Fix gets removedItem instead of its index (#119638)

* fix: gets removedItem instead of its index
add: sliver_animated_list.0_test.dart

* fix: sliver_animated_list.0_test.dart

* fix: pr comments

* fix test import
Co-authored-by: Taha Tesser <tessertaha@gmail.com>

---------
Co-authored-by: Taha Tesser <tessertaha@gmail.com>

examples/api/lib/widgets/animated_list/sliver_animated_list.0.dart

@@ -135,8 +135,8 @@ class _SliverAnimatedListSampleState extends State<SliverAnimatedListSample> {
   }
 }
 
-typedef RemovedItemBuilder = Widget Function(
-    int item, BuildContext context, Animation<double> animation);
+typedef RemovedItemBuilder<E> = Widget Function(
+    E item, BuildContext context, Animation<double> animation);
 
 // Keeps a Dart [List] in sync with an [AnimatedList].
 //
@@ -155,7 +155,7 @@ class ListModel<E> {
   }) : _items = List<E>.from(initialItems ?? <E>[]);
 
   final GlobalKey<SliverAnimatedListState> listKey;
-  final RemovedItemBuilder removedItemBuilder;
+  final RemovedItemBuilder<E> removedItemBuilder;
   final List<E> _items;
 
   SliverAnimatedListState get _animatedList => listKey.currentState!;
@@ -171,7 +171,7 @@ class ListModel<E> {
       _animatedList.removeItem(
         index,
         (BuildContext context, Animation<double> animation) =>
-            removedItemBuilder(index, context, animation),
+            removedItemBuilder(removedItem, context, animation),
       );
     }
     return removedItem;

examples/api/test/widgets/animated_list/sliver_animated_list.0_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/widgets/animated_list/sliver_animated_list.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets(
+    'Items can be selected, added, and removed from SliverAnimatedList',
+    (WidgetTester tester) async {
+      await tester.pumpWidget(const example.SliverAnimatedListSample());
+
+      expect(find.text('Item 0'), findsOneWidget);
+      expect(find.text('Item 1'), findsOneWidget);
+      expect(find.text('Item 2'), findsOneWidget);
+
+      // Add an item at the end of the list
+      await tester.tap(find.byIcon(Icons.add_circle));
+      await tester.pumpAndSettle();
+      expect(find.text('Item 3'), findsOneWidget);
+
+      // Select Item 1.
+      await tester.tap(find.text('Item 1'));
+      await tester.pumpAndSettle();
+
+      // Add item at the top of the list
+      await tester.tap(find.byIcon(Icons.add_circle));
+      await tester.pumpAndSettle();
+      expect(find.text('Item 4'), findsOneWidget);
+
+      // Remove selected item.
+      await tester.tap(find.byIcon(Icons.remove_circle));
+
+      // Item animation is not completed.
+      await tester.pump();
+      expect(find.text('Item 1'), findsOneWidget);
+
+      // When the animation completes, Item 1 disappears.
+      await tester.pumpAndSettle();
+      expect(find.text('Item 1'), findsNothing);
+    },
+  );
+}