color color, bool isFormField = false }) async {
+Future<void> checkDropdownColor(WidgetTester tester, {Color? color, bool isFormField = false }) async {
   const String text = 'foo';
   await tester.pumpWidget(
     MaterialApp(
@@ -340,8 +338,8 @@ void main() {
   });
 
   testWidgets('Dropdown button control test', (WidgetTester tester) async {
-    String value = 'one';
-    void didChangeValue(String newValue) {
+    String? value = 'one';
+    void didChangeValue(String? newValue) {
       value = newValue;
     }
 
@@ -379,8 +377,8 @@ void main() {
   });
 
   testWidgets('Dropdown button with no app', (WidgetTester tester) async {
-    String value = 'one';
-    void didChangeValue(String newValue) {
+    String? value = 'one';
+    void didChangeValue(String? newValue) {
       value = newValue;
     }
 
@@ -449,7 +447,7 @@ void main() {
           home: Scaffold(
             body: DropdownButton<String>(
               value: 'c',
-              onChanged: (String newValue) {},
+              onChanged: (String? newValue) {},
               items: itemsWithDuplicateValues,
             ),
           ),
@@ -480,7 +478,7 @@ void main() {
           home: Scaffold(
             body: DropdownButton<String>(
               value: 'e',
-              onChanged: (String newValue) {},
+              onChanged: (String? newValue) {},
               items: itemsWithDuplicateValues,
             ),
           ),
@@ -499,7 +497,7 @@ void main() {
   testWidgets('Dropdown form field uses form field state', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
     final GlobalKey<FormState> formKey = GlobalKey<FormState>();
-    String value;
+    String? value;
     await tester.pumpWidget(
         StatefulBuilder(
             builder: (BuildContext context, StateSetter setState) {
@@ -520,9 +518,9 @@ void main() {
                             child: Text(val)
                         );
                       }).toList(),
-                      validator: (String v) => v == null ? 'Must select value' : null,
-                      onChanged: (String newValue) {},
-                      onSaved: (String v) {
+                      validator: (String? v) => v == null ? 'Must select value' : null,
+                      onChanged: (String? newValue) {},
+                      onSaved: (String? v) {
                         setState(() {
                           value = v;
                         });
@@ -536,7 +534,7 @@ void main() {
     );
     int getIndex() {
       final IndexedStack stack = tester.element(find.byType(IndexedStack)).widget as IndexedStack;
-      return stack.index;
+      return stack.index!;
     }
     // Initial value of null displays hint
     expect(value, equals(null));
@@ -548,7 +546,7 @@ void main() {
     expect(getIndex(), 2);
     // Changes only made to FormField state until form saved
     expect(value, equals(null));
-    final FormState form = formKey.currentState;
+    final FormState form = formKey.currentState!;
     form.save();
     expect(value, equals('three'));
   });
@@ -589,12 +587,12 @@ void main() {
   });
 
   testWidgets('Dropdown screen edges', (WidgetTester tester) async {
-    int value = 4;
+    int? value = 4;
     final List<DropdownMenuItem<int>> items = <DropdownMenuItem<int>>[
       for (int i = 0; i < 20; ++i) DropdownMenuItem<int>(value: i, child: Text('$i')),
     ];
 
-    void handleChanged(int newValue) {
+    void handleChanged(int? newValue) {
       value = newValue;
     }
 
@@ -748,7 +746,7 @@ void main() {
 
     // test for enabled color
     final RichText enabledRichText = tester.widget<RichText>(_iconRichText(iconKey));
-    expect(enabledRichText.text.style.color, Colors.grey.shade700);
+    expect(enabledRichText.text.style!.color, Colors.grey.shade700);
 
     // test for disabled color
     await tester.pumpWidget(buildFrame(
@@ -757,7 +755,7 @@ void main() {
     ));
 
     final RichText disabledRichText = tester.widget<RichText>(_iconRichText(iconKey));
-    expect(disabledRichText.text.style.color, Colors.grey.shade400);
+    expect(disabledRichText.text.style!.color, Colors.grey.shade400);
   });
 
   testWidgets('Dropdown button icon should have the passed in size and color instead of defaults', (WidgetTester tester) async {
@@ -778,7 +776,7 @@ void main() {
 
     // test for enabled color
     final RichText enabledRichText = tester.widget<RichText>(_iconRichText(iconKey));
-    expect(enabledRichText.text.style.color, Colors.pink);
+    expect(enabledRichText.text.style!.color, Colors.pink);
 
     // test for disabled color
     await tester.pumpWidget(buildFrame(
@@ -790,7 +788,7 @@ void main() {
     ));
 
     final RichText disabledRichText = tester.widget<RichText>(_iconRichText(iconKey));
-    expect(disabledRichText.text.style.color, Colors.orange);
+    expect(disabledRichText.text.style!.color, Colors.orange);
   });
 
   testWidgets('Dropdown button should use its own size and color properties over those defined by the theme', (WidgetTester tester) async {
@@ -817,7 +815,7 @@ void main() {
 
     // test for enabled color
     final RichText enabledRichText = tester.widget<RichText>(_iconRichText(iconKey));
-    expect(enabledRichText.text.style.color, Colors.yellow);
+    expect(enabledRichText.text.style!.color, Colors.yellow);
 
     // test for disabled color
     await tester.pumpWidget(buildFrame(
@@ -829,7 +827,7 @@ void main() {
     ));
 
     final RichText disabledRichText = tester.widget<RichText>(_iconRichText(iconKey));
-    expect(disabledRichText.text.style.color, Colors.yellow);
+    expect(disabledRichText.text.style!.color, Colors.yellow);
   });
 
   testWidgets('Dropdown button with isDense:true aligns selected menu item', (WidgetTester tester) async {
@@ -950,7 +948,7 @@ void main() {
 
   testWidgets('Size of DropdownButton with null value', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
-    String value;
+    String? value;
 
     Widget build() => buildFrame(buttonKey: buttonKey, value: value, onChanged: onChanged);
 
@@ -972,7 +970,7 @@ void main() {
   testWidgets('Size of DropdownButton with no items', (WidgetTester tester) async {
     // Regression test for https://github.com/flutter/flutter/issues/26419
     final Key buttonKey = UniqueKey();
-    List<String> items;
+    List<String>? items;
 
     Widget build() => buildFrame(buttonKey: buttonKey, items: items, onChanged: onChanged);
 
@@ -998,9 +996,9 @@ void main() {
 
   testWidgets('Layout of a DropdownButton with null value', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
-    String value;
+    String? value;
 
-    void onChanged(String newValue) {
+    void onChanged(String? newValue) {
       value = newValue;
     }
 
@@ -1026,7 +1024,7 @@ void main() {
 
   testWidgets('Size of DropdownButton with null value and a hint', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
-    String value;
+    String? value;
 
     // The hint will define the dropdown's width
     Widget build() => buildFrame(buttonKey: buttonKey, value: value, hint: const Text('onetwothree'));
@@ -1052,10 +1050,10 @@ void main() {
     // The dropdown menu isn't readily accessible. To find it we're assuming that it
     // contains a ListView and that it's an instance of _DropdownMenu.
     Rect getMenuRect() {
-      Rect menuRect;
+      late Rect menuRect;
       tester.element(find.byType(ListView)).visitAncestorElements((Element element) {
         if (element.toString().startsWith('_DropdownMenu')) {
-          final RenderBox box = element.findRenderObject() as RenderBox;
+          final RenderBox box = element.findRenderObject()! as RenderBox;
           assert(box != null);
           menuRect = box.localToGlobal(Offset.zero) & box.size;
           return false;
@@ -1077,8 +1075,8 @@ void main() {
       return buttonPadding.inflateRect(buttonRect);
     }
 
-    Rect buttonRect;
-    Rect menuRect;
+    late Rect buttonRect;
+    late Rect menuRect;
 
     Future<void> popUpAndDown(Widget frame) async {
       await tester.pumpWidget(frame);
@@ -1197,7 +1195,7 @@ void main() {
       buttonKey: key,
       value: null,
       items: menuItems,
-      onChanged: (String _) { },
+      onChanged: (String? _) { },
       hint: const Text('test'),
     ));
 
@@ -1309,7 +1307,7 @@ void main() {
   testWidgets('disabledHint displays on empty items or onChanged', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
 
-    Widget build({ List<String> items, ValueChanged<String> onChanged }) => buildFrame(
+    Widget build({ List<String>? items, ValueChanged<String?>? onChanged }) => buildFrame(
       items: items,
       onChanged: onChanged,
       buttonKey: buttonKey,
@@ -1349,7 +1347,7 @@ void main() {
     (WidgetTester tester) async {
       final Key buttonKey = UniqueKey();
 
-      Widget build({ List<String> items }){
+      Widget build({ List<String>? items }){
         return buildFrame(
           items: items,
           buttonKey: buttonKey,
@@ -1371,7 +1369,7 @@ void main() {
   testWidgets('DropdownButton disabledHint is null by default', (WidgetTester tester) async {
     final Key buttonKey = UniqueKey();
 
-    Widget build({ List<String> items }){
+    Widget build({ List<String>? items }){
       return buildFrame(
         items: items,
         buttonKey: buttonKey,
@@ -1408,7 +1406,7 @@ void main() {
           );
         }).toList();
       },
-      onChanged: (String newValue) {},
+      onChanged: (String? newValue) {},
     ));
 
     final RenderBox dropdownButtonRenderBox = tester.renderObject<RenderBox>(
@@ -1445,7 +1443,7 @@ void main() {
             );
           }).toList();
         },
-        onChanged: (String newValue) {},
+        onChanged: (String? newValue) {},
       ));
 
       final RenderBox dropdownButtonRenderBox = tester.renderObject<RenderBox>(
@@ -1487,7 +1485,7 @@ void main() {
             );
           }).toList();
         },
-        onChanged: (String newValue) {},
+        onChanged: (String? newValue) {},
       ));
 
       final RenderBox dropdownButtonRenderBox = tester.renderObject<RenderBox>(
@@ -1659,14 +1657,14 @@ void main() {
 
     final DropdownButton<int> button = DropdownButton<int>(
       value: 50,
-      onChanged: (int newValue) { },
+      onChanged: (int? newValue) { },
       items: items,
     );
 
     double getMenuScroll() {
       double scrollPosition;
       final ListView listView = tester.element(find.byType(ListView)).widget as ListView;
-      final ScrollController scrollController = listView.controller;
+      final ScrollController scrollController = listView.controller!;
       assert(scrollController != null);
       scrollPosition = scrollController.position.pixels;
       assert(scrollPosition != null);
@@ -1696,14 +1694,14 @@ void main() {
 
     final DropdownButton<int> button = DropdownButton<int>(
       value: 99,
-      onChanged: (int newValue) { },
+      onChanged: (int? newValue) { },
       items: items,
     );
 
     double getMenuScroll() {
       double scrollPosition;
       final ListView listView = tester.element(find.byType(ListView)).widget as ListView;
-      final ScrollController scrollController = listView.controller;
+      final ScrollController scrollController = listView.controller!;
       assert(scrollController != null);
       scrollPosition = scrollController.position.pixels;
       assert(scrollPosition != null);
@@ -1733,14 +1731,14 @@ void main() {
 
     final DropdownButton<int> button = DropdownButton<int>(
       value: 0,
-      onChanged: (int newValue) { },
+      onChanged: (int? newValue) { },
       items: items,
     );
 
     double getMenuScroll() {
       double scrollPosition;
       final ListView listView = tester.element(find.byType(ListView)).widget as ListView;
-      final ScrollController scrollController = listView.controller;
+      final ScrollController scrollController = listView.controller!;
       assert(scrollController != null);
       scrollPosition = scrollController.position.pixels;
       assert(scrollPosition != null);
@@ -1770,14 +1768,14 @@ void main() {
 
     final DropdownButton<int> button = DropdownButton<int>(
       value: 99,
-      onChanged: (int newValue) { },
+      onChanged: (int? newValue) { },
       items: items,
     );
 
     double getMenuScroll() {
       double scrollPosition;
       final ListView listView = tester.element(find.byType(ListView)).widget as ListView;
-      final ScrollController scrollController = listView.controller;
+      final ScrollController scrollController = listView.controller!;
       assert(scrollController != null);
       scrollPosition = scrollController.position.pixels;
       assert(scrollPosition != null);
@@ -1802,8 +1800,7 @@ void main() {
 
   testWidgets('Dropdown menu respects parent size limits', (WidgetTester tester) async {
     // Regression test for https://github.com/flutter/flutter/issues/24417
-
-    int selectedIndex;
+    int? selectedIndex;
     await tester.pumpWidget(
       MaterialApp(
         home: Scaffold(
@@ -1821,7 +1818,9 @@ void main() {
                       padding: const EdgeInsetsDirectional.only(start: 16.0, end: 24.0),
                       child: DropdownButton<int>(
                         value: 12,
-                        onChanged: (int i) { selectedIndex = i; },
+                        onChanged: (int? i) {
+                          selectedIndex = i;
+                        },
                         items: List<DropdownMenuItem<int>>.generate(100, (int i) {
                           return DropdownMenuItem<int>(value: i, child: Text('$i'));
                         }),
@@ -1875,7 +1874,7 @@ void main() {
       'Two',
       'Three',
     ];
-    String selectedItem = items[0];
+    String? selectedItem = items[0];
 
     await tester.pumpWidget(
       StatefulBuilder(
@@ -1884,7 +1883,9 @@ void main() {
             home: Scaffold(
               body: DropdownButton<String>(
                 value: selectedItem,
-                onChanged: (String string) => setState(() => selectedItem = string),
+                onChanged: (String? string) {
+                  setState(() => selectedItem = string);
+                },
                 selectedItemBuilder: (BuildContext context) {
                   int index = 0;
                   return items.map((String string) {
@@ -1928,7 +1929,7 @@ void main() {
   testWidgets('DropdownButton hint displays properly when selectedItemBuilder is defined', (WidgetTester tester) async {
     // Regression test for https://github.com/flutter/flutter/issues/42340
     final List<String> items = <String>['1', '2', '3'];
-    String selectedItem;
+    String? selectedItem;
 
     await tester.pumpWidget(
       StatefulBuilder(
@@ -1938,9 +1939,11 @@ void main() {
               body: DropdownButton<String>(
                 hint: const Text('Please select an item'),
                 value: selectedItem,
-                onChanged: (String string) => setState(() {
+                onChanged: (String? string) {
+                  setState(() {
                     selectedItem = string;
-                }),
+                  });
+                },
                 selectedItemBuilder: (BuildContext context) {
                   return items.map<Widget>((String item) {
                     return Text('You have selected: $item');
@@ -1971,7 +1974,7 @@ void main() {
 
   testWidgets('Variable size and oversized menu items', (WidgetTester tester) async {
     final List<double> itemHeights = <double>[30, 40, 50, 60];
-    double dropdownValue = itemHeights[0];
+    double? dropdownValue = itemHeights[0];
 
     Widget buildFrame() {
       return MaterialApp(
@@ -1980,7 +1983,7 @@ void main() {
             child: StatefulBuilder(
               builder: (BuildContext context, StateSetter setState) {
                 return DropdownButton<double>(
-                  onChanged: (double value) {
+                  onChanged: (double? value) {
                     setState(() { dropdownValue = value; });
                   },
                   value: dropdownValue,
@@ -2075,18 +2078,18 @@ void main() {
       'two',
       'three',
     ];
-    String item = items[0];
-    MediaQueryData mediaQuery;
+    String? item = items[0];
+    late MediaQueryData mediaQuery;
 
     await tester.pumpWidget(
       StatefulBuilder(
         builder: (BuildContext context, StateSetter setState) {
           return MaterialApp(
-            builder: (BuildContext context, Widget child) {
-              mediaQuery ??= MediaQuery.of(context);
+            builder: (BuildContext context, Widget? child) {
+              mediaQuery = MediaQuery.of(context)!;
               return MediaQuery(
                 data: mediaQuery,
-                child: child,
+                child: child!,
               );
             },
             home: Scaffold(
@@ -2096,7 +2099,7 @@ void main() {
                   value: item,
                   child: Text(item),
                 )).toList(),
-                onChanged: (String newItem) {
+                onChanged: (String? newItem) {
                   setState(() {
                     item = newItem;
                     mediaQuery = mediaQuery.copyWith(
@@ -2127,7 +2130,7 @@ void main() {
   testWidgets('DropdownButton hint is selected item', (WidgetTester tester) async {
     const double hintPaddingOffset = 8;
     const List<String> itemValues = <String>['item0', 'item1', 'item2', 'item3'];
-    String selectedItem = 'item0';
+    String? selectedItem = 'item0';
 
     Widget buildFrame() {
       return MaterialApp(
@@ -2163,7 +2166,7 @@ void main() {
                           );
                         },
                       ),
-                      onChanged: (String value) {
+                      onChanged: (String? value) {
                         setState(() { selectedItem = value; });
                       },
                       icon: Container(),
@@ -2232,7 +2235,7 @@ void main() {
 
   testWidgets('DropdownButton is activated with the enter/space key', (WidgetTester tester) async {
     final FocusNode focusNode = FocusNode(debugLabel: 'DropdownButton');
-    String value = 'one';
+    String? value = 'one';
 
     Widget buildFrame() {
       return MaterialApp(
@@ -2243,7 +2246,7 @@ void main() {
                 return DropdownButton<String>(
                   focusNode: focusNode,
                   autofocus: true,
-                  onChanged: (String newValue) {
+                  onChanged: (String? newValue) {
                     setState(() {
                       value = newValue;
                     });
@@ -2288,7 +2291,7 @@ void main() {
 
   testWidgets('Selected element is focused when dropdown is opened', (WidgetTester tester) async {
     final FocusNode focusNode = FocusNode(debugLabel: 'DropdownButton');
-    String value = 'one';
+    String? value = 'one';
     await tester.pumpWidget(MaterialApp(
       home: Scaffold(
         body: Center(
@@ -2297,7 +2300,7 @@ void main() {
               return DropdownButton<String>(
                 focusNode: focusNode,
                 autofocus: true,
-                onChanged: (String newValue) {
+                onChanged: (String? newValue) {
                   setState(() {
                     value = newValue;
                   });
@@ -2325,7 +2328,7 @@ void main() {
     await tester.pump();
     await tester.pump(const Duration(seconds: 1)); // finish the menu open animation
     expect(value, equals('one'));
-    expect(Focus.of(tester.element(find.byKey(const ValueKey<String>('one')).last)).hasPrimaryFocus, isTrue);
+    expect(Focus.of(tester.element(find.byKey(const ValueKey<String>('one')).last))!.hasPrimaryFocus, isTrue);
 
     await tester.sendKeyEvent(LogicalKeyboardKey.tab); // Focus 'two'
     await tester.pump();
@@ -2342,13 +2345,13 @@ void main() {
     await tester.pump(const Duration(seconds: 1)); // finish the menu open animation
     expect(value, equals('two'));
     final Element element = tester.element(find.byKey(const ValueKey<String>('two')).last);
-    final FocusNode node = Focus.of(element);
+    final FocusNode node = Focus.of(element)!;
     expect(node.hasFocus, isTrue);
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/55320
 
   testWidgets('Selected element is correctly focused with dropdown that more items than fit on the screen', (WidgetTester tester) async {
     final FocusNode focusNode = FocusNode(debugLabel: 'DropdownButton');
-    int value = 1;
+    int? value = 1;
     final List<int> hugeMenuItems = List<int>.generate(50, (int index) => index);
 
     await tester.pumpWidget(
@@ -2360,7 +2363,7 @@ void main() {
                 return DropdownButton<int>(
                   focusNode: focusNode,
                   autofocus: true,
-                  onChanged: (int newValue) {
+                  onChanged: (int? newValue) {
                     setState(() {
                       value = newValue;
                     });
@@ -2389,7 +2392,7 @@ void main() {
     await tester.pump();
     await tester.pump(const Duration(seconds: 1)); // finish the menu open animation
     expect(value, equals(1));
-    expect(Focus.of(tester.element(find.byKey(const ValueKey<int>(1)).last)).hasPrimaryFocus, isTrue);
+    expect(Focus.of(tester.element(find.byKey(const ValueKey<int>(1)).last))!.hasPrimaryFocus, isTrue);
 
     for (int i = 0; i < 41; ++i) {
       await tester.sendKeyEvent(LogicalKeyboardKey.tab); // Move to the next one.
@@ -2405,13 +2408,13 @@ void main() {
     await tester.pump(const Duration(seconds: 1)); // finish the menu open animation
     expect(value, equals(42));
     final Element element = tester.element(find.byKey(const ValueKey<int>(42)).last);
-    final FocusNode node = Focus.of(element);
+    final FocusNode node = Focus.of(element)!;
     expect(node.hasFocus, isTrue);
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/55320
 
   testWidgets("Having a focused element doesn't interrupt scroll when flung by touch", (WidgetTester tester) async {
     final FocusNode focusNode = FocusNode(debugLabel: 'DropdownButton');
-    int value = 1;
+    int? value = 1;
     final List<int> hugeMenuItems = List<int>.generate(100, (int index) => index);
 
     await tester.pumpWidget(
@@ -2423,7 +2426,7 @@ void main() {
                 return DropdownButton<int>(
                   focusNode: focusNode,
                   autofocus: true,
-                  onChanged: (int newValue) {
+                  onChanged: (int? newValue) {
                     setState(() {
                       value = newValue;
                     });
@@ -2451,14 +2454,14 @@ void main() {
     await tester.sendKeyEvent(LogicalKeyboardKey.enter);
     await tester.pumpAndSettle();
     expect(value, equals(1));
-    expect(Focus.of(tester.element(find.byKey(const ValueKey<int>(1)).last)).hasPrimaryFocus, isTrue);
+    expect(Focus.of(tester.element(find.byKey(const ValueKey<int>(1)).last))!.hasPrimaryFocus, isTrue);
 
     // Move to an item very far down the menu.
     for (int i = 0; i < 90; ++i) {
       await tester.sendKeyEvent(LogicalKeyboardKey.tab); // Move to the next one.
       await tester.pumpAndSettle(); // Wait for it to animate the menu.
     }
-    expect(Focus.of(tester.element(find.byKey(const ValueKey<int>(91)).last)).hasPrimaryFocus, isTrue);
+    expect(Focus.of(tester.element(find.byKey(const ValueKey<int>(91)).last))!.hasPrimaryFocus, isTrue);
 
     // Scroll back to the top using touch, and make sure we end up there.
     final Finder menu = find.byWidgetPredicate((Widget widget) {
@@ -2480,14 +2483,14 @@ void main() {
 
     // Scrolling to the top again has removed the one the focus was on from the
     // tree, causing it to lose focus.
-    expect(Focus.of(tester.element(find.byKey(const ValueKey<int>(91)).last)).hasPrimaryFocus, isFalse);
+    expect(Focus.of(tester.element(find.byKey(const ValueKey<int>(91)).last))!.hasPrimaryFocus, isFalse);
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/55320
 
   testWidgets('DropdownButton onTap callback is called when defined', (WidgetTester tester) async {
     int dropdownButtonTapCounter = 0;
-    String value = 'one';
+    String? value = 'one';
 
-    void onChanged(String newValue) { value = newValue; }
+    void onChanged(String? newValue) { value = newValue; }
     void onTap() { dropdownButtonTapCounter += 1; }
 
     Widget build() => buildFrame(
@@ -2529,9 +2532,9 @@ void main() {
   });
 
   testWidgets('DropdownMenuItem onTap callback is called when defined', (WidgetTester tester) async {
-    String value = 'one';
+    String? value = 'one';
     final List<int> menuItemTapCounters = <int>[0, 0, 0, 0];
-    void onChanged(String newValue) { value = newValue; }
+    void onChanged(String? newValue) { value = newValue; }
 
     final List<VoidCallback> onTapCallbacks = <VoidCallback>[
       () { menuItemTapCounters[0] += 1; },

packages/flutter/test/material/elevated_button_test.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/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -44,10 +42,10 @@ void main() {
     expect(material.elevation, 2);
     expect(material.shadowColor, const Color(0xff000000));
     expect(material.shape, RoundedRectangleBorder(borderRadius: BorderRadius.circular(4)));
-    expect(material.textStyle.color, colorScheme.onPrimary);
-    expect(material.textStyle.fontFamily, 'Roboto');
-    expect(material.textStyle.fontSize, 14);
-    expect(material.textStyle.fontWeight, FontWeight.w500);
+    expect(material.textStyle!.color, colorScheme.onPrimary);
+    expect(material.textStyle!.fontFamily, 'Roboto');
+    expect(material.textStyle!.fontSize, 14);
+    expect(material.textStyle!.fontWeight, FontWeight.w500);
     expect(material.type, MaterialType.button);
 
     final Offset center = tester.getCenter(find.byType(ElevatedButton));
@@ -67,10 +65,10 @@ void main() {
     expect(material.elevation, 8);
     expect(material.shadowColor, const Color(0xff000000));
     expect(material.shape, RoundedRectangleBorder(borderRadius: BorderRadius.circular(4)));
-    expect(material.textStyle.color, colorScheme.onPrimary);
-    expect(material.textStyle.fontFamily, 'Roboto');
-    expect(material.textStyle.fontSize, 14);
-    expect(material.textStyle.fontWeight, FontWeight.w500);
+    expect(material.textStyle!.color, colorScheme.onPrimary);
+    expect(material.textStyle!.fontFamily, 'Roboto');
+    expect(material.textStyle!.fontSize, 14);
+    expect(material.textStyle!.fontWeight, FontWeight.w500);
     expect(material.type, MaterialType.button);
 
     await gesture.up();
@@ -101,10 +99,10 @@ void main() {
     expect(material.elevation, 0.0);
     expect(material.shadowColor, const Color(0xff000000));
     expect(material.shape, RoundedRectangleBorder(borderRadius: BorderRadius.circular(4)));
-    expect(material.textStyle.color, colorScheme.onSurface.withOpacity(0.38));
-    expect(material.textStyle.fontFamily, 'Roboto');
-    expect(material.textStyle.fontSize, 14);
-    expect(material.textStyle.fontWeight, FontWeight.w500);
+    expect(material.textStyle!.color, colorScheme.onSurface.withOpacity(0.38));
+    expect(material.textStyle!.fontFamily, 'Roboto');
+    expect(material.textStyle!.fontSize, 14);
+    expect(material.textStyle!.fontWeight, FontWeight.w500);
     expect(material.type, MaterialType.button);
   });
 
@@ -197,7 +195,7 @@ void main() {
     );
 
     Color textColor() {
-      return tester.renderObject<RenderParagraph>(find.text('ElevatedButton')).text.style.color;
+      return tester.renderObject<RenderParagraph>(find.text('ElevatedButton')).text.style!.color!;
     }
 
     // Default, not disabled.
@@ -276,7 +274,7 @@ void main() {
       ),
     );
 
-    Color iconColor() => _iconStyle(tester, Icons.add).color;
+    Color iconColor() => _iconStyle(tester, Icons.add).color!;
     // Default, not disabled.
     expect(iconColor(), equals(defaultColor));
 
@@ -307,7 +305,7 @@ void main() {
     bool wasPressed;
     Finder elevatedButton;
 
-    Widget buildFrame({ VoidCallback onPressed, VoidCallback onLongPress }) {
+    Widget buildFrame({ VoidCallback? onPressed, VoidCallback? onLongPress }) {
       return Directionality(
         textDirection: TextDirection.ltr,
         child: ElevatedButton(
@@ -385,7 +383,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: ElevatedButton(
           style: ButtonStyle(
-            overlayColor: MaterialStateProperty.resolveWith<Color>((Set<MaterialState> states) {
+            overlayColor: MaterialStateProperty.resolveWith<Color?>((Set<MaterialState> states) {
               return states.contains(MaterialState.hovered) ? hoverColor : null;
             }),
           ),
@@ -415,7 +413,7 @@ void main() {
         textDirection: TextDirection.ltr,
         child: ElevatedButton(
           style: ButtonStyle(
-            overlayColor: MaterialStateProperty.resolveWith<Color>((Set<MaterialState> states) {
+            overlayColor: MaterialStateProperty.resolveWith<Color?>((Set<MaterialState> states) {
               return states.contains(MaterialState.focused) ? focusColor : null;
             }),
           ),
@@ -437,7 +435,7 @@ void main() {
   testWidgets('Does ElevatedButton work with autofocus', (WidgetTester tester) async {
     const Color focusColor = Color(0xff001122);
 
-    Color getOverlayColor(Set<MaterialState> states) {
+    Color? getOverlayColor(Set<MaterialState> states) {
       return states.contains(MaterialState.focused) ? focusColor : null;
     }
 
@@ -448,7 +446,7 @@ void main() {
         child: ElevatedButton(
           autofocus: true,
           style: ButtonStyle(
-            overlayColor: MaterialStateProperty.resolveWith<Color>(getOverlayColor),
+            overlayColor: MaterialStateProperty.resolveWith<Color?>(getOverlayColor),
           ),
           focusNode: focusNode,
           onPressed: () { },
@@ -683,7 +681,7 @@ void main() {
 
     const List<double> textScaleFactorOptions = <double>[0.5, 1.0, 1.25, 1.5, 2.0, 2.5, 3.0, 4.0];
     const List<TextDirection> textDirectionOptions = <TextDirection>[TextDirection.ltr, TextDirection.rtl];
-    const List<Widget> iconOptions = <Widget>[null, Icon(Icons.add, size: 18, key: iconKey)];
+    const List<Widget?> iconOptions = <Widget?>[null, Icon(Icons.add, size: 18, key: iconKey)];
 
     // Expected values for each textScaleFactor.
     final Map<double, double> paddingWithoutIconStart = <double, double>{
@@ -743,7 +741,7 @@ void main() {
     }
 
     /// Computes the padding between two [Rect]s, one inside the other.
-    EdgeInsets paddingBetween({ Rect parent, Rect child }) {
+    EdgeInsets paddingBetween({ required Rect parent, required Rect child }) {
       assert (parent.intersect(child) == child);
       return EdgeInsets.fromLTRB(
         child.left - parent.left,
@@ -755,7 +753,7 @@ void main() {
 
     for (final double textScaleFactor in textScaleFactorOptions) {
       for (final TextDirection textDirection in textDirectionOptions) {
-        for (final Widget icon in iconOptions) {
+        for (final Widget? icon in iconOptions) {
           final String testName = 'ElevatedButton'
             ', text scale $textScaleFactor'
             '${icon != null ? ", with icon" : ""}'
@@ -768,7 +766,7 @@ void main() {
                 home: Builder(
                   builder: (BuildContext context) {
                     return MediaQuery(
-                      data: MediaQuery.of(context).copyWith(
+                      data: MediaQuery.of(context)!.copyWith(
                         textScaleFactor: textScaleFactor,
                       ),
                       child: Directionality(
@@ -808,11 +806,11 @@ void main() {
             // Compute expected padding, and check.
 
             final double expectedStart = icon != null
-              ? paddingWithIconStart[textScaleFactor]
-              : paddingWithoutIconStart[textScaleFactor];
+              ? paddingWithIconStart[textScaleFactor]!
+              : paddingWithoutIconStart[textScaleFactor]!;
             final double expectedEnd = icon != null
-              ? paddingWithIconEnd[textScaleFactor]
-              : paddingWithoutIconEnd[textScaleFactor];
+              ? paddingWithIconEnd[textScaleFactor]!
+              : paddingWithoutIconEnd[textScaleFactor]!;
             final EdgeInsets expectedPadding = EdgeInsetsDirectional.fromSTEB(expectedStart, 0, expectedEnd, 0)
               .resolve(textDirection);
 
@@ -823,9 +821,9 @@ void main() {
 
             final RenderBox labelRenderBox = tester.renderObject<RenderBox>(find.byKey(labelKey));
             final Rect labelBounds = globalBounds(labelRenderBox);
-            final RenderBox iconRenderBox = icon == null ? null : tester.renderObject<RenderBox>(find.byKey(iconKey));
-            final Rect iconBounds = icon == null ? null : globalBounds(iconRenderBox);
-            final Rect childBounds = icon == null ? labelBounds : labelBounds.expandToInclude(iconBounds);
+            final RenderBox? iconRenderBox = icon == null ? null : tester.renderObject<RenderBox>(find.byKey(iconKey));
+            final Rect? iconBounds = icon == null ? null : globalBounds(iconRenderBox!);
+            final Rect childBounds = icon == null ? labelBounds : labelBounds.expandToInclude(iconBounds!);
 
             // We measure the `InkResponse` descendant of the button
             // element, because the button has a larger `RenderBox`
@@ -874,8 +872,8 @@ void main() {
             // Check the gap between the icon and the label
             if (icon != null) {
               final double gapWidth = textDirection == TextDirection.ltr
-                ? labelBounds.left - iconBounds.right
-                : iconBounds.left - labelBounds.right;
+                ? labelBounds.left - iconBounds!.right
+                : iconBounds!.left - labelBounds.right;
               expect(gapWidth, paddingWithIconGap[textScaleFactor]);
             }
 
@@ -904,7 +902,7 @@ void main() {
         home: Builder(
           builder: (BuildContext context) {
             return MediaQuery(
-              data: MediaQuery.of(context).copyWith(
+              data: MediaQuery.of(context)!.copyWith(
                 textScaleFactor: 2,
               ),
               child: Scaffold(
@@ -938,7 +936,7 @@ void main() {
     final Color backgroundColor = colorScheme.primary;
     final Color disabledBackgroundColor = colorScheme.onSurface.withOpacity(0.12);
 
-    Widget buildFrame({ bool enabled }) {
+    Widget buildFrame({ required bool enabled }) {
       return MaterialApp(
         theme: ThemeData.from(colorScheme: colorScheme),
         home: Center(
@@ -983,5 +981,5 @@ TextStyle _iconStyle(WidgetTester tester, IconData icon) {
   final RichText iconRichText = tester.widget<RichText>(
     find.descendant(of: find.byIcon(icon), matching: find.byType(RichText)),
   );
-  return iconRichText.text.style;
+  return iconRichText.text.style!;
 }

packages/flutter/test/material/elevated_button_theme_test.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/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -37,10 +35,10 @@ void main() {
     expect(material.elevation, 2);
     expect(material.shadowColor, const Color(0xff000000));
     expect(material.shape, RoundedRectangleBorder(borderRadius: BorderRadius.circular(4.0)));
-    expect(material.textStyle.color, colorScheme.onPrimary);
-    expect(material.textStyle.fontFamily, 'Roboto');
-    expect(material.textStyle.fontSize, 14);
-    expect(material.textStyle.fontWeight, FontWeight.w500);
+    expect(material.textStyle!.color, colorScheme.onPrimary);
+    expect(material.textStyle!.fontFamily, 'Roboto');
+    expect(material.textStyle!.fontSize, 14);
+    expect(material.textStyle!.fontWeight, FontWeight.w500);
   });
 
   group('[Theme, TextTheme, ElevatedButton style overrides]', () {
@@ -78,7 +76,7 @@ void main() {
       enableFeedback: enableFeedback,
     );
 
-    Widget buildFrame({ ButtonStyle buttonStyle, ButtonStyle themeStyle, ButtonStyle overallStyle }) {
+    Widget buildFrame({ ButtonStyle? buttonStyle, ButtonStyle? themeStyle, ButtonStyle? overallStyle }) {
       final Widget child = Builder(
         builder: (BuildContext context) {
           return ElevatedButton(
@@ -124,16 +122,16 @@ void main() {
     void checkButton(WidgetTester tester) {
       final Material material = tester.widget<Material>(findMaterial);
       final InkWell inkWell = tester.widget<InkWell>(findInkWell);
-      expect(material.textStyle.color, onPrimaryColor);
-      expect(material.textStyle.fontSize, 12);
+      expect(material.textStyle!.color, onPrimaryColor);
+      expect(material.textStyle!.fontSize, 12);
       expect(material.color, primaryColor);
       expect(material.shadowColor, shadowColor);
       expect(material.elevation, elevation);
-      expect(MaterialStateProperty.resolveAs<MouseCursor>(inkWell.mouseCursor, enabled), enabledMouseCursor);
-      expect(MaterialStateProperty.resolveAs<MouseCursor>(inkWell.mouseCursor, disabled), disabledMouseCursor);
-      expect(inkWell.overlayColor.resolve(hovered), onPrimaryColor.withOpacity(0.08));
-      expect(inkWell.overlayColor.resolve(focused), onPrimaryColor.withOpacity(0.24));
-      expect(inkWell.overlayColor.resolve(pressed), onPrimaryColor.withOpacity(0.24));
+      expect(MaterialStateProperty.resolveAs<MouseCursor>(inkWell.mouseCursor!, enabled), enabledMouseCursor);
+      expect(MaterialStateProperty.resolveAs<MouseCursor>(inkWell.mouseCursor!, disabled), disabledMouseCursor);
+      expect(inkWell.overlayColor!.resolve(hovered), onPrimaryColor.withOpacity(0.08));
+      expect(inkWell.overlayColor!.resolve(focused), onPrimaryColor.withOpacity(0.24));
+      expect(inkWell.overlayColor!.resolve(pressed), onPrimaryColor.withOpacity(0.24));
       expect(inkWell.enableFeedback, enableFeedback);
       expect(material.borderRadius, null);
       expect(material.shape, shape);
@@ -185,7 +183,7 @@ void main() {
     const Color shadowColor = Color(0xff000001);
     const Color overiddenColor = Color(0xff000002);
 
-    Widget buildFrame({ Color overallShadowColor, Color themeShadowColor, Color shadowColor }) {
+    Widget buildFrame({ Color? overallShadowColor, Color? themeShadowColor, Color? shadowColor }) {
       return MaterialApp(
         theme: ThemeData.from(colorScheme: colorScheme).copyWith(
           shadowColor: overallShadowColor,

packages/flutter/test/material/expand_icon_test.dart

@@ -2,12 +2,10 @@
 // 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/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-Widget wrap({ Widget child, ThemeData theme }) {
+Widget wrap({ required Widget child, ThemeData? theme }) {
   return MaterialApp(
     theme: theme,
     home: Center(

packages/flutter/test/material/expansion_panel_test.dart

@@ -2,14 +2,12 @@
 // 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/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 class SimpleExpansionPanelListTestWidget extends StatefulWidget {
   const SimpleExpansionPanelListTestWidget({
-    Key key,
+    Key? key,
     this.firstPanelKey,
     this.secondPanelKey,
     this.canTapOnHeader = false,
@@ -18,14 +16,14 @@ class SimpleExpansionPanelListTestWidget extends StatefulWidget {
     this.elevation = 2,
   }) : super(key: key);
 
-  final Key firstPanelKey;
-  final Key secondPanelKey;
+  final Key? firstPanelKey;
+  final Key? secondPanelKey;
   final bool canTapOnHeader;
-  final Color dividerColor;
+  final Color? dividerColor;
   final int elevation;
 
   /// If null, the default [ExpansionPanelList]'s expanded header padding value is applied via [defaultExpandedHeaderPadding]
-  final EdgeInsets expandedHeaderPadding;
+  final EdgeInsets? expandedHeaderPadding;
 
   /// Mirrors the default expanded header padding as its source constants are private.
   static EdgeInsets defaultExpandedHeaderPadding()
@@ -74,7 +72,7 @@ class _SimpleExpansionPanelListTestWidgetState extends State<SimpleExpansionPane
 }
 
 class ExpansionPanelListSemanticsTest extends StatefulWidget {
-  const ExpansionPanelListSemanticsTest({ Key key, this.headerKey }) : super(key: key);
+  const ExpansionPanelListSemanticsTest({ Key? key, required this.headerKey }) : super(key: key);
 
   final Key headerKey;
 
@@ -118,8 +116,8 @@ class ExpansionPanelListSemanticsTestState extends State<ExpansionPanelListSeman
 
 void main() {
   testWidgets('ExpansionPanelList test', (WidgetTester tester) async {
-    int index;
-    bool isExpanded;
+    late int index;
+    late bool isExpanded;
 
     await tester.pumpWidget(
       MaterialApp(
@@ -1364,7 +1362,7 @@ void main() {
     final BoxDecoration decoration = decoratedBox.decoration as BoxDecoration;
 
     // For the last DecoratedBox, we will have a Border.top with the provided dividerColor.
-    expect(decoration.border.top.color, dividerColor);
+    expect(decoration.border!.top.color, dividerColor);
   });
 
   testWidgets('ExpansionPanelList.radio respects DividerColor', (WidgetTester tester) async {
@@ -1397,7 +1395,7 @@ void main() {
     final BoxDecoration boxDecoration = decoratedBox.decoration as BoxDecoration;
 
     // For the last DecoratedBox, we will have a Border.top with the provided dividerColor.
-    expect(boxDecoration.border.top.color, dividerColor);
+    expect(boxDecoration.border!.top.color, dividerColor);
   });
 
   testWidgets('elevation is propagated properly to MergeableMaterial', (WidgetTester tester) async {

packages/flutter/test/material/expansion_tile_test.dart

@@ -2,21 +2,19 @@
 // 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_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter/material.dart';
 
 class TestIcon extends StatefulWidget {
-  const TestIcon({Key key}) : super(key: key);
+  const TestIcon({Key? key}) : super(key: key);
 
   @override
   TestIconState createState() => TestIconState();
 }
 
 class TestIconState extends State<TestIcon> {
-  IconThemeData iconTheme;
+  late IconThemeData iconTheme;
 
   @override
   Widget build(BuildContext context) {
@@ -26,7 +24,7 @@ class TestIconState extends State<TestIcon> {
 }
 
 class TestText extends StatefulWidget {
-  const TestText(this.text, {Key key}) : super(key: key);
+  const TestText(this.text, {Key? key}) : super(key: key);
 
   final String text;
 
@@ -35,7 +33,7 @@ class TestText extends StatefulWidget {
 }
 
 class TestTextState extends State<TestText> {
-  TextStyle textStyle;
+  late TextStyle textStyle;
 
   @override
   Widget build(BuildContext context) {
@@ -113,15 +111,15 @@ void main() {
     expect(getHeight(topKey), getHeight(collapsedKey) - 2.0);
     expect(getHeight(topKey), getHeight(defaultKey) - 2.0);
 
-    BoxDecoration expandedContainerDecoration = getContainer(expandedKey).decoration as BoxDecoration;
+    BoxDecoration expandedContainerDecoration = getContainer(expandedKey).decoration! as BoxDecoration;
     expect(expandedContainerDecoration.color, Colors.red);
-    expect(expandedContainerDecoration.border.top.color, _dividerColor);
-    expect(expandedContainerDecoration.border.bottom.color, _dividerColor);
+    expect(expandedContainerDecoration.border!.top.color, _dividerColor);
+    expect(expandedContainerDecoration.border!.bottom.color, _dividerColor);
 
-    BoxDecoration collapsedContainerDecoration = getContainer(collapsedKey).decoration as BoxDecoration;
+    BoxDecoration collapsedContainerDecoration = getContainer(collapsedKey).decoration! as BoxDecoration;
     expect(collapsedContainerDecoration.color, Colors.transparent);
-    expect(collapsedContainerDecoration.border.top.color, Colors.transparent);
-    expect(collapsedContainerDecoration.border.bottom.color, Colors.transparent);
+    expect(collapsedContainerDecoration.border!.top.color, Colors.transparent);
+    expect(collapsedContainerDecoration.border!.bottom.color, Colors.transparent);
 
     await tester.tap(find.text('Expanded'));
     await tester.tap(find.text('Collapsed'));
@@ -131,11 +129,11 @@ void main() {
 
     // Pump to the middle of the animation for expansion.
     await tester.pump(const Duration(milliseconds: 100));
-    final BoxDecoration collapsingContainerDecoration = getContainer(collapsedKey).decoration as BoxDecoration;
+    final BoxDecoration collapsingContainerDecoration = getContainer(collapsedKey).decoration! as BoxDecoration;
     expect(collapsingContainerDecoration.color, Colors.transparent);
     // Opacity should change but color component should remain the same.
-    expect(collapsingContainerDecoration.border.top.color, const Color(0x15333333));
-    expect(collapsingContainerDecoration.border.bottom.color, const Color(0x15333333));
+    expect(collapsingContainerDecoration.border!.top.color, const Color(0x15333333));
+    expect(collapsingContainerDecoration.border!.bottom.color, const Color(0x15333333));
 
     // Pump all the way to the end now.
     await tester.pump(const Duration(seconds: 1));
@@ -145,16 +143,16 @@ void main() {
     expect(getHeight(topKey), getHeight(defaultKey) - getHeight(tileKey) - 2.0);
 
     // Expanded should be collapsed now.
-    expandedContainerDecoration = getContainer(expandedKey).decoration as BoxDecoration;
+    expandedContainerDecoration = getContainer(expandedKey).decoration! as BoxDecoration;
     expect(expandedContainerDecoration.color, Colors.transparent);
-    expect(expandedContainerDecoration.border.top.color, Colors.transparent);
-    expect(expandedContainerDecoration.border.bottom.color, Colors.transparent);
+    expect(expandedContainerDecoration.border!.top.color, Colors.transparent);
+    expect(expandedContainerDecoration.border!.bottom.color, Colors.transparent);
 
     // Collapsed should be expanded now.
-    collapsedContainerDecoration = getContainer(collapsedKey).decoration as BoxDecoration;
+    collapsedContainerDecoration = getContainer(collapsedKey).decoration! as BoxDecoration;
     expect(collapsedContainerDecoration.color, Colors.transparent);
-    expect(collapsedContainerDecoration.border.top.color, _dividerColor);
-    expect(collapsedContainerDecoration.border.bottom.color, _dividerColor);
+    expect(collapsedContainerDecoration.border!.top.color, _dividerColor);
+    expect(collapsedContainerDecoration.border!.bottom.color, _dividerColor);
   }, variant: const TargetPlatformVariant(<TargetPlatform>{ TargetPlatform.iOS,  TargetPlatform.macOS }));
 
   testWidgets('ListTileTheme', (WidgetTester tester) async {
@@ -195,8 +193,8 @@ void main() {
       ),
     );
 
-    Color iconColor(Key key) => tester.state<TestIconState>(find.byKey(key)).iconTheme.color;
-    Color textColor(Key key) => tester.state<TestTextState>(find.byKey(key)).textStyle.color;
+    Color iconColor(Key key) => tester.state<TestIconState>(find.byKey(key)).iconTheme.color!;
+    Color textColor(Key key) => tester.state<TestTextState>(find.byKey(key)).textStyle.color!;
 
     expect(textColor(expandedTitleKey), _accentColor);
     expect(textColor(collapsedTitleKey), _headerColor);

packages/flutter/test/material/feedback_test.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/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -14,18 +12,18 @@ import 'feedback_tester.dart';
 void main () {
   const Duration kWaitDuration = Duration(seconds: 1);
 
-  FeedbackTester feedback;
+  late FeedbackTester feedback;
 
   setUp(() {
     feedback = FeedbackTester();
   });
 
   tearDown(() {
-    feedback?.dispose();
+    feedback.dispose();
   });
 
   group('Feedback on Android', () {
-    List<Map<String, Object>> semanticEvents;
+    late List<Map<String, Object>> semanticEvents;
 
     setUp(() {
       semanticEvents = <Map<String, Object>>[];
@@ -60,10 +58,10 @@ void main () {
       expect(feedback.clickSoundCount, 1);
       expect(semanticEvents.single, <String, dynamic>{
         'type': 'tap',
-        'nodeId': object.debugSemantics.id,
+        'nodeId': object.debugSemantics!.id,
         'data': <String, dynamic>{},
       });
-      expect(object.debugSemantics.getSemanticsData().hasAction(SemanticsAction.tap), true);
+      expect(object.debugSemantics!.getSemanticsData().hasAction(SemanticsAction.tap), true);
 
       semanticsTester.dispose();
     });
@@ -78,7 +76,7 @@ void main () {
 
       await tester.pumpWidget(TestWidget(
         tapHandler: (BuildContext context) {
-          return Feedback.wrapForTap(callback, context);
+          return Feedback.wrapForTap(callback, context)!;
         },
       ));
       await tester.pumpAndSettle(kWaitDuration);
@@ -95,10 +93,10 @@ void main () {
       expect(callbackCount, 1);
       expect(semanticEvents.single, <String, dynamic>{
         'type': 'tap',
-        'nodeId': object.debugSemantics.id,
+        'nodeId': object.debugSemantics!.id,
         'data': <String, dynamic>{},
       });
-      expect(object.debugSemantics.getSemanticsData().hasAction(SemanticsAction.tap), true);
+      expect(object.debugSemantics!.getSemanticsData().hasAction(SemanticsAction.tap), true);
 
       semanticsTester.dispose();
     });
@@ -123,10 +121,10 @@ void main () {
       expect(feedback.clickSoundCount, 0);
       expect(semanticEvents.single, <String, dynamic>{
         'type': 'longPress',
-        'nodeId': object.debugSemantics.id,
+        'nodeId': object.debugSemantics!.id,
         'data': <String, dynamic>{},
       });
-      expect(object.debugSemantics.getSemanticsData().hasAction(SemanticsAction.longPress), true);
+      expect(object.debugSemantics!.getSemanticsData().hasAction(SemanticsAction.longPress), true);
 
       semanticsTester.dispose();
     });
@@ -140,7 +138,7 @@ void main () {
 
       await tester.pumpWidget(TestWidget(
         longPressHandler: (BuildContext context) {
-          return Feedback.wrapForLongPress(callback, context);
+          return Feedback.wrapForLongPress(callback, context)!;
         },
       ));
       await tester.pumpAndSettle(kWaitDuration);
@@ -157,10 +155,10 @@ void main () {
       expect(callbackCount, 1);
       expect(semanticEvents.single, <String, dynamic>{
         'type': 'longPress',
-        'nodeId': object.debugSemantics.id,
+        'nodeId': object.debugSemantics!.id,
         'data': <String, dynamic>{},
       });
-      expect(object.debugSemantics.getSemanticsData().hasAction(SemanticsAction.longPress), true);
+      expect(object.debugSemantics!.getSemanticsData().hasAction(SemanticsAction.longPress), true);
 
       semanticsTester.dispose();
     });
@@ -204,7 +202,7 @@ void main () {
 
 class TestWidget extends StatelessWidget {
   const TestWidget({
-    Key key,
+    Key? key,
     this.tapHandler = nullHandler,
     this.longPressHandler = nullHandler,
   }) : super(key: key);
@@ -212,7 +210,7 @@ class TestWidget extends StatelessWidget {
   final HandlerCreator tapHandler;
   final HandlerCreator longPressHandler;
 
-  static VoidCallback nullHandler(BuildContext context) => null;
+  static VoidCallback? nullHandler(BuildContext context) => null;
 
   @override
   Widget build(BuildContext context) {
@@ -224,4 +222,4 @@ class TestWidget extends StatelessWidget {
   }
 }
 
-typedef HandlerCreator = VoidCallback Function(BuildContext context);
+typedef HandlerCreator = VoidCallback? Function(BuildContext context);