[NNBD] Migrate sample code pt 1 (#72794)

packages/flutter/lib/src/material/about.dart

@@ -44,14 +44,14 @@ import 'theme.dart';
 /// If your application does not have a [Drawer], you should provide an
 /// affordance to call [showAboutDialog] or (at least) [showLicensePage].
 ///
-/// {@tool dartpad --template=stateless_widget_material_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_material}
 ///
 /// This sample shows two ways to open [AboutDialog]. The first one
 /// uses an [AboutListTile], and the second uses the [showAboutDialog] function.
 ///
 /// ```dart
 ///  Widget build(BuildContext context) {
-///    final TextStyle textStyle = Theme.of(context).textTheme.bodyText2;
+///    final TextStyle textStyle = Theme.of(context).textTheme.bodyText2!;
 ///    final List<Widget> aboutBoxChildren = <Widget>[
 ///      SizedBox(height: 24),
 ///      RichText(

packages/flutter/lib/src/material/card.dart

@@ -20,7 +20,7 @@ import 'theme.dart';
 /// some text describing a musical, and the other with buttons for buying
 /// tickets or listening to the show.](https://flutter.github.io/assets-for-api-docs/assets/material/card.png)
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold}
 ///
 /// This sample shows creation of a [Card] widget that shows album information
 /// and two actions.
@@ -63,7 +63,7 @@ import 'theme.dart';
 /// Sometimes the primary action area of a card is the card itself. Cards can be
 /// one large touch target that shows a detail screen when tapped.
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold}
 ///
 /// This sample shows creation of a [Card] widget that can be tapped. When
 /// tapped this [Card]'s [InkWell] displays an "ink splash" that fills the

packages/flutter/lib/src/material/data_table.dart

@@ -260,7 +260,7 @@ class DataCell {
 /// [PaginatedDataTable] which automatically splits the data into
 /// multiple pages.
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold}
 ///
 /// This sample shows how to display a [DataTable] with three columns: name, age, and
 /// role. The columns are defined by three [DataColumn] objects. The table
@@ -322,7 +322,7 @@ class DataCell {
 /// {@end-tool}
 ///
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold}
 ///
 /// This sample shows how to display a [DataTable] with alternate colors per
 /// row, and a custom color for when the row is selected.
@@ -344,7 +344,7 @@ class DataCell {
 ///       rows: List<DataRow>.generate(
 ///         numItems,
 ///         (index) => DataRow(
-///           color: MaterialStateProperty.resolveWith<Color>((Set<MaterialState> states) {
+///           color: MaterialStateProperty.resolveWith<Color?>((Set<MaterialState> states) {
 ///             // All rows will have the same selected color.
 ///             if (states.contains(MaterialState.selected))
 ///               return Theme.of(context).colorScheme.primary.withOpacity(0.08);
@@ -355,9 +355,9 @@ class DataCell {
 ///           }),
 ///           cells: [DataCell(Text('Row $index'))],
 ///           selected: selected[index],
-///           onSelectChanged: (bool value) {
+///           onSelectChanged: (bool? value) {
 ///             setState(() {
-///               selected[index] = value;
+///               selected[index] = value!;
 ///             });
 ///           },
 ///         ),

packages/flutter/lib/src/material/ink_well.dart

@@ -1171,7 +1171,7 @@ class _InkResponseState extends State<_InkResponseStateWidget>
 ///
 /// An example of this situation is as follows:
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_center_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold_center}
 ///
 /// Tap the container to cause it to grow. Then, tap it again and hold before
 /// the widget reaches its maximum size to observe the clipped ink splash.

packages/flutter/lib/src/material/input_decorator.dart

@@ -2389,7 +2389,7 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
 /// to describe their decoration. (In fact, this class is merely the
 /// configuration of an [InputDecorator], which does all the heavy lifting.)
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold}
 ///
 /// This sample shows how to style a `TextField` using an `InputDecorator`. The
 /// TextField displays a "send message" icon to the left of the input area,
@@ -2414,7 +2414,7 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
 /// ```
 /// {@end-tool}
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold}
 ///
 /// This sample shows how to style a "collapsed" `TextField` using an
 /// `InputDecorator`. The collapsed `TextField` surrounds the hint text and
@@ -2434,7 +2434,7 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
 /// ```
 /// {@end-tool}
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold}
 ///
 /// This sample shows how to create a `TextField` with hint text, a red border
 /// on all sides, and an error message. To display a red border and error
@@ -2455,7 +2455,7 @@ class _InputDecoratorState extends State<InputDecorator> with TickerProviderStat
 /// ```
 /// {@end-tool}
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold}
 ///
 /// This sample shows how to style a `TextField` with a round border and
 /// additional text before and after the input area. It displays "Prefix" before
@@ -2836,7 +2836,8 @@ class InputDecoration {
   /// setting the constraints' minimum height and width to a value lower than
   /// 48px.
   ///
-  /// {@tool dartpad --template=stateless_widget_scaffold_no_null_safety}
+  /// {@tool dartpad --template=stateless_widget_scaffold}
+  ///
   /// This example shows the differences between two `TextField` widgets when
   /// [prefixIconConstraints] is set to the default value and when one is not.
   ///

packages/flutter/lib/src/material/radio_list_tile.dart

@@ -10,7 +10,6 @@ import 'theme.dart';
 import 'theme_data.dart';
 
 // Examples can assume:
-// // @dart = 2.9
 // void setState(VoidCallback fn) { }
 
 /// A [ListTile] with a [Radio]. In other words, a radio button with a label.
@@ -41,7 +40,7 @@ import 'theme_data.dart';
 /// To show the [RadioListTile] as disabled, pass null as the [onChanged]
 /// callback.
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold}
 ///
 /// ![RadioListTile sample](https://flutter.github.io/assets-for-api-docs/assets/material/radio_list_tile.png)
 ///
@@ -52,7 +51,7 @@ import 'theme_data.dart';
 /// enum SingingCharacter { lafayette, jefferson }
 /// ```
 /// ```dart
-/// SingingCharacter _character = SingingCharacter.lafayette;
+/// SingingCharacter? _character = SingingCharacter.lafayette;
 ///
 /// @override
 /// Widget build(BuildContext context) {
@@ -62,13 +61,13 @@ import 'theme_data.dart';
 ///         title: const Text('Lafayette'),
 ///         value: SingingCharacter.lafayette,
 ///         groupValue: _character,
-///         onChanged: (SingingCharacter value) { setState(() { _character = value; }); },
+///         onChanged: (SingingCharacter? value) { setState(() { _character = value; }); },
 ///       ),
 ///       RadioListTile<SingingCharacter>(
 ///         title: const Text('Thomas Jefferson'),
 ///         value: SingingCharacter.jefferson,
 ///         groupValue: _character,
-///         onChanged: (SingingCharacter value) { setState(() { _character = value; }); },
+///         onChanged: (SingingCharacter? value) { setState(() { _character = value; }); },
 ///       ),
 ///     ],
 ///   );
@@ -93,7 +92,7 @@ import 'theme_data.dart';
 /// into one. Therefore, it may be necessary to create a custom radio tile
 /// widget to accommodate similar use cases.
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold}
 ///
 /// ![Radio list tile semantics sample](https://flutter.github.io/assets-for-api-docs/assets/material/radio_list_tile_semantics.png)
 ///
@@ -107,11 +106,11 @@ import 'theme_data.dart';
 /// ```dart preamble
 /// class LinkedLabelRadio extends StatelessWidget {
 ///   const LinkedLabelRadio({
-///     this.label,
-///     this.padding,
-///     this.groupValue,
-///     this.value,
-///     this.onChanged,
+///     required this.label,
+///     required this.padding,
+///     required this.groupValue,
+///     required this.value,
+///     required this.onChanged,
 ///   });
 ///
 ///   final String label;
@@ -129,7 +128,7 @@ import 'theme_data.dart';
 ///           Radio<bool>(
 ///             groupValue: groupValue,
 ///             value: value,
-///             onChanged: (bool newValue) {
+///             onChanged: (bool? newValue) {
 ///               onChanged(newValue);
 ///             }
 ///           ),
@@ -197,7 +196,7 @@ import 'theme_data.dart';
 /// combining [Radio] with other widgets, such as [Text], [Padding] and
 /// [InkWell].
 ///
-/// {@tool dartpad --template=stateful_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateful_widget_scaffold}
 ///
 /// ![Custom radio list tile sample](https://flutter.github.io/assets-for-api-docs/assets/material/radio_list_tile_custom.png)
 ///
@@ -207,11 +206,11 @@ import 'theme_data.dart';
 /// ```dart preamble
 /// class LabeledRadio extends StatelessWidget {
 ///   const LabeledRadio({
-///     this.label,
-///     this.padding,
-///     this.groupValue,
-///     this.value,
-///     this.onChanged,
+///     required this.label,
+///     required this.padding,
+///     required this.groupValue,
+///     required this.value,
+///     required this.onChanged,
 ///   });
 ///
 ///   final String label;
@@ -234,7 +233,7 @@ import 'theme_data.dart';
 ///             Radio<bool>(
 ///               groupValue: groupValue,
 ///               value: value,
-///               onChanged: (bool newValue) {
+///               onChanged: (bool? newValue) {
 ///                 onChanged(newValue);
 ///               },
 ///             ),
@@ -387,12 +386,12 @@ class RadioListTile<T> extends StatelessWidget {
   ///
   /// The default is false.
   ///
-  /// {@tool dartpad --template=stateful_widget_scaffold_no_null_safety}
+  /// {@tool dartpad --template=stateful_widget_scaffold}
   /// This example shows how to enable deselecting a radio button by setting the
   /// [toggleable] attribute.
   ///
   /// ```dart
-  /// int groupValue;
+  /// int? groupValue;
   /// static const List<String> selections = <String>[
   ///   'Hercules Mulligan',
   ///   'Eliza Hamilton',
@@ -411,7 +410,7 @@ class RadioListTile<T> extends StatelessWidget {
   ///           groupValue: groupValue,
   ///           toggleable: true,
   ///           title: Text(selections[index]),
-  ///           onChanged: (int value) {
+  ///           onChanged: (int? value) {
   ///             setState(() {
   ///               groupValue = value;
   ///             });

packages/flutter/lib/src/material/raised_button.dart

@@ -43,7 +43,7 @@ import 'theme_data.dart';
 /// Raised buttons have a minimum size of 88.0 by 36.0 which can be overridden
 /// with [ButtonTheme].
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold}
 ///
 /// This sample shows how to render a disabled RaisedButton, an enabled RaisedButton
 /// and lastly a RaisedButton with gradient background.

packages/flutter/lib/src/material/snack_bar.dart

@@ -158,7 +158,7 @@ class _SnackBarActionState extends State<SnackBarAction> {
 /// A SnackBar with an action will not time out when TalkBack or VoiceOver are
 /// enabled. This is controlled by [AccessibilityFeatures.accessibleNavigation].
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_center_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold_center}
 ///
 /// Here is an example of a [SnackBar] with an [action] button implemented using
 /// [SnackBarAction].
@@ -185,7 +185,7 @@ class _SnackBarActionState extends State<SnackBarAction> {
 /// ```
 /// {@end-tool}
 ///
-/// {@tool dartpad --template=stateless_widget_scaffold_center_no_null_safety}
+/// {@tool dartpad --template=stateless_widget_scaffold_center}
 ///
 /// Here is an example of a customized [SnackBar]. It utilizes
 /// [behavior], [shape], [padding], [width], and [duration] to customize the