Apply indexToItemIndex to indices returned by findChildIndexCallback in SliverAnimatedListState (#108710)

Author: otto-dev

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

@@ -514,7 +514,12 @@ class SliverAnimatedListState extends State<SliverAnimatedList> with TickerProvi
     return SliverChildBuilderDelegate(
       _itemBuilder,
       childCount: _itemsCount,
-      findChildIndexCallback: widget.findChildIndexCallback,
+      findChildIndexCallback: widget.findChildIndexCallback == null
+          ? null
+          : (Key key) {
+              final int? index = widget.findChildIndexCallback!(key);
+              return index != null ? _indexToItemIndex(index) : null;
+            },
     );
   }
 

packages/flutter/test/widgets/animated_list_test.dart

@@ -357,6 +357,67 @@ void main() {
       expect(find.text('removing'), findsNothing);
       expect(tester.getTopLeft(find.text('item 0')).dy, 200);
     });
+
+    testWidgets('passes correctly derived index of findChildIndexCallback to the inner SliverChildBuilderDelegate', (WidgetTester tester) async {
+      final List<int> items = <int>[0, 1, 2, 3];
+      final GlobalKey<SliverAnimatedListState> listKey = GlobalKey<SliverAnimatedListState>();
+
+      await tester.pumpWidget(
+        Directionality(
+          textDirection: TextDirection.ltr,
+          child: CustomScrollView(
+            slivers: <Widget>[
+              SliverAnimatedList(
+                key: listKey,
+                initialItemCount: items.length,
+                itemBuilder: (BuildContext context, int index, Animation<double> animation) {
+                  return _StatefulListItem(
+                    key: ValueKey<int>(items[index]),
+                    index: index,
+                  );
+                },
+                findChildIndexCallback: (Key key) {
+                  final int index = items.indexOf((key as ValueKey<int>).value);
+                  return index == -1 ? null : index;
+                },
+              ),
+            ],
+          ),
+        ),
+      );
+
+      // get all list entries in order
+      final List<Text> listEntries = find.byType(Text).evaluate().map((Element e) => e.widget as Text).toList();
+
+      // check that the list is rendered in the correct order
+      expect(listEntries[0].data, equals('item 0'));
+      expect(listEntries[1].data, equals('item 1'));
+      expect(listEntries[2].data, equals('item 2'));
+      expect(listEntries[3].data, equals('item 3'));
+
+
+      // delete one item
+      listKey.currentState?.removeItem(0, (BuildContext context, Animation<double> animation) {
+        return Container();
+      });
+
+      // delete from list
+      items.removeAt(0);
+
+      // reorder list
+      items.insert(0, items.removeLast());
+
+      // render with new list order
+      await tester.pumpAndSettle();
+
+      // get all list entries in order
+      final List<Text> reorderedListEntries = find.byType(Text).evaluate().map((Element e) => e.widget as Text).toList();
+
+      // check that the stateful items of the list are rendered in the order provided by findChildIndexCallback
+      expect(reorderedListEntries[0].data, equals('item 3'));
+      expect(reorderedListEntries[1].data, equals('item 1'));
+      expect(reorderedListEntries[2].data, equals('item 2'));
+    });
   });
 
   testWidgets(
@@ -428,3 +489,25 @@ void main() {
     expect(tester.widget<CustomScrollView>(find.byType(CustomScrollView)).clipBehavior, clipBehavior);
   });
 }
+
+
+class _StatefulListItem extends StatefulWidget {
+  const _StatefulListItem({
+    super.key,
+    required this.index,
+  });
+
+  final int index;
+
+  @override
+  _StatefulListItemState createState() => _StatefulListItemState();
+}
+
+class _StatefulListItemState extends State<_StatefulListItem> {
+  late final int number = widget.index;
+
+  @override
+  Widget build(BuildContext context) {
+    return Text('item $number');
+  }
+}