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492b6f7ddf
The documentation for using `findChildIndexCallback` recommends using `indexOf`, but that causes [this line](05259ca938/packages/flutter/lib/src/rendering/sliver_multi_box_adaptor.dart (L259)) to throw in debug mode, and when using `SliverList`, it breaks the render.
This PR changes the usage to check if the index is not negative before using it, and changes to return `null` instead if the child wasn't able to be found.
There's the related issue #107123, but this doesn't actually fix it.
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This PR has been updated to add the snippets that were used in the `findChildIndexCallback` comment as examples with proper tests, as well as updating the comment to reference the new examples.
96 lines
2.5 KiB
Dart
96 lines
2.5 KiB
Dart
// Copyright 2014 The Flutter Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'package:flutter/material.dart';
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/// Flutter code sample for a [PageView] using the `findChildIndexCallback` argument.
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void main() => runApp(const PageViewExampleApp());
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class PageViewExampleApp extends StatelessWidget {
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const PageViewExampleApp({super.key});
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@override
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Widget build(BuildContext context) {
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return const MaterialApp(home: PageViewExample());
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}
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}
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class PageViewExample extends StatefulWidget {
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const PageViewExample({super.key});
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@override
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State<PageViewExample> createState() => _PageViewExampleState();
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}
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class _PageViewExampleState extends State<PageViewExample> {
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List<String> items = <String>['1', '2', '3', '4', '5'];
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void _reverse() {
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setState(() {
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items = items.reversed.toList();
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});
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}
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@override
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Widget build(BuildContext context) {
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return Scaffold(
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appBar: AppBar(title: const Text('PageView Sample')),
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body: SafeArea(
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child: PageView.custom(
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childrenDelegate: SliverChildBuilderDelegate(
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(BuildContext context, int index) {
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return KeepAliveItem(
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data: items[index],
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key: ValueKey<String>(items[index]),
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);
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},
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childCount: items.length,
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findChildIndexCallback: (Key key) {
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final ValueKey<String> valueKey = key as ValueKey<String>;
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final String data = valueKey.value;
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final int index = items.indexOf(data);
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if (index >= 0) {
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return index;
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}
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return null;
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},
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),
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),
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),
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bottomNavigationBar: BottomAppBar(
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child: Row(
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mainAxisAlignment: MainAxisAlignment.center,
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children: <Widget>[
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TextButton(
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onPressed: () => _reverse(),
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child: const Text('Reverse items'),
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),
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],
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),
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),
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);
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}
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}
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class KeepAliveItem extends StatefulWidget {
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const KeepAliveItem({super.key, required this.data});
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final String data;
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@override
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State<KeepAliveItem> createState() => _KeepAliveItemState();
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}
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class _KeepAliveItemState extends State<KeepAliveItem>
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with AutomaticKeepAliveClientMixin {
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@override
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bool get wantKeepAlive => true;
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@override
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Widget build(BuildContext context) {
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super.build(context);
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return Text(widget.data);
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}
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}
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