Flutter TextField 不遵循 ReorderableListView 中的 ListTiles

Question

I'm trying to use a TextFormField within a ReorderableListView and can't seem to get the text to follow the moving ListTile . Below is a minimally modified copy of the ReorderableListView sample code that reproduces the issue. All that's added is a list of Strings and a TextFormField per ListTile .

The example includes a Text widget that tracks with the movement of the ListTile . The difference I see with Text is that it is possible to update the Text constructor in the build method of the ListTile .

Using an itemBuilder: instead of the static children: property seems to make no difference.

What am I missing here? Thanks in advance!

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: const MyStatefulWidget(),
      ),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  final List<int> _items = List<int>.generate(50, (int index) => index);
  final List<String> _textValues = List<String>.generate(50, (int index) => '');

  @override
  Widget build(BuildContext context) {
    final ColorScheme colorScheme = Theme.of(context).colorScheme;
    final Color oddItemColor = colorScheme.primary.withOpacity(0.05);
    final Color evenItemColor = colorScheme.primary.withOpacity(0.15);

    return ReorderableListView(
      padding: const EdgeInsets.symmetric(horizontal: 40),
      children: <Widget>[
        for (int index = 0; index < _items.length; index += 1)
          ListTile(
            key: Key('$index'),
            tileColor: _items[index].isOdd ? oddItemColor : evenItemColor,
            title: Text('Item ${_items[index]}: ${_textValues[index]}'),
            subtitle: TextFormField(
              initialValue: _textValues[index],
              onChanged: (String? value) {
                setState(() {
                  _textValues[index] = value!;
                });
              },
              decoration: const InputDecoration(
                border: OutlineInputBorder(),
              ),
            ),
          ),
      ],
      onReorder: (int oldIndex, int newIndex) {
        setState(() {
          if (oldIndex < newIndex) {
            newIndex -= 1;
          }
          final int item = _items.removeAt(oldIndex);
          _items.insert(newIndex, item);
          final String textValue = _textValues.removeAt(oldIndex);
          _textValues.insert(newIndex, textValue);
        });
      },
    );
  }
}

Answer 1

It appears as though this works if I wrap the int and String in an object, and then use a single ObjectKey as the key for the ListTile . I guess the lesson here is that even if multiple lists of properties are in sync, some widgets cache or something and aren't properly rebuilt, while others are.

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: const MyStatefulWidget(),
      ),
    );
  }
}

class Item {
  int? item;
  String? text;

  Item(this.item, this.text);
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  final List<Item> _listItems =
      List<Item>.generate(50, (int index) => Item(index, ''));

  @override
  Widget build(BuildContext context) {
    final ColorScheme colorScheme = Theme.of(context).colorScheme;
    final Color oddItemColor = colorScheme.primary.withOpacity(0.05);
    final Color evenItemColor = colorScheme.primary.withOpacity(0.15);

    return ReorderableListView(
      padding: const EdgeInsets.symmetric(horizontal: 40),
      children: <Widget>[
        for (int index = 0; index < _listItems.length; index += 1)
          ListTile(
            key: ObjectKey(_listItems[index]),
            tileColor:
                _listItems[index].item!.isOdd ? oddItemColor : evenItemColor,
            title: Text(
                'Item ${_listItems[index].item}: ${_listItems[index].text}'),
            subtitle: TextFormField(
              initialValue: _listItems[index].text,
              onChanged: (String? value) {
                setState(() {
                  _listItems[index].text = value!;
                });
              },
              decoration: const InputDecoration(
                border: OutlineInputBorder(),
              ),
            ),
          ),
      ],
      onReorder: (int oldIndex, int newIndex) {
        setState(() {
          if (oldIndex < newIndex) {
            newIndex -= 1;
          }
          final Item listItem = _listItems.removeAt(oldIndex);
          _listItems.insert(newIndex, listItem);
        });
      },
    );
  }
}