Support for dismissDirection property in SnackBarTheme (#139068)

This PR introduces a new feature that allows users to configure the 'dismissDirection' in SnackBarTheme. This enhancement provides users with the flexibility to set the 'dismissDirection' property in the ThemeData, rather than having to apply it each time when initializing a snack bar. This streamlines the process and makes it more convenient for users to manage and customize the behavior of snack bars within their applications.

Fixes #139012

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

@@ -289,7 +289,7 @@ class SnackBar extends StatefulWidget {
     this.duration = _snackBarDisplayDuration,
     this.animation,
     this.onVisible,
-    this.dismissDirection = DismissDirection.down,
+    this.dismissDirection,
     this.clipBehavior = Clip.hardEdge,
   }) : assert(elevation == null || elevation >= 0.0),
        assert(width == null || margin == null,
@@ -463,8 +463,10 @@ class SnackBar extends StatefulWidget {
 
   /// The direction in which the SnackBar can be dismissed.
   ///
-  /// Defaults to [DismissDirection.down].
-  final DismissDirection dismissDirection;
+  /// If this property is null, then [SnackBarThemeData.dismissDirection] of
+  /// [ThemeData.snackBarTheme] is used. If that is null, then the default is
+  /// [DismissDirection.down].
+  final DismissDirection? dismissDirection;
 
   /// {@macro flutter.material.Material.clipBehavior}
   ///
@@ -737,6 +739,7 @@ class _SnackBarState extends State<SnackBar> {
     final double elevation = widget.elevation ?? snackBarTheme.elevation ?? defaults.elevation!;
     final Color backgroundColor = widget.backgroundColor ?? snackBarTheme.backgroundColor ?? defaults.backgroundColor!;
     final ShapeBorder? shape = widget.shape ?? snackBarTheme.shape ?? (isFloatingSnackBar ? defaults.shape : null);
+    final DismissDirection dismissDirection = widget.dismissDirection ?? snackBarTheme.dismissDirection ?? DismissDirection.down;
 
     snackBar = Material(
       shape: shape,
@@ -783,7 +786,7 @@ class _SnackBarState extends State<SnackBar> {
       },
       child: Dismissible(
         key: const Key('dismissible'),
-        direction: widget.dismissDirection,
+        direction: dismissDirection,
         resizeDuration: null,
         behavior: widget.hitTestBehavior ?? (widget.margin != null ? HitTestBehavior.deferToChild : HitTestBehavior.opaque),
         onDismissed: (DismissDirection direction) {

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

@@ -70,7 +70,8 @@ class SnackBarThemeData with Diagnosticable {
     this.closeIconColor,
     this.actionOverflowThreshold,
     this.actionBackgroundColor,
-    this.disabledActionBackgroundColor
+    this.disabledActionBackgroundColor,
+    this.dismissDirection,
   })  : assert(elevation == null || elevation >= 0.0),
         assert(width == null || identical(behavior, SnackBarBehavior.floating),
           'Width can only be set if behaviour is SnackBarBehavior.floating'),
@@ -158,6 +159,11 @@ class SnackBarThemeData with Diagnosticable {
   /// If null, [SnackBarAction] falls back to [Colors.transparent].
   final Color? disabledActionBackgroundColor;
 
+  /// Overrides the default value for [SnackBar.dismissDirection].
+  ///
+  /// If null, [SnackBar] will default to [DismissDirection.down].
+  final DismissDirection? dismissDirection;
+
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   SnackBarThemeData copyWith({
@@ -175,6 +181,7 @@ class SnackBarThemeData with Diagnosticable {
     double? actionOverflowThreshold,
     Color? actionBackgroundColor,
     Color? disabledActionBackgroundColor,
+    DismissDirection? dismissDirection,
   }) {
     return SnackBarThemeData(
       backgroundColor: backgroundColor ?? this.backgroundColor,
@@ -191,6 +198,7 @@ class SnackBarThemeData with Diagnosticable {
       actionOverflowThreshold: actionOverflowThreshold ?? this.actionOverflowThreshold,
       actionBackgroundColor: actionBackgroundColor ?? this.actionBackgroundColor,
       disabledActionBackgroundColor: disabledActionBackgroundColor ?? this.disabledActionBackgroundColor,
+      dismissDirection: dismissDirection ?? this.dismissDirection,
     );
   }
 
@@ -215,6 +223,7 @@ class SnackBarThemeData with Diagnosticable {
       actionOverflowThreshold: lerpDouble(a?.actionOverflowThreshold, b?.actionOverflowThreshold, t),
       actionBackgroundColor: Color.lerp(a?.actionBackgroundColor, b?.actionBackgroundColor, t),
       disabledActionBackgroundColor: Color.lerp(a?.disabledActionBackgroundColor, b?.disabledActionBackgroundColor, t),
+      dismissDirection: t < 0.5 ? a?.dismissDirection : b?.dismissDirection,
     );
   }
 
@@ -233,7 +242,8 @@ class SnackBarThemeData with Diagnosticable {
         closeIconColor,
         actionOverflowThreshold,
         actionBackgroundColor,
-        disabledActionBackgroundColor
+        disabledActionBackgroundColor,
+        dismissDirection,
       );
 
   @override
@@ -258,7 +268,8 @@ class SnackBarThemeData with Diagnosticable {
         && other.closeIconColor == closeIconColor
         && other.actionOverflowThreshold == actionOverflowThreshold
         && other.actionBackgroundColor == actionBackgroundColor
-        && other.disabledActionBackgroundColor == disabledActionBackgroundColor;
+        && other.disabledActionBackgroundColor == disabledActionBackgroundColor
+        && other.dismissDirection == dismissDirection;
   }
 
   @override
@@ -278,5 +289,6 @@ class SnackBarThemeData with Diagnosticable {
     properties.add(DoubleProperty('actionOverflowThreshold', actionOverflowThreshold, defaultValue: null));
     properties.add(ColorProperty('actionBackgroundColor', actionBackgroundColor, defaultValue: null));
     properties.add(ColorProperty('disabledActionBackgroundColor', disabledActionBackgroundColor, defaultValue: null));
+    properties.add(DiagnosticsProperty<DismissDirection>('dismissDirection', dismissDirection, defaultValue: null));
   }
 }

packages/flutter/test/material/snack_bar_test.dart

@@ -265,6 +265,101 @@ void main() {
     );
   });
 
+  testWidgetsWithLeakTracking('SnackBar dismissDirection can be customised from SnackBarThemeData', (WidgetTester tester) async {
+    const Key tapTarget = Key('tap-target');
+    late double width;
+
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(
+        snackBarTheme: const SnackBarThemeData(
+          dismissDirection: DismissDirection.startToEnd,
+        )
+      ),
+      home: Scaffold(
+        body: Builder(
+          builder: (BuildContext context) {
+            width = MediaQuery.sizeOf(context).width;
+
+            return GestureDetector(
+              key: tapTarget,
+              onTap: () {
+                ScaffoldMessenger.of(context).showSnackBar(const SnackBar(
+                  content: Text('swipe ltr'),
+                  duration: Duration(seconds: 2),
+                ));
+              },
+              behavior: HitTestBehavior.opaque,
+              child: const SizedBox(
+                height: 100.0,
+                width: 100.0,
+              ),
+            );
+          },
+        ),
+      ),
+    ));
+
+    expect(find.text('swipe ltr'), findsNothing);
+    await tester.tap(find.byKey(tapTarget));
+    expect(find.text('swipe ltr'), findsNothing);
+    await tester.pump(); // schedule animation for snack bar
+    expect(find.text('swipe ltr'), findsOneWidget);
+    await tester.pump(); // begin animation
+    expect(find.text('swipe ltr'), findsOneWidget);
+    await tester.pump(const Duration(milliseconds: 750));
+    await tester.drag(find.text('swipe ltr'), Offset(width, 0.0));
+    await tester.pump(); // snack bar dismissed
+    expect(find.text('swipe ltr'), findsNothing);
+  });
+
+  testWidgetsWithLeakTracking('dismissDirection from SnackBar should be preferred over SnackBarThemeData', (WidgetTester tester) async {
+    const Key tapTarget = Key('tap-target');
+    late double width;
+
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(
+          snackBarTheme: const SnackBarThemeData(
+            dismissDirection: DismissDirection.startToEnd,
+          )
+      ),
+      home: Scaffold(
+        body: Builder(
+          builder: (BuildContext context) {
+            width = MediaQuery.sizeOf(context).width;
+
+            return GestureDetector(
+              key: tapTarget,
+              onTap: () {
+                ScaffoldMessenger.of(context).showSnackBar(const SnackBar(
+                  content: Text('swipe rtl'),
+                  duration: Duration(seconds: 2),
+                  dismissDirection: DismissDirection.endToStart,
+                ));
+              },
+              behavior: HitTestBehavior.opaque,
+              child: const SizedBox(
+                height: 100.0,
+                width: 100.0,
+              ),
+            );
+          },
+        ),
+      ),
+    ));
+
+    expect(find.text('swipe rtl'), findsNothing);
+    await tester.tap(find.byKey(tapTarget));
+    expect(find.text('swipe rtl'), findsNothing);
+    await tester.pump(); // schedule animation for snack bar
+    expect(find.text('swipe rtl'), findsOneWidget);
+    await tester.pump(); // begin animation
+    expect(find.text('swipe rtl'), findsOneWidget);
+    await tester.pump(const Duration(milliseconds: 750));
+    await tester.drag(find.text('swipe rtl'), Offset(-width, 0.0));
+    await tester.pump(); // snack bar dismissed
+    expect(find.text('swipe rtl'), findsNothing);
+  });
+
   testWidgetsWithLeakTracking('SnackBar cannot be tapped twice', (WidgetTester tester) async {
     int tapCount = 0;
     await tester.pumpWidget(MaterialApp(

packages/flutter/test/material/snack_bar_theme_test.dart

@@ -74,6 +74,7 @@ void main() {
       showCloseIcon: false,
       closeIconColor: Color(0xFF0000AA),
       actionOverflowThreshold: 0.5,
+      dismissDirection: DismissDirection.down,
     ).debugFillProperties(builder);
 
     final List<String> description = builder.properties
@@ -94,6 +95,7 @@ void main() {
       'showCloseIcon: false',
       'closeIconColor: Color(0xff0000aa)',
       'actionOverflowThreshold: 0.5',
+      'dismissDirection: DismissDirection.down',
     ]);
   });
 
@@ -618,7 +620,8 @@ SnackBarThemeData _createSnackBarTheme({
   ShapeBorder? shape,
   SnackBarBehavior? behavior,
   Color? actionBackgroundColor,
-  Color? disabledActionBackgroundColor
+  Color? disabledActionBackgroundColor,
+  DismissDirection? dismissDirection
 }) {
   return SnackBarThemeData(
     backgroundColor: backgroundColor,
@@ -629,7 +632,8 @@ SnackBarThemeData _createSnackBarTheme({
     shape: shape,
     behavior: behavior,
     actionBackgroundColor: actionBackgroundColor,
-    disabledActionBackgroundColor: disabledActionBackgroundColor
+    disabledActionBackgroundColor: disabledActionBackgroundColor,
+    dismissDirection: dismissDirection
   );
 }