migrate cupertino to nullsafety (#66493)

packages/flutter/lib/cupertino.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
-
 /// Flutter widgets implementing the current iOS design language.
 ///
 /// To use, import `package:flutter/cupertino.dart`.

packages/flutter/lib/src/cupertino/page_scaffold.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';
 
 import 'colors.dart';
@@ -22,11 +20,11 @@ import 'theme.dart';
 class CupertinoPageScaffold extends StatefulWidget {
   /// Creates a layout for pages with a navigation bar at the top.
   const CupertinoPageScaffold({
-    Key key,
+    Key? key,
     this.navigationBar,
     this.backgroundColor,
     this.resizeToAvoidBottomInset = true,
-    @required this.child,
+    required this.child,
   }) : assert(child != null),
        assert(resizeToAvoidBottomInset != null),
        super(key: key);
@@ -48,7 +46,7 @@ class CupertinoPageScaffold extends StatefulWidget {
   /// in many ways, such as querying [MediaQuery.textScaleFactorOf] against
   /// [CupertinoApp]'s [BuildContext].
   // TODO(xster): document its page transition animation when ready
-  final ObstructingPreferredSizeWidget navigationBar;
+  final ObstructingPreferredSizeWidget? navigationBar;
 
   /// Widget to show in the main content area.
   ///
@@ -61,7 +59,7 @@ class CupertinoPageScaffold extends StatefulWidget {
   /// The color of the widget that underlies the entire scaffold.
   ///
   /// By default uses [CupertinoTheme]'s `scaffoldBackgroundColor` when null.
-  final Color backgroundColor;
+  final Color? backgroundColor;
 
   /// Whether the [child] should size itself to avoid the window's bottom inset.
   ///
@@ -95,12 +93,12 @@ class _CupertinoPageScaffoldState extends State<CupertinoPageScaffold> {
   Widget build(BuildContext context) {
     Widget paddedContent = widget.child;
 
-    final MediaQueryData existingMediaQuery = MediaQuery.of(context);
+    final MediaQueryData existingMediaQuery = MediaQuery.of(context)!;
     if (widget.navigationBar != null) {
       // TODO(xster): Use real size after partial layout instead of preferred size.
       // https://github.com/flutter/flutter/issues/12912
       final double topPadding =
-          widget.navigationBar.preferredSize.height + existingMediaQuery.padding.top;
+          widget.navigationBar!.preferredSize.height + existingMediaQuery.padding.top;
 
       // Propagate bottom padding and include viewInsets if appropriate
       final double bottomPadding = widget.resizeToAvoidBottomInset
@@ -113,7 +111,7 @@ class _CupertinoPageScaffoldState extends State<CupertinoPageScaffold> {
           ? existingMediaQuery.viewInsets.copyWith(bottom: 0.0)
           : existingMediaQuery.viewInsets;
 
-      final bool fullObstruction = widget.navigationBar.shouldFullyObstruct(context);
+      final bool fullObstruction = widget.navigationBar!.shouldFullyObstruct(context);
 
       // If navigation bar is opaquely obstructing, directly shift the main content
       // down. If translucent, let main content draw behind navigation bar but hint the
@@ -176,7 +174,7 @@ class _CupertinoPageScaffoldState extends State<CupertinoPageScaffold> {
               right: 0.0,
               child: MediaQuery(
                 data: existingMediaQuery.copyWith(textScaleFactor: 1),
-                child: widget.navigationBar,
+                child: widget.navigationBar!,
               ),
             ),
           // Add a touch handler the size of the status bar on top of all contents

packages/flutter/lib/src/cupertino/tab_scaffold.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/widgets.dart';
 import 'bottom_tab_bar.dart';
@@ -207,9 +205,9 @@ class CupertinoTabScaffold extends StatefulWidget {
   ///
   /// The [tabBar] and [tabBuilder] arguments must not be null.
   CupertinoTabScaffold({
-    Key key,
-    @required this.tabBar,
-    @required this.tabBuilder,
+    Key? key,
+    required this.tabBar,
+    required this.tabBuilder,
     this.controller,
     this.backgroundColor,
     this.resizeToAvoidBottomInset = true,
@@ -258,7 +256,7 @@ class CupertinoTabScaffold extends StatefulWidget {
   /// index value.
   ///
   /// Defaults to null.
-  final CupertinoTabController controller;
+  final CupertinoTabController? controller;
 
   /// An [IndexedWidgetBuilder] that's called when tabs become active.
   ///
@@ -280,7 +278,7 @@ class CupertinoTabScaffold extends StatefulWidget {
   /// The color of the widget that underlies the entire scaffold.
   ///
   /// By default uses [CupertinoTheme]'s `scaffoldBackgroundColor` when null.
-  final Color backgroundColor;
+  final Color? backgroundColor;
 
   /// Whether the body should size itself to avoid the window's bottom inset.
   ///
@@ -296,7 +294,7 @@ class CupertinoTabScaffold extends StatefulWidget {
 }
 
 class _CupertinoTabScaffoldState extends State<CupertinoTabScaffold> {
-  CupertinoTabController _controller;
+  CupertinoTabController? _controller;
 
   @override
   void initState() {
@@ -317,7 +315,7 @@ class _CupertinoTabScaffoldState extends State<CupertinoTabScaffold> {
     if (shouldDisposeOldController) {
       _controller?.dispose();
     } else if (_controller?._isDisposed == false) {
-      _controller.removeListener(_onCurrentIndexChange);
+      _controller!.removeListener(_onCurrentIndexChange);
     }
 
     newController.addListener(_onCurrentIndexChange);
@@ -326,8 +324,8 @@ class _CupertinoTabScaffoldState extends State<CupertinoTabScaffold> {
 
   void _onCurrentIndexChange() {
     assert(
-      _controller.index >= 0 && _controller.index < widget.tabBar.items.length,
-      "The $runtimeType's current index ${_controller.index} is "
+      _controller!.index >= 0 && _controller!.index < widget.tabBar.items.length,
+      "The $runtimeType's current index ${_controller!.index} is "
       'out of bounds for the tab bar with ${widget.tabBar.items.length} tabs'
     );
 
@@ -341,20 +339,20 @@ class _CupertinoTabScaffoldState extends State<CupertinoTabScaffold> {
     super.didUpdateWidget(oldWidget);
     if (widget.controller != oldWidget.controller) {
       _updateTabController(shouldDisposeOldController: oldWidget.controller == null);
-    } else if (_controller.index >= widget.tabBar.items.length) {
+    } else if (_controller!.index >= widget.tabBar.items.length) {
       // If a new [tabBar] with less than (_controller.index + 1) items is provided,
       // clamp the current index.
-      _controller.index = widget.tabBar.items.length - 1;
+      _controller!.index = widget.tabBar.items.length - 1;
     }
   }
 
   @override
   Widget build(BuildContext context) {
-    final MediaQueryData existingMediaQuery = MediaQuery.of(context);
-    MediaQueryData newMediaQuery = MediaQuery.of(context);
+    final MediaQueryData existingMediaQuery = MediaQuery.of(context)!;
+    MediaQueryData newMediaQuery = MediaQuery.of(context)!;
 
     Widget content = _TabSwitchingView(
-      currentTabIndex: _controller.index,
+      currentTabIndex: _controller!.index,
       tabCount: widget.tabBar.items.length,
       tabBuilder: widget.tabBuilder,
     );
@@ -417,12 +415,11 @@ class _CupertinoTabScaffoldState extends State<CupertinoTabScaffold> {
               // our own listener to update the [_controller.currentIndex] on top of a possibly user
               // provided callback.
               child: widget.tabBar.copyWith(
-                currentIndex: _controller.index,
+                currentIndex: _controller!.index,
                 onTap: (int newIndex) {
-                  _controller.index = newIndex;
+                  _controller!.index = newIndex;
                   // Chain the user's original callback.
-                  if (widget.tabBar.onTap != null)
-                    widget.tabBar.onTap(newIndex);
+                  widget.tabBar.onTap?.call(newIndex);
                 },
               ),
             ),
@@ -438,7 +435,7 @@ class _CupertinoTabScaffoldState extends State<CupertinoTabScaffold> {
     if (widget.controller == null) {
       _controller?.dispose();
     } else if (_controller?._isDisposed == false) {
-      _controller.removeListener(_onCurrentIndexChange);
+      _controller!.removeListener(_onCurrentIndexChange);
     }
 
     super.dispose();
@@ -449,9 +446,9 @@ class _CupertinoTabScaffoldState extends State<CupertinoTabScaffold> {
 /// at a time and on stage. Off stage tabs' animations are stopped.
 class _TabSwitchingView extends StatefulWidget {
   const _TabSwitchingView({
-    @required this.currentTabIndex,
-    @required this.tabCount,
-    @required this.tabBuilder,
+    required this.currentTabIndex,
+    required this.tabCount,
+    required this.tabBuilder,
   }) : assert(currentTabIndex != null),
        assert(tabCount != null && tabCount > 0),
        assert(tabBuilder != null);

packages/flutter/lib/src/cupertino/tab_view.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';
 
 import 'app.dart' show CupertinoApp;
@@ -43,7 +41,7 @@ import 'route.dart';
 class CupertinoTabView extends StatefulWidget {
   /// Creates the content area for a tab in a [CupertinoTabScaffold].
   const CupertinoTabView({
-    Key key,
+    Key? key,
     this.builder,
     this.navigatorKey,
     this.defaultTitle,
@@ -68,7 +66,7 @@ class CupertinoTabView extends StatefulWidget {
   ///  * Calling [State.setState] on a descendant [StatefulWidget]'s [State]
   ///  * Modifying an [InheritedWidget] that a descendant registered itself
   ///    as a dependent to.
-  final WidgetBuilder builder;
+  final WidgetBuilder? builder;
 
   /// A key to use when building this widget's [Navigator].
   ///
@@ -81,10 +79,10 @@ class CupertinoTabView extends StatefulWidget {
   /// tab's state in the process; in that case, the [navigatorObservers]
   /// must also be changed, since the previous observers will be attached to the
   /// previous navigator.
-  final GlobalKey<NavigatorState> navigatorKey;
+  final GlobalKey<NavigatorState>? navigatorKey;
 
   /// The title of the default route.
-  final String defaultTitle;
+  final String? defaultTitle;
 
   /// This tab view's routing table.
   ///
@@ -105,12 +103,12 @@ class CupertinoTabView extends StatefulWidget {
   ///
   /// This routing table is not shared with any routing tables of ancestor or
   /// descendant [Navigator]s.
-  final Map<String, WidgetBuilder> routes;
+  final Map<String, WidgetBuilder>? routes;
 
   /// The route generator callback used when the tab view is navigated to a named route.
   ///
   /// This is used if [routes] does not contain the requested route.
-  final RouteFactory onGenerateRoute;
+  final RouteFactory? onGenerateRoute;
 
   /// Called when [onGenerateRoute] also fails to generate a route.
   ///
@@ -120,7 +118,7 @@ class CupertinoTabView extends StatefulWidget {
   ///
   /// The default implementation pushes a route that displays an ugly error
   /// message.
-  final RouteFactory onUnknownRoute;
+  final RouteFactory? onUnknownRoute;
 
   /// The list of observers for the [Navigator] created in this tab view.
   ///
@@ -134,8 +132,8 @@ class CupertinoTabView extends StatefulWidget {
 }
 
 class _CupertinoTabViewState extends State<CupertinoTabView> {
-  HeroController _heroController;
-  List<NavigatorObserver> _navigatorObservers;
+  late HeroController _heroController;
+  late List<NavigatorObserver> _navigatorObservers;
 
   @override
   void initState() {
@@ -169,15 +167,15 @@ class _CupertinoTabViewState extends State<CupertinoTabView> {
     );
   }
 
-  Route<dynamic> _onGenerateRoute(RouteSettings settings) {
-    final String name = settings.name;
-    WidgetBuilder routeBuilder;
-    String title;
+  Route<dynamic>? _onGenerateRoute(RouteSettings settings) {
+    final String? name = settings.name;
+    WidgetBuilder? routeBuilder;
+    String? title;
     if (name == Navigator.defaultRouteName && widget.builder != null) {
-      routeBuilder = widget.builder;
+      routeBuilder = widget.builder!;
       title = widget.defaultTitle;
     } else if (widget.routes != null) {
-      routeBuilder = widget.routes[name];
+      routeBuilder = widget.routes![name];
     }
     if (routeBuilder != null) {
       return CupertinoPageRoute<dynamic>(
@@ -187,11 +185,11 @@ class _CupertinoTabViewState extends State<CupertinoTabView> {
       );
     }
     if (widget.onGenerateRoute != null)
-      return widget.onGenerateRoute(settings);
+      return widget.onGenerateRoute!(settings);
     return null;
   }
 
-  Route<dynamic> _onUnknownRoute(RouteSettings settings) {
+  Route<dynamic>? _onUnknownRoute(RouteSettings settings) {
     assert(() {
       if (widget.onUnknownRoute == null) {
         throw FlutterError(
@@ -208,7 +206,7 @@ class _CupertinoTabViewState extends State<CupertinoTabView> {
       }
       return true;
     }());
-    final Route<dynamic> result = widget.onUnknownRoute(settings);
+    final Route<dynamic>? result = widget.onUnknownRoute!(settings);
     assert(() {
       if (result == null) {
         throw FlutterError(