Adaptive alert dialog (flutter#124336)

Fixes flutter#102811. Adds an adaptive constructor to AlertDialog, along with the adaptive function showAdaptiveDialog.

<img width="357" alt="Screenshot 2023-04-06 at 10 40 18 AM" src="https://user-images.githubusercontent.com/58190796/230455412-31100922-cfc5-4252-b8c6-6f076353f29e.png">
<img width="350" alt="Screenshot 2023-04-06 at 10 42 50 AM" src="https://user-images.githubusercontent.com/58190796/230455454-363dd37e-c44e-4aca-b6a0-cfa1d959f606.png">

examples/api/lib/material/dialog/adaptive_alert_dialog.0.dart

@@ -0,0 +1,76 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/cupertino.dart';
+import 'package:flutter/material.dart';
+
+/// Flutter code sample for [AlertDialog].
+
+void main() => runApp(const AdaptiveAlertDialogApp());
+
+class AdaptiveAlertDialogApp extends StatelessWidget {
+  const AdaptiveAlertDialogApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      // Try this: set the platform to TargetPlatform.android and see the difference
+      theme: ThemeData(platform: TargetPlatform.iOS, useMaterial3: true),
+      home: Scaffold(
+        appBar: AppBar(title: const Text('AlertDialog Sample')),
+        body: const Center(
+          child: AdaptiveDialogExample(),
+        ),
+      ),
+    );
+  }
+}
+
+class AdaptiveDialogExample extends StatelessWidget {
+  const AdaptiveDialogExample({super.key});
+
+  Widget adaptiveAction({
+    required BuildContext context,
+    required VoidCallback onPressed,
+    required Widget child
+  }) {
+    final ThemeData theme = Theme.of(context);
+    switch (theme.platform) {
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        return TextButton(onPressed: onPressed, child: child);
+      case TargetPlatform.iOS:
+      case TargetPlatform.macOS:
+        return CupertinoDialogAction(onPressed: onPressed, child: child);
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return TextButton(
+      onPressed: () => showAdaptiveDialog<String>(
+        context: context,
+        builder: (BuildContext context) => AlertDialog.adaptive(
+          title: const Text('AlertDialog Title'),
+          content: const Text('AlertDialog description'),
+          actions: <Widget>[
+            adaptiveAction(
+              context: context,
+              onPressed: () => Navigator.pop(context, 'Cancel'),
+              child: const Text('Cancel'),
+            ),
+            adaptiveAction(
+              context: context,
+              onPressed: () => Navigator.pop(context, 'OK'),
+              child: const Text('OK'),
+            ),
+          ],
+        ),
+      ),
+      child: const Text('Show Dialog'),
+    );
+  }
+}

examples/api/test/material/dialog/adaptive_alert_dialog.0_test.dart

@@ -0,0 +1,30 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/dialog/adaptive_alert_dialog.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Show Adaptive Alert dialog', (WidgetTester tester) async {
+    const String dialogTitle = 'AlertDialog Title';
+    await tester.pumpWidget(
+      const MaterialApp(
+        home: Scaffold(
+          body: example.AdaptiveAlertDialogApp(),
+        ),
+      ),
+    );
+
+    expect(find.text(dialogTitle), findsNothing);
+
+    await tester.tap(find.widgetWithText(TextButton, 'Show Dialog'));
+    await tester.pumpAndSettle();
+    expect(find.text(dialogTitle), findsOneWidget);
+
+    await tester.tap(find.text('OK'));
+    await tester.pumpAndSettle();
+    expect(find.text(dialogTitle), findsNothing);
+  });
+}

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

@@ -4,8 +4,8 @@
 
 import 'dart:ui';
 
+import 'package:flutter/cupertino.dart';
 import 'package:flutter/foundation.dart' show clampDouble;
-import 'package:flutter/widgets.dart';
 
 import 'color_scheme.dart';
 import 'colors.dart';
@@ -395,6 +395,69 @@ class AlertDialog extends StatelessWidget {
     this.scrollable = false,
   });
 
+  /// Creates an adaptive [AlertDialog] based on whether the target platform is
+  /// iOS or macOS, following Material design's
+  /// [Cross-platform guidelines](https://material.io/design/platform-guidance/cross-platform-adaptation.html).
+  ///
+  /// On iOS and macOS, this constructor creates a [CupertinoAlertDialog]. On
+  /// other platforms, this creates a Material design [AlertDialog].
+  ///
+  /// Typically passed as a child of [showAdaptiveDialog], which will display
+  /// the alert differently based on platform.
+  ///
+  /// If a [CupertinoAlertDialog] is created only these parameters are used:
+  /// [title], [content], [actions], [scrollController],
+  /// [actionScrollController], [insetAnimationDuration], and
+  /// [insetAnimationCurve]. If a material [AlertDialog] is created,
+  /// [scrollController], [actionScrollController], [insetAnimationDuration],
+  /// and [insetAnimationCurve] are ignored.
+  ///
+  /// The target platform is based on the current [Theme]: [ThemeData.platform].
+  ///
+  /// {@tool dartpad}
+  /// This demo shows a [TextButton] which when pressed, calls [showAdaptiveDialog].
+  /// When called, this method displays an adaptive dialog above the current
+  /// contents of the app, with different behaviors depending on target platform.
+  ///
+  /// [CupertinoDialogAction] is conditionally used as the child to show more
+  /// platform specific design.
+  ///
+  /// ** See code in examples/api/lib/material/dialog/adaptive_alert_dialog.0.dart **
+  /// {@end-tool}
+  const factory AlertDialog.adaptive({
+    Key? key,
+    Widget? icon,
+    EdgeInsetsGeometry? iconPadding,
+    Color? iconColor,
+    Widget? title,
+    EdgeInsetsGeometry? titlePadding,
+    TextStyle? titleTextStyle,
+    Widget? content,
+    EdgeInsetsGeometry? contentPadding,
+    TextStyle? contentTextStyle,
+    List<Widget>? actions,
+    EdgeInsetsGeometry? actionsPadding,
+    MainAxisAlignment? actionsAlignment,
+    OverflowBarAlignment? actionsOverflowAlignment,
+    VerticalDirection? actionsOverflowDirection,
+    double? actionsOverflowButtonSpacing,
+    EdgeInsetsGeometry? buttonPadding,
+    Color? backgroundColor,
+    double? elevation,
+    Color? shadowColor,
+    Color? surfaceTintColor,
+    String? semanticLabel,
+    EdgeInsets insetPadding,
+    Clip clipBehavior,
+    ShapeBorder? shape,
+    AlignmentGeometry? alignment,
+    bool scrollable,
+    ScrollController? scrollController,
+    ScrollController? actionScrollController,
+    Duration insetAnimationDuration,
+    Curve insetAnimationCurve,
+  }) = _AdaptiveAlertDialog;
+
   /// An optional icon to display at the top of the dialog.
   ///
   /// Typically, an [Icon] widget. Providing an icon centers the [title]'s text.
@@ -638,6 +701,7 @@ class AlertDialog extends StatelessWidget {
   Widget build(BuildContext context) {
     assert(debugCheckHasMaterialLocalizations(context));
     final ThemeData theme = Theme.of(context);
+
     final DialogTheme dialogTheme = DialogTheme.of(context);
     final DialogTheme defaults = theme.useMaterial3 ? _DialogDefaultsM3(context) : _DialogDefaultsM2(context);
 
@@ -823,6 +887,71 @@ class AlertDialog extends StatelessWidget {
   }
 }
 
+class _AdaptiveAlertDialog extends AlertDialog {
+  const _AdaptiveAlertDialog({
+    super.key,
+    super.icon,
+    super.iconPadding,
+    super.iconColor,
+    super.title,
+    super.titlePadding,
+    super.titleTextStyle,
+    super.content,
+    super.contentPadding,
+    super.contentTextStyle,
+    super.actions,
+    super.actionsPadding,
+    super.actionsAlignment,
+    super.actionsOverflowAlignment,
+    super.actionsOverflowDirection,
+    super.actionsOverflowButtonSpacing,
+    super.buttonPadding,
+    super.backgroundColor,
+    super.elevation,
+    super.shadowColor,
+    super.surfaceTintColor,
+    super.semanticLabel,
+    super.insetPadding = _defaultInsetPadding,
+    super.clipBehavior = Clip.none,
+    super.shape,
+    super.alignment,
+    super.scrollable = false,
+    this.scrollController,
+    this.actionScrollController,
+    this.insetAnimationDuration = const Duration(milliseconds: 100),
+    this.insetAnimationCurve = Curves.decelerate,
+  });
+
+  final ScrollController? scrollController;
+  final ScrollController? actionScrollController;
+  final Duration insetAnimationDuration;
+  final Curve insetAnimationCurve;
+
+  @override
+  Widget build(BuildContext context) {
+    final ThemeData theme = Theme.of(context);
+    switch(theme.platform) {
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        break;
+      case TargetPlatform.iOS:
+      case TargetPlatform.macOS:
+        return CupertinoAlertDialog(
+          title: title,
+          content: content,
+          actions: actions ?? <Widget>[],
+          scrollController: scrollController,
+          actionScrollController: actionScrollController,
+          insetAnimationDuration: insetAnimationDuration,
+          insetAnimationCurve: insetAnimationCurve,
+        );
+    }
+    return super.build(context);
+  }
+}
+
 /// An option used in a [SimpleDialog].
 ///
 /// A simple dialog offers the user a choice between several options. This
@@ -1308,6 +1437,58 @@ Future<T?> showDialog<T>({
   ));
 }
 
+/// Displays either a Material or Cupertino dialog depending on platform.
+///
+/// On most platforms this function will act the same as [showDialog], except
+/// for iOS and macOS, in which case it will act the same as
+/// [showCupertinoDialog].
+///
+/// On Cupertino platforms, [barrierColor], [useSafeArea], and
+/// [traversalEdgeBehavior] are ignored.
+Future<T?> showAdaptiveDialog<T>({
+  required BuildContext context,
+  required WidgetBuilder builder,
+  bool? barrierDismissible,
+  Color? barrierColor = Colors.black54,
+  String? barrierLabel,
+  bool useSafeArea = true,
+  bool useRootNavigator = true,
+  RouteSettings? routeSettings,
+  Offset? anchorPoint,
+  TraversalEdgeBehavior? traversalEdgeBehavior,
+}) {
+  final ThemeData theme = Theme.of(context);
+  switch (theme.platform) {
+    case TargetPlatform.android:
+    case TargetPlatform.fuchsia:
+    case TargetPlatform.linux:
+    case TargetPlatform.windows:
+      return showDialog<T>(
+        context: context,
+        builder: builder,
+        barrierDismissible: barrierDismissible ?? true,
+        barrierColor: barrierColor,
+        barrierLabel: barrierLabel,
+        useSafeArea: useSafeArea,
+        useRootNavigator: useRootNavigator,
+        routeSettings: routeSettings,
+        anchorPoint: anchorPoint,
+        traversalEdgeBehavior: traversalEdgeBehavior,
+      );
+    case TargetPlatform.iOS:
+    case TargetPlatform.macOS:
+      return showCupertinoDialog<T>(
+        context: context,
+        builder: builder,
+        barrierDismissible: barrierDismissible ?? false,
+        barrierLabel: barrierLabel,
+        useRootNavigator: useRootNavigator,
+        anchorPoint: anchorPoint,
+        routeSettings: routeSettings,
+      );
+  }
+}
+
 bool _debugIsActive(BuildContext context) {
   if (context is Element && !context.debugIsActive) {
     throw FlutterError.fromParts(<DiagnosticsNode>[