Adds `onReorderStart` and `onReorderEnd` arguments to `ReorderableList`. (#96049)

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

@@ -64,6 +64,8 @@ class ReorderableListView extends StatefulWidget {
     Key? key,
     required List<Widget> children,
     required this.onReorder,
+    this.onReorderStart,
+    this.onReorderEnd,
     this.itemExtent,
     this.prototypeItem,
     this.proxyDecorator,
@@ -131,6 +133,8 @@ class ReorderableListView extends StatefulWidget {
     required this.itemBuilder,
     required this.itemCount,
     required this.onReorder,
+    this.onReorderStart,
+    this.onReorderEnd,
     this.itemExtent,
     this.prototypeItem,
     this.proxyDecorator,
@@ -168,6 +172,12 @@ class ReorderableListView extends StatefulWidget {
   /// {@macro flutter.widgets.reorderable_list.onReorder}
   final ReorderCallback onReorder;
 
+  /// {@macro flutter.widgets.reorderable_list.onReorderStart}
+  final void Function(int index)? onReorderStart;
+
+  /// {@macro flutter.widgets.reorderable_list.onReorderEnd}
+  final void Function(int index)? onReorderEnd;
+
   /// {@macro flutter.widgets.reorderable_list.proxyDecorator}
   final ReorderItemProxyDecorator? proxyDecorator;
 
@@ -479,6 +489,8 @@ class _ReorderableListViewState extends State<ReorderableListView> {
             prototypeItem: widget.prototypeItem,
             itemCount: widget.itemCount,
             onReorder: widget.onReorder,
+            onReorderStart: widget.onReorderStart,
+            onReorderEnd: widget.onReorderEnd,
             proxyDecorator: widget.proxyDecorator ?? _proxyDecorator,
           ),
         ),

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

@@ -114,6 +114,8 @@ class ReorderableList extends StatefulWidget {
     required this.itemBuilder,
     required this.itemCount,
     required this.onReorder,
+    this.onReorderStart,
+    this.onReorderEnd,
     this.itemExtent,
     this.prototypeItem,
     this.proxyDecorator,
@@ -166,6 +168,34 @@ class ReorderableList extends StatefulWidget {
   /// {@endtemplate}
   final ReorderCallback onReorder;
 
+  /// {@template flutter.widgets.reorderable_list.onReorderStart}
+  /// A callback that is called when an item drag has started.
+  ///
+  /// The index parameter of the callback is the index of the selected item.
+  ///
+  /// See also:
+  ///
+  ///   * [onReorderEnd], which is a called when the dragged item is dropped.
+  ///   * [onReorder], which reports that a list item has been dragged to a new
+  ///     location.
+  /// {@endtemplate}
+  final void Function(int index)? onReorderStart;
+
+  /// {@template flutter.widgets.reorderable_list.onReorderEnd}
+  /// A callback that is called when the dragged item is dropped.
+  ///
+  /// The index parameter of the callback is the index where the item is
+  /// dropped. Unlike [onReorder], this is called even when the list item is
+  /// dropped in the same location.
+  ///
+  /// See also:
+  ///
+  ///   * [onReorderStart], which is a called when an item drag has started.
+  ///   * [onReorder], which reports that a list item has been dragged to a new
+  ///     location.
+  /// {@endtemplate}
+  final void Function(int index)? onReorderEnd;
+
   /// {@template flutter.widgets.reorderable_list.proxyDecorator}
   /// A callback that allows the app to add an animated decoration around
   /// an item when it is being dragged.
@@ -360,6 +390,8 @@ class ReorderableListState extends State<ReorderableList> {
             itemBuilder: widget.itemBuilder,
             itemCount: widget.itemCount,
             onReorder: widget.onReorder,
+            onReorderStart: widget.onReorderStart,
+            onReorderEnd: widget.onReorderEnd,
             proxyDecorator: widget.proxyDecorator,
           ),
         ),
@@ -400,6 +432,8 @@ class SliverReorderableList extends StatefulWidget {
     required this.itemBuilder,
     required this.itemCount,
     required this.onReorder,
+    this.onReorderStart,
+    this.onReorderEnd,
     this.itemExtent,
     this.prototypeItem,
     this.proxyDecorator,
@@ -419,6 +453,12 @@ class SliverReorderableList extends StatefulWidget {
   /// {@macro flutter.widgets.reorderable_list.onReorder}
   final ReorderCallback onReorder;
 
+  /// {@macro flutter.widgets.reorderable_list.onReorderStart}
+  final void Function(int)? onReorderStart;
+
+  /// {@macro flutter.widgets.reorderable_list.onReorderEnd}
+  final void Function(int)? onReorderEnd;
+
   /// {@macro flutter.widgets.reorderable_list.proxyDecorator}
   final ReorderItemProxyDecorator? proxyDecorator;
 
@@ -640,6 +680,7 @@ class SliverReorderableListState extends State<SliverReorderableList> with Ticke
     assert(_dragInfo == null);
     final _ReorderableItemState item = _items[_dragIndex!]!;
     item.dragging = true;
+    widget.onReorderStart?.call(_dragIndex!);
     item.rebuild();
     _dragStartTransitionComplete = false;
     SchedulerBinding.instance.addPostFrameCallback((Duration duration) {
@@ -702,6 +743,7 @@ class SliverReorderableListState extends State<SliverReorderableList> with Ticke
         }
       }
     });
+    widget.onReorderEnd?.call(_insertIndex!);
   }
 
   void _dropCompleted() {

packages/flutter/test/material/reorderable_list_test.dart

@@ -1470,6 +1470,82 @@ void main() {
     expect(items.take(8), orderedEquals(<int>[0, 1, 2, 3, 4, 5, 6, 7]));
   });
 
+  testWidgets('ReorderableListView calls onReorderStart and onReorderEnd correctly', (WidgetTester tester) async {
+    final List<int> items = List<int>.generate(8, (int index) => index);
+    int? startIndex, endIndex;
+    final Finder item0 = find.textContaining('item 0');
+
+    void handleReorder(int fromIndex, int toIndex) {
+      if (toIndex > fromIndex) {
+        toIndex -= 1;
+      }
+      items.insert(toIndex, items.removeAt(fromIndex));
+    }
+
+    await tester.pumpWidget(MaterialApp(
+      home: ReorderableListView.builder(
+        itemBuilder: (BuildContext context, int index) {
+          return SizedBox(
+            key: ValueKey<int>(items[index]),
+            height: 100,
+            child: ReorderableDragStartListener(
+              index: index,
+              child: Row(
+                crossAxisAlignment: CrossAxisAlignment.start,
+                children: <Widget>[
+                  Text('item ${items[index]}'),
+                ],
+              ),
+            ),
+          );
+        },
+        itemCount: items.length,
+        onReorder: handleReorder,
+        onReorderStart: (int index) {
+          startIndex = index;
+        },
+        onReorderEnd: (int index) {
+          endIndex = index;
+        },
+      ),
+    ));
+
+    TestGesture drag = await tester.startGesture(tester.getCenter(item0));
+    await tester.pump(kPressTimeout);
+    // Drag enough for move to start.
+    await drag.moveBy(const Offset(0, 20));
+
+    expect(startIndex, equals(0));
+    expect(endIndex, isNull);
+
+    // Move item0 from index 0 to index 3
+    await drag.moveBy(const Offset(0, 300));
+    await tester.pumpAndSettle();
+    await drag.up();
+    await tester.pumpAndSettle();
+
+    expect(endIndex, equals(3));
+
+    startIndex = null;
+    endIndex = null;
+
+    drag = await tester.startGesture(tester.getCenter(item0));
+    await tester.pump(kPressTimeout);
+    // Drag enough for move to start.
+    await drag.moveBy(const Offset(0, 20));
+
+    expect(startIndex, equals(2));
+    expect(endIndex, isNull);
+
+    // Move item0 from index 2 to index 0
+    await drag.moveBy(const Offset(0, -200));
+    await tester.pumpAndSettle();
+    await drag.up();
+    await tester.pumpAndSettle();
+
+    expect(endIndex, equals(0));
+  });
+
   testWidgets('ReorderableListView throws an error when key is not passed to its children', (WidgetTester tester) async {
     final Widget reorderableListView = ReorderableListView.builder(
       itemBuilder: (BuildContext context, int index) {

packages/flutter/test/widgets/reorderable_list_test.dart

@@ -467,6 +467,130 @@ void main() {
     expect(tester.getTopLeft(find.text('item 0')), const Offset(0, 500));
   });
 
+  testWidgets('SliverReorderableList calls onReorderStart and onReorderEnd correctly', (WidgetTester tester) async {
+    final List<int> items = List<int>.generate(8, (int index) => index);
+    int? startIndex, endIndex;
+    final Finder item0 = find.textContaining('item 0');
+
+    await tester.pumpWidget(TestList(
+      items: items,
+      onReorderStart: (int index) {
+        startIndex = index;
+      },
+      onReorderEnd: (int index) {
+        endIndex = index;
+      },
+    ));
+
+    TestGesture drag = await tester.startGesture(tester.getCenter(item0));
+    await tester.pump(kPressTimeout);
+    // Drag enough for move to start.
+    await drag.moveBy(const Offset(0, 20));
+
+    expect(startIndex, equals(0));
+    expect(endIndex, isNull);
+
+    // Move item0 from index 0 to index 3
+    await drag.moveBy(const Offset(0, 300));
+    await tester.pumpAndSettle();
+    await drag.up();
+    await tester.pumpAndSettle();
+
+    expect(endIndex, equals(3));
+
+    startIndex = null;
+    endIndex = null;
+
+    drag = await tester.startGesture(tester.getCenter(item0));
+    await tester.pump(kPressTimeout);
+    // Drag enough for move to start.
+    await drag.moveBy(const Offset(0, 20));
+
+    expect(startIndex, equals(2));
+    expect(endIndex, isNull);
+
+    // Move item0 from index 2 to index 0
+    await drag.moveBy(const Offset(0, -200));
+    await tester.pumpAndSettle();
+    await drag.up();
+    await tester.pumpAndSettle();
+
+    expect(endIndex, equals(0));
+  });
+
+  testWidgets('ReorderableList calls onReorderStart and onReorderEnd correctly', (WidgetTester tester) async {
+    final List<int> items = List<int>.generate(8, (int index) => index);
+    int? startIndex, endIndex;
+    final Finder item0 = find.textContaining('item 0');
+
+    void handleReorder(int fromIndex, int toIndex) {
+      if (toIndex > fromIndex) {
+        toIndex -= 1;
+      }
+      items.insert(toIndex, items.removeAt(fromIndex));
+    }
+
+    await tester.pumpWidget(MaterialApp(
+      home: ReorderableList(
+        itemCount: items.length,
+        itemBuilder: (BuildContext context, int index) {
+          return SizedBox(
+            key: ValueKey<int>(items[index]),
+            height: 100,
+            child: ReorderableDelayedDragStartListener(
+              index: index,
+              child: Text('item ${items[index]}'),
+            ),
+          );
+        },
+        onReorder: handleReorder,
+        onReorderStart: (int index) {
+          startIndex = index;
+        },
+        onReorderEnd: (int index) {
+          endIndex = index;
+        },
+      ),
+    ));
+
+    TestGesture drag = await tester.startGesture(tester.getCenter(item0));
+    await tester.pump(kLongPressTimeout);
+    // Drag enough for move to start.
+    await drag.moveBy(const Offset(0, 20));
+
+    expect(startIndex, equals(0));
+    expect(endIndex, isNull);
+
+    // Move item0 from index 0 to index 3
+    await drag.moveBy(const Offset(0, 300));
+    await tester.pumpAndSettle();
+    await drag.up();
+    await tester.pumpAndSettle();
+
+    expect(endIndex, equals(3));
+
+    startIndex = null;
+    endIndex = null;
+
+    drag = await tester.startGesture(tester.getCenter(item0));
+    await tester.pump(kLongPressTimeout);
+    // Drag enough for move to start.
+    await drag.moveBy(const Offset(0, 20));
+
+    expect(startIndex, equals(2));
+    expect(endIndex, isNull);
+
+    // Move item0 from index 2 to index 0
+    await drag.moveBy(const Offset(0, -200));
+    await tester.pumpAndSettle();
+    await drag.up();
+    await tester.pumpAndSettle();
+
+    expect(endIndex, equals(0));
+  });
+
+
+
   testWidgets('ReorderableList asserts on both non-null itemExtent and prototypeItem', (WidgetTester tester) async {
     final List<int> numbers = <int>[0,1,2];
     expect(() => ReorderableList(
@@ -794,6 +918,8 @@ class TestList extends StatefulWidget {
     this.proxyDecorator,
     required this.items,
     this.reverse = false,
+    this.onReorderStart,
+    this.onReorderEnd,
   }) : super(key: key);
 
   final List<int> items;
@@ -801,6 +927,7 @@ class TestList extends StatefulWidget {
   final Color? iconColor;
   final ReorderItemProxyDecorator? proxyDecorator;
   final bool reverse;
+  final void Function(int)? onReorderStart, onReorderEnd;
 
   @override
   State<TestList> createState() => _TestListState();
@@ -849,6 +976,8 @@ class _TestListState extends State<TestList> {
                         });
                       },
                       proxyDecorator: widget.proxyDecorator,
+                      onReorderStart: widget.onReorderStart,
+                      onReorderEnd: widget.onReorderEnd,
                     ),
                   ],
                 );