Migrated some more widgets doc comments to null safety. (#72838)

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

@@ -90,7 +90,7 @@ typedef AnimatedSwitcherLayoutBuilder = Widget Function(Widget? currentChild, Li
 /// The type of transition can be changed from a cross-fade to a custom
 /// transition by setting the [transitionBuilder].
 ///
-/// {@tool dartpad --template=stateful_widget_material_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_material}
 /// This sample shows a counter that animates the scale of a text widget
 /// whenever the value changes.
 ///

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

@@ -84,7 +84,7 @@ const int _kObscureShowLatestCharCursorTicks = 3;
 ///
 /// Remember to [dispose] of the [TextEditingController] when it is no longer
 /// needed. This will ensure we discard any resources used by the object.
-/// {@tool dartpad --template=stateful_widget_material_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_material}
 /// This example creates a [TextField] with a [TextEditingController] whose
 /// change listener forces the entered text to be lower case and keeps the
 /// cursor at the end of the input.
@@ -926,18 +926,13 @@ class EditableText extends StatefulWidget {
   /// and selection, one can add a listener to its [controller] with
   /// [TextEditingController.addListener].
   ///
-  /// {@tool dartpad --template=stateful_widget_material_no_null_safety}
+  /// {@tool dartpad --template=stateful_widget_material}
   ///
   /// This example shows how onChanged could be used to check the TextField's
   /// current value each time the user inserts or deletes a character.
   ///
   /// ```dart
-  /// TextEditingController _controller;
-  ///
-  /// void initState() {
-  ///   super.initState();
-  ///   _controller = TextEditingController();
-  /// }
+  /// final TextEditingController _controller = TextEditingController();
   ///
   /// void dispose() {
   ///   _controller.dispose();
@@ -961,7 +956,7 @@ class EditableText extends StatefulWidget {
   ///               context: context,
   ///               builder: (BuildContext context) {
   ///                 return AlertDialog(
-  ///                   title: const Text('Thats correct!'),
+  ///                   title: const Text('That is correct!'),
   ///                   content: Text ('13 is the right answer.'),
   ///                   actions: <Widget>[
   ///                     TextButton(

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

@@ -303,10 +303,10 @@ enum UnfocusDisposition {
 /// [DirectionalFocusTraversalPolicyMixin], but custom policies can be built
 /// based upon these policies. See [FocusTraversalPolicy] for more information.
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_no_null_safety} This example shows how
-/// a FocusNode should be managed if not using the [Focus] or [FocusScope]
-/// widgets. See the [Focus] widget for a similar example using [Focus] and
-/// [FocusScope] widgets.
+/// {@tool dartpad --template=stateless_widget_scaffold}
+/// This example shows how a FocusNode should be managed if not using the
+/// [Focus] or [FocusScope] widgets. See the [Focus] widget for a similar
+/// example using [Focus] and [FocusScope] widgets.
 ///
 /// ```dart imports
 /// import 'package:flutter/services.dart';
@@ -314,16 +314,16 @@ enum UnfocusDisposition {
 ///
 /// ```dart preamble
 /// class ColorfulButton extends StatefulWidget {
-///   ColorfulButton({Key key}) : super(key: key);
+///   ColorfulButton({Key? key}) : super(key: key);
 ///
 ///   @override
 ///   _ColorfulButtonState createState() => _ColorfulButtonState();
 /// }
 ///
 /// class _ColorfulButtonState extends State<ColorfulButton> {
-///   FocusNode _node;
+///   late FocusNode _node;
 ///   bool _focused = false;
-///   FocusAttachment _nodeAttachment;
+///   late FocusAttachment _nodeAttachment;
 ///   Color _color = Colors.white;
 ///
 ///   @override
@@ -406,7 +406,7 @@ enum UnfocusDisposition {
 /// Widget build(BuildContext context) {
 ///   final TextTheme textTheme = Theme.of(context).textTheme;
 ///   return DefaultTextStyle(
-///     style: textTheme.headline4,
+///     style: textTheme.headline4!,
 ///     child: ColorfulButton(),
 ///   );
 /// }
@@ -786,7 +786,7 @@ class FocusNode with DiagnosticableTreeMixin, ChangeNotifier {
   /// previous node in the enclosing [FocusTraversalGroup], call [nextFocus] or
   /// [previousFocus] instead of calling `unfocus`.
   ///
-  /// {@tool dartpad --template=stateful_widget_material_no_null_safety}
+  /// {@tool dartpad --template=stateful_widget_material}
   /// This example shows the difference between the different [UnfocusDisposition]
   /// values for [unfocus].
   ///
@@ -835,9 +835,11 @@ class FocusNode with DiagnosticableTreeMixin, ChangeNotifier {
   ///                   children: <Widget>[
   ///                     Radio<UnfocusDisposition>(
   ///                       groupValue: disposition,
-  ///                       onChanged: (UnfocusDisposition value) {
+  ///                       onChanged: (UnfocusDisposition? value) {
   ///                         setState(() {
+  ///                           if (value != null) {
   ///                             disposition = value;
+  ///                           }
   ///                         });
   ///                       },
   ///                       value: UnfocusDisposition.values[index],
@@ -850,7 +852,7 @@ class FocusNode with DiagnosticableTreeMixin, ChangeNotifier {
   ///                 child: const Text('UNFOCUS'),
   ///                 onPressed: () {
   ///                   setState(() {
-  ///                     primaryFocus.unfocus(disposition: disposition);
+  ///                     primaryFocus!.unfocus(disposition: disposition);
   ///                   });
   ///                 },
   ///               ),

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

@@ -1256,14 +1256,18 @@ class _OrderedFocusInfo {
 ///
 /// {@macro flutter.widgets.FocusOrder.comparable}
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_center_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold_center}
 /// This sample shows how to assign a traversal order to a widget. In the
 /// example, the focus order goes from bottom right (the "One" button) to top
 /// left (the "Six" button).
 ///
 /// ```dart preamble
 /// class DemoButton extends StatelessWidget {
-///   const DemoButton({this.name, this.autofocus = false, this.order});
+///   const DemoButton({
+///     required this.name,
+///     this.autofocus = false,
+///     required this.order,
+///   });
 ///
 ///   final String name;
 ///   final bool autofocus;
@@ -1466,7 +1470,7 @@ class FocusTraversalOrder extends InheritedWidget {
 /// To prevent the members of the group from being focused, set the
 /// [descendantsAreFocusable] attribute to false.
 ///
-/// {@tool dartpad --template=stateless_widget_material_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_material}
 /// This sample shows three rows of buttons, each grouped by a
 /// [FocusTraversalGroup], each with different traversal order policies. Use tab
 /// traversal to see the order they are traversed in.  The first row follows a
@@ -1479,10 +1483,10 @@ class FocusTraversalOrder extends InheritedWidget {
 /// /// the type of T.
 /// class OrderedButton<T> extends StatefulWidget {
 ///   const OrderedButton({
-///     this.name,
+///     required this.name,
 ///     this.canRequestFocus = true,
 ///     this.autofocus = false,
-///     this.order,
+///     required this.order,
 ///   });
 ///
 ///   final String name;
@@ -1495,7 +1499,7 @@ class FocusTraversalOrder extends InheritedWidget {
 /// }
 ///
 /// class _OrderedButtonState<T> extends State<OrderedButton<T>> {
-///   FocusNode focusNode;
+///   late FocusNode focusNode;
 ///
 ///   @override
 ///   void initState() {
@@ -1508,12 +1512,12 @@ class FocusTraversalOrder extends InheritedWidget {
 ///
 ///   @override
 ///   void dispose() {
-///     focusNode?.dispose();
+///     focusNode.dispose();
 ///     super.dispose();
 ///   }
 ///
 ///   @override
-///   void didUpdateWidget(OrderedButton oldWidget) {
+///   void didUpdateWidget(OrderedButton<T> oldWidget) {
 ///     super.didUpdateWidget(oldWidget);
 ///     focusNode.canRequestFocus = widget.canRequestFocus;
 ///   }
@@ -1533,7 +1537,7 @@ class FocusTraversalOrder extends InheritedWidget {
 ///       order = LexicalFocusOrder(widget.order.toString());
 ///     }
 ///
-///     Color overlayColor(Set<MaterialState> states) {
+///     Color? overlayColor(Set<MaterialState> states) {
 ///       if (states.contains(MaterialState.focused)) {
 ///         return Colors.red;
 ///       }
@@ -1543,7 +1547,7 @@ class FocusTraversalOrder extends InheritedWidget {
 ///       return null;  // defer to the default overlayColor
 ///     }
 ///
-///     Color foregroundColor(Set<MaterialState> states) {
+///     Color? foregroundColor(Set<MaterialState> states) {
 ///       if (states.contains(MaterialState.focused) || states.contains(MaterialState.hovered)) {
 ///         return Colors.white;
 ///       }
@@ -1558,8 +1562,8 @@ class FocusTraversalOrder extends InheritedWidget {
 ///           focusNode: focusNode,
 ///           autofocus: widget.autofocus,
 ///           style: ButtonStyle(
-///             overlayColor: MaterialStateProperty.resolveWith<Color>(overlayColor),
-///             foregroundColor: MaterialStateProperty.resolveWith<Color>(foregroundColor),
+///             overlayColor: MaterialStateProperty.resolveWith<Color?>(overlayColor),
+///             foregroundColor: MaterialStateProperty.resolveWith<Color?>(foregroundColor),
 ///           ),
 ///           onPressed: () => _handleOnPressed(),
 ///           child: Text(widget.name),

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

@@ -17,7 +17,7 @@ import 'framework.dart';
 /// like the contents of a new route or an overlay, will be able to see the
 /// ancestor inherited themes of the context it was built in.
 ///
-/// {@tool dartpad --template=freeform_no_null_safety}
+/// {@tool dartpad --template=freeform}
 /// This example demonstrates how `InheritedTheme.capture()` can be used
 /// to wrap the contents of a new route with the inherited themes that
 /// are present when the route was built - but are not present when route

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

@@ -243,7 +243,7 @@ mixin RenderConstrainedLayoutBuilder<ConstraintType extends Constraints, ChildTy
 /// in an [Align] widget. If the child might want to be bigger, consider
 /// wrapping it in a [SingleChildScrollView] or [OverflowBox].
 ///
-/// {@tool dartpad --template=stateless_widget_material_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_material}
 ///
 /// This example uses a [LayoutBuilder] to build a different widget depending on the available width. Resize the
 /// DartPad window to see [LayoutBuilder] in action!

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

@@ -250,7 +250,7 @@ class MediaQueryData {
   /// This property is currently only expected to be set to a non-default value
   /// on Android starting with version Q.
   ///
-  /// {@tool dartpad --template=stateful_widget_material_no_null_safety}
+  /// {@tool dartpad --template=stateful_widget_material}
   ///
   /// For apps that might be deployed on Android Q devices with full gesture
   /// navigation enabled, use [systemGestureInsets] with [Padding]