[CupertinoAlertDialog] Add tap-slide gesture (#154853)

This PR adds "sliding tap" to `CupertinoAlertDialog` and fixes flutter/flutter#19786. 

Much of the needed infrastructure has been implemented in flutter/flutter#150219, but this time with a new challenge to support disabled buttons, i.e. the button should not show tap highlight when pressed (flutter/flutter#107371).
* Why? Because whether a button is disabled is assigned to `CupertinoDialogAction`, while the background is rendered by a private class that wraps the action widget and built by the dialog body. We need a way to pass the boolean "enabled" from the child to the parent when the action is pressed. After much experimentation, I think the best way is to propagate this boolean using the custom gesture callback.
* An alternative way is to make the wrapper widget use an inherited widget, which allows the child `CupertinoDialogAction` to place a `ValueGetter<bool> getEnabled` to the parent as soon as it's mounted. However, this is pretty ugly...

This PR also fixes flutter/flutter#107371, i.e. disabled `CupertinoDialogAction` no longer triggers the pressing highlight. However, while legacy buttons (custom button classes that are implemented by `GestureDetector.onTap`) still functions (their `onPressed` continues to work), disabled legacy buttons will still show pressing highlight, and there's no plan (actually, no way) to fix it. 

All tests related to sliding taps in `CupertinoActionSheet` has been copied to `CupertinoAlertDialog`, with additional tests for disabled buttons.

Author: dkwingsmt

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

@@ -462,14 +462,16 @@ class _CupertinoAlertDialogState extends State<CupertinoAlertDialog> {
                         width: isInAccessibilityMode
                             ? _kAccessibilityCupertinoDialogWidth
                             : _kCupertinoDialogWidth,
-                        child: CupertinoPopupSurface(
-                          isSurfacePainted: false,
-                          child: Semantics(
-                            namesRoute: true,
-                            scopesRoute: true,
-                            explicitChildNodes: true,
-                            label: localizations.alertDialogLabel,
-                            child: _buildBody(context),
+                        child: _ActionSheetGestureDetector(
+                          child: CupertinoPopupSurface(
+                            isSurfacePainted: false,
+                            child: Semantics(
+                              namesRoute: true,
+                              scopesRoute: true,
+                              explicitChildNodes: true,
+                              label: localizations.alertDialogLabel,
+                              child: _buildBody(context),
+                            ),
                           ),
                         ),
                       ),
@@ -666,10 +668,10 @@ class _SlidingTapGestureRecognizer extends VerticalDragGestureRecognizer {
 // Multiple `_SlideTarget`s might be nested.
 // `_TargetSelectionGestureRecognizer` uses a simple algorithm that only
 // compares if the inner-most slide target has changed (which suffices our use
-// case).  Semantically, this means that all outer targets will be treated as
-// identical to the inner-most one, i.e. when the pointer enters or leaves a
-// slide target, the corresponding method will be called on all targets that
-// nest it.
+// case). Semantically, this means that all outer targets will be treated as
+// having the identical area as the inner-most one, i.e. when the pointer enters
+// or leaves a slide target, the corresponding method will be called on all
+// targets that nest it.
 abstract class _SlideTarget {
   // A pointer has entered this region.
   //
@@ -682,7 +684,10 @@ abstract class _SlideTarget {
   //
   // The `fromPointerDown` should be true if this callback is triggered by a
   // PointerDownEvent, i.e. the second case from the list above.
-  void didEnter({required bool fromPointerDown});
+  //
+  // The return value of this method is used as the `innerEnabled` for the next
+  // target, while `innerEnabled` of the innermost target is true.
+  bool didEnter({required bool fromPointerDown, required bool innerEnabled});
 
   // A pointer has exited this region.
   //
@@ -703,6 +708,10 @@ abstract class _SlideTarget {
 
 // Recognizes sliding taps and thereupon interacts with
 // `_SlideTarget`s.
+//
+// TODO(dkwingsmt): It should recompute hit testing when the app is updated,
+// or better, share code with `MouseTracker`.
+// https://github.com/flutter/flutter/issues/155266
 class _TargetSelectionGestureRecognizer extends GestureRecognizer {
   _TargetSelectionGestureRecognizer({super.debugOwner, required this.hitTest})
     : _slidingTap = _SlidingTapGestureRecognizer(debugOwner: debugOwner) {
@@ -775,8 +784,12 @@ class _TargetSelectionGestureRecognizer extends GestureRecognizer {
       _currentTargets
         ..clear()
         ..addAll(foundTargets);
+      bool enabled = true;
       for (final _SlideTarget target in _currentTargets) {
-        target.didEnter(fromPointerDown: fromPointerDown);
+        enabled = target.didEnter(
+          fromPointerDown: fromPointerDown,
+          innerEnabled: enabled,
+        );
       }
     }
   }
@@ -1234,7 +1247,9 @@ class _CupertinoActionSheetActionState extends State<CupertinoActionSheetAction>
     implements _SlideTarget {
   // |_SlideTarget|
   @override
-  void didEnter({required bool fromPointerDown}) {}
+  bool didEnter({required bool fromPointerDown, required bool innerEnabled}) {
+    return innerEnabled;
+  }
 
   // |_SlideTarget|
   @override
@@ -1377,11 +1392,15 @@ class _ActionSheetButtonBackgroundState extends State<_ActionSheetButtonBackgrou
 
   // |_SlideTarget|
   @override
-  void didEnter({required bool fromPointerDown}) {
+  bool didEnter({required bool fromPointerDown, required bool innerEnabled}) {
+    // Action sheet doesn't support disabled buttons, therefore `innerEnabled`
+    // is always true.
+    assert(innerEnabled);
     widget.onPressStateChange?.call(true);
     if (!fromPointerDown) {
       _emitVibration();
     }
+    return innerEnabled;
   }
 
   // |_SlideTarget|
@@ -1418,7 +1437,7 @@ class _ActionSheetButtonBackgroundState extends State<_ActionSheetButtonBackgrou
           borderRadius: borderRadius,
         ),
         child: widget.child,
-      )
+      ),
     );
   }
 }
@@ -1843,7 +1862,7 @@ class _CupertinoAlertActionSection extends StatelessWidget {
 
 // Renders the background of a button (both the pressed background and the idle
 // background) and reports its state to the parent with `onPressStateChange`.
-class _AlertDialogButtonBackground extends StatelessWidget {
+class _AlertDialogButtonBackground extends StatefulWidget {
   const _AlertDialogButtonBackground({
     required this.idleColor,
     required this.pressedColor,
@@ -1868,37 +1887,58 @@ class _AlertDialogButtonBackground extends StatelessWidget {
   /// Typically a [Text] widget.
   final Widget child;
 
-  void onTapDown(TapDownDetails details) {
-    onPressStateChange?.call(true);
+  @override
+  _AlertDialogButtonBackgroundState createState() => _AlertDialogButtonBackgroundState();
+}
+
+class _AlertDialogButtonBackgroundState extends State<_AlertDialogButtonBackground>
+    implements _SlideTarget {
+  void _emitVibration(){
+    switch (defaultTargetPlatform) {
+      case TargetPlatform.iOS:
+      case TargetPlatform.android:
+        HapticFeedback.selectionClick();
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.macOS:
+      case TargetPlatform.windows:
+        break;
+    }
+  }
+
+  // |_SlideTarget|
+  @override
+  bool didEnter({required bool fromPointerDown, required bool innerEnabled}) {
+    widget.onPressStateChange?.call(innerEnabled);
+    if (innerEnabled && !fromPointerDown) {
+      _emitVibration();
+    }
+    return innerEnabled;
   }
 
-  void onTapUp(TapUpDetails details) {
-    onPressStateChange?.call(false);
+  // |_SlideTarget|
+  @override
+  void didLeave() {
+    widget.onPressStateChange?.call(false);
   }
 
-  void onTapCancel() {
-    onPressStateChange?.call(false);
+  // |_SlideTarget|
+  @override
+  void didConfirm() {
+    widget.onPressStateChange?.call(false);
   }
 
   @override
   Widget build(BuildContext context) {
-    final Color backgroundColor = pressed ? pressedColor : idleColor;
-    return MergeSemantics(
-      // TODO(mattcarroll): Button press dynamics need overhaul for iOS:
-      // https://github.com/flutter/flutter/issues/19786
-      child: GestureDetector(
-        excludeFromSemantics: true,
-        behavior: HitTestBehavior.opaque,
-        onTapDown: onTapDown,
-        onTapUp: onTapUp,
-        // TODO(mattcarroll): Cancel is currently triggered when user moves
-        //  past slop instead of off button: https://github.com/flutter/flutter/issues/19783
-        onTapCancel: onTapCancel,
+    final Color backgroundColor = widget.pressed ? widget.pressedColor : widget.idleColor;
+    return MetaData(
+      metaData: this,
+      child: MergeSemantics(
         child: Container(
           decoration: BoxDecoration(
             color: CupertinoDynamicColor.resolve(backgroundColor, context),
           ),
-          child: child,
+          child: widget.child,
         ),
       ),
     );
@@ -1911,7 +1951,7 @@ class _AlertDialogButtonBackground extends StatelessWidget {
 ///
 ///  * [CupertinoAlertDialog], a dialog that informs the user about situations
 ///    that require acknowledgment.
-class CupertinoDialogAction extends StatelessWidget {
+class CupertinoDialogAction extends StatefulWidget {
   /// Creates an action for an iOS-style dialog.
   const CupertinoDialogAction({
     super.key,
@@ -1958,10 +1998,31 @@ class CupertinoDialogAction extends StatelessWidget {
   /// Typically a [Text] widget.
   final Widget child;
 
-  /// Whether the button is enabled or disabled. Buttons are disabled by
-  /// default. To enable a button, set its [onPressed] property to a non-null
-  /// value.
-  bool get enabled => onPressed != null;
+  @override
+  State<CupertinoDialogAction> createState() => _CupertinoDialogActionState();
+}
+
+class _CupertinoDialogActionState extends State<CupertinoDialogAction>
+    implements _SlideTarget {
+
+  // The button is enabled when it has [onPressed].
+  bool get enabled => widget.onPressed != null;
+
+  // |_SlideTarget|
+  @override
+  bool didEnter({required bool fromPointerDown, required bool innerEnabled}) {
+    return enabled;
+  }
+
+  // |_SlideTarget|
+  @override
+  void didLeave() {}
+
+  // |_SlideTarget|
+  @override
+  void didConfirm() {
+    widget.onPressed?.call();
+  }
 
   // Dialog action content shrinks to fit, up to a certain point, and if it still
   // cannot fit at the minimum size, the text content is ellipsized.
@@ -1991,7 +2052,7 @@ class CupertinoDialogAction extends StatelessWidget {
         ),
         child: Semantics(
           button: true,
-          onTap: onPressed,
+          onTap: widget.onPressed,
           child: DefaultTextStyle(
             style: textStyle,
             textAlign: TextAlign.center,
@@ -2022,12 +2083,12 @@ class CupertinoDialogAction extends StatelessWidget {
   Widget build(BuildContext context) {
     TextStyle style = _kCupertinoDialogActionStyle.copyWith(
       color: CupertinoDynamicColor.resolve(
-        isDestructiveAction ? CupertinoColors.systemRed : CupertinoTheme.of(context).primaryColor,
+        widget.isDestructiveAction ? CupertinoColors.systemRed : CupertinoTheme.of(context).primaryColor,
         context,
       ),
-    ).merge(textStyle);
+    ).merge(widget.textStyle);
 
-    if (isDefaultAction) {
+    if (widget.isDefaultAction) {
       style = style.copyWith(fontWeight: FontWeight.w600);
     }
 
@@ -2047,20 +2108,19 @@ class CupertinoDialogAction extends StatelessWidget {
     final Widget sizedContent = _isInAccessibilityMode(context)
         ? _buildContentWithAccessibilitySizingPolicy(
             textStyle: style,
-            content: child,
+            content: widget.child,
           )
         : _buildContentWithRegularSizingPolicy(
             context: context,
             textStyle: style,
-            content: child,
+            content: widget.child,
             padding: padding,
           );
 
     return MouseRegion(
-      cursor: onPressed != null && kIsWeb ? SystemMouseCursors.click : MouseCursor.defer,
-      child: GestureDetector(
-        excludeFromSemantics: true,
-        onTap: onPressed,
+      cursor: widget.onPressed != null && kIsWeb ? SystemMouseCursors.click : MouseCursor.defer,
+      child: MetaData(
+        metaData: this,
         behavior: HitTestBehavior.opaque,
         child: ConstrainedBox(
           constraints: const BoxConstraints(

packages/flutter/test/cupertino/action_sheet_test.dart

@@ -1035,7 +1035,9 @@ void main() {
     await tester.pumpAndSettle();
 
     // Find the location right within the upper edge of button 1.
-    final Offset start = tester.getTopLeft(find.text('Button 1')) + const Offset(30, -15);
+    final Offset start = tester.getTopLeft(
+      find.widgetWithText(CupertinoActionSheetAction, 'Button 1'),
+    ) + const Offset(30, 5);
     // Verify that the start location is within button 1.
     await tester.tapAt(start);
     expect(pressed, 1);