| 1 | // Copyright 2014 The Flutter Authors. All rights reserved. |
|---|---|
| 2 | // Use of this source code is governed by a BSD-style license that can be |
| 3 | // found in the LICENSE file. |
| 4 | |
| 5 | import 'package:flutter/material.dart'; |
| 6 | |
| 7 | /// Flutter code sample for a [ListView.custom] using the `findChildIndexCallback` argument. |
| 8 | void main() => runApp(const ListViewExampleApp()); |
| 9 | |
| 10 | class ListViewExampleApp extends StatelessWidget { |
| 11 | const ListViewExampleApp({super.key}); |
| 12 | |
| 13 | @override |
| 14 | Widget build(BuildContext context) { |
| 15 | return const MaterialApp(home: ListViewExample()); |
| 16 | } |
| 17 | } |
| 18 | |
| 19 | class ListViewExample extends StatefulWidget { |
| 20 | const ListViewExample({super.key}); |
| 21 | |
| 22 | @override |
| 23 | State<ListViewExample> createState() => _ListViewExampleState(); |
| 24 | } |
| 25 | |
| 26 | class _ListViewExampleState extends State<ListViewExample> { |
| 27 | List<String> items = <String>['1', '2', '3', '4', '5']; |
| 28 | |
| 29 | void _reverse() { |
| 30 | setState(() { |
| 31 | items = items.reversed.toList(); |
| 32 | }); |
| 33 | } |
| 34 | |
| 35 | @override |
| 36 | Widget build(BuildContext context) { |
| 37 | return Scaffold( |
| 38 | body: SafeArea( |
| 39 | child: ListView.custom( |
| 40 | childrenDelegate: SliverChildBuilderDelegate( |
| 41 | (BuildContext context, int index) { |
| 42 | return KeepAliveItem(data: items[index], key: ValueKey<String>(items[index])); |
| 43 | }, |
| 44 | childCount: items.length, |
| 45 | findChildIndexCallback: (Key key) { |
| 46 | final ValueKey<String> valueKey = key as ValueKey<String>; |
| 47 | final String data = valueKey.value; |
| 48 | final int index = items.indexOf(data); |
| 49 | if (index >= 0) { |
| 50 | return index; |
| 51 | } |
| 52 | return null; |
| 53 | }, |
| 54 | ), |
| 55 | ), |
| 56 | ), |
| 57 | bottomNavigationBar: BottomAppBar( |
| 58 | child: Row( |
| 59 | mainAxisAlignment: MainAxisAlignment.center, |
| 60 | children: <Widget>[ |
| 61 | TextButton(onPressed: () => _reverse(), child: const Text('Reverse items')), |
| 62 | ], |
| 63 | ), |
| 64 | ), |
| 65 | ); |
| 66 | } |
| 67 | } |
| 68 | |
| 69 | class KeepAliveItem extends StatefulWidget { |
| 70 | const KeepAliveItem({required Key super.key, required this.data}); |
| 71 | |
| 72 | final String data; |
| 73 | |
| 74 | @override |
| 75 | State<KeepAliveItem> createState() => _KeepAliveItemState(); |
| 76 | } |
| 77 | |
| 78 | class _KeepAliveItemState extends State<KeepAliveItem> with AutomaticKeepAliveClientMixin { |
| 79 | @override |
| 80 | bool get wantKeepAlive => true; |
| 81 | |
| 82 | @override |
| 83 | Widget build(BuildContext context) { |
| 84 | super.build(context); |
| 85 | return Text(widget.data); |
| 86 | } |
| 87 | } |
| 88 |