Fixes issue, ReorderableListView destroys children even if their key-type wasn't changed (#64855)

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

@@ -363,7 +363,7 @@ class _ReorderableListContentState extends State<_ReorderableListContent> with T
   // Handles up the logic for dragging and reordering items in the list.
   Widget _wrap(Widget toWrap, int index, BoxConstraints constraints) {
     assert(toWrap.key != null);
-    final GlobalObjectKey keyIndexGlobalKey = GlobalObjectKey(toWrap.key);
+    final _ReorderableListViewChildGlobalKey keyIndexGlobalKey = _ReorderableListViewChildGlobalKey(toWrap.key, this);
     // We pass the toWrapWithGlobalKey into the Draggable so that when a list
     // item gets dragged, the accessibility framework can preserve the selected
     // state of the dragging item.
@@ -596,3 +596,30 @@ class _ReorderableListContentState extends State<_ReorderableListContent> with T
     });
   }
 }
+
+// A global key that takes its identity from the object and uses a value of a
+// particular type to identify itself.
+//
+// The difference with GlobalObjectKey is that it uses [==] instead of [identical]
+// of the objects used to generate widgets.
+@optionalTypeArgs
+class _ReorderableListViewChildGlobalKey extends GlobalObjectKey {
+
+  const _ReorderableListViewChildGlobalKey(this.subKey, this.state) : super(subKey);
+
+  final Key subKey;
+
+  final _ReorderableListContentState state;
+
+  @override
+  bool operator ==(Object other) {
+    if (other.runtimeType != runtimeType)
+      return false;
+    return other is _ReorderableListViewChildGlobalKey
+        && other.subKey == subKey
+        && other.state == state;
+  }
+
+  @override
+  int get hashCode => hashValues(subKey, state);
+}

packages/flutter/test/material/reorderable_list_test.dart

@@ -253,6 +253,35 @@ void main() {
         expect(findState(const Key('A')).checked, true);
       });
 
+      testWidgets('Preserves children states when rebuilt', (WidgetTester tester) async {
+        const Key firstBox = Key('key');
+        Widget build() {
+          return MaterialApp(
+            home: Directionality(
+              textDirection: TextDirection.ltr,
+              child: SizedBox(
+                width: 100,
+                height: 100,
+                child: ReorderableListView(
+                  scrollDirection: Axis.vertical,
+                  children: const <Widget>[
+                    SizedBox(key: firstBox, width: 10, height: 10),
+                  ],
+                  onReorder: (_, __) {},
+                ),
+              ),
+            ),
+          );
+        }
+
+        // When the widget is rebuilt, the state of child should be consistent.
+        await tester.pumpWidget(build());
+        final Element e0 = tester.element(find.byKey(firstBox));
+        await tester.pumpWidget(build());
+        final Element e1 = tester.element(find.byKey(firstBox));
+        expect(e0, equals(e1));
+      });
+
       testWidgets('Uses the PrimaryScrollController when available', (WidgetTester tester) async {
         final ScrollController primary = ScrollController();
         final Widget reorderableList = ReorderableListView(
@@ -771,6 +800,35 @@ void main() {
         expect(findState(const Key('A')).checked, true);
       });
 
+      testWidgets('Preserves children states when rebuilt', (WidgetTester tester) async {
+        const Key firstBox = Key('key');
+        Widget build() {
+          return MaterialApp(
+            home: Directionality(
+              textDirection: TextDirection.ltr,
+              child: SizedBox(
+                width: 100,
+                height: 100,
+                child: ReorderableListView(
+                  scrollDirection: Axis.horizontal,
+                  children: const <Widget>[
+                    SizedBox(key: firstBox, width: 10, height: 10),
+                  ],
+                  onReorder: (_, __) {},
+                ),
+              ),
+            ),
+          );
+        }
+
+        // When the widget is rebuilt, the state of child should be consistent.
+        await tester.pumpWidget(build());
+        final Element e0 = tester.element(find.byKey(firstBox));
+        await tester.pumpWidget(build());
+        final Element e1 = tester.element(find.byKey(firstBox));
+        expect(e0, equals(e1));
+      });
+
       group('Accessibility (a11y/Semantics)', () {
         Map<CustomSemanticsAction, VoidCallback> getSemanticsActions(int index) {
           final Semantics semantics = find.ancestor(