如何在 Flutter 中清除 AnimatedList 中的所有项目

Question

我试图在 AnimatedList 上预先生成所有更新操作，就像我为 Android 中的 RecyclerView 适配器所做的那样。但是当我要清除所有数据时，我不知道该怎么做。

如果我这样做

setState(() {
  _data.clear();
});

然后后台数据被清除，但是 GlobalKey 的当前状态仍然不知道变化，并且上面没有clear() 方法。

补充代码

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        appBar: AppBar(title: Text('Update AnimatedList data')),
        body: BodyWidget(),
      ),
    );
  }
}

class BodyWidget extends StatefulWidget {
  @override
  BodyWidgetState createState() {
    return new BodyWidgetState();
  }
}

class BodyWidgetState extends State<BodyWidget> {

  // the GlobalKey is needed to animate the list
  final GlobalKey<AnimatedListState> _listKey = GlobalKey();

  // backing data
  List<String> _data = ['Horse', 'Cow', 'Camel', 'Sheep', 'Goat'];

  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        SizedBox(
          height: 400,
          child: AnimatedList(
            key: _listKey,
            initialItemCount: _data.length,
            itemBuilder: (context, index, animation) {
              return _buildItem(_data[index], animation);
            },
          ),
        ),
        RaisedButton(
          child: Text(
            'Clear all items',
            style: TextStyle(fontSize: 20),
          ),
          onPressed: () {
            _clearAllItems();
          },
        )
      ],
    );
  }

  Widget _buildItem(String item, Animation animation) {
    return SizeTransition(
      sizeFactor: animation,
      child: Card(
        child: ListTile(
          title: Text(
            item,
            style: TextStyle(fontSize: 20),
          ),
        ),
      ),
    );
  }

  void _clearAllItems() {
    _data.clear();
    // no such method
    _listKey.currentState.clear();
  }

}

Answer 1

您必须手动删除 _listKey.currentState 中的项目

示例代码：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        appBar: AppBar(title: Text('Update AnimatedList data')),
        body: BodyWidget(),
      ),
    );
  }
}

class BodyWidget extends StatefulWidget {
  @override
  BodyWidgetState createState() {
    return new BodyWidgetState();
  }
}

class BodyWidgetState extends State<BodyWidget> {
  // the GlobalKey is needed to animate the list
  final GlobalKey<AnimatedListState> _listKey = GlobalKey();

  // backing data
  List<String> _data = ['Horse', 'Cow', 'Camel', 'Sheep', 'Goat'];

  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        SizedBox(
          height: 400,
          child: AnimatedList(
            key: _listKey,
            initialItemCount: _data.length,
            itemBuilder: (context, index, animation) {
              return _buildItem(_data[index], animation);
            },
          ),
        ),
        RaisedButton(
          child: Text(
            'Clear all items',
            style: TextStyle(fontSize: 20),
          ),
          onPressed: () {
            _clearAllItems();
          },
        )
      ],
    );
  }

  Widget _buildItem(String item, Animation animation) {
    return SizeTransition(
      sizeFactor: animation,
      child: Card(
        child: ListTile(
          title: Text(
            item,
            style: TextStyle(fontSize: 20),
          ),
        ),
      ),
    );
  }

  void _clearAllItems() {
    for (var i = 0; i <= _data.length - 1; i++) {
      _listKey.currentState.removeItem(0,
          (BuildContext context, Animation<double> animation) {
        return Container();
      });
    }
    _data.clear();
  }
}

Answer 2

每次您将新密钥传递给 AnimatedList 小部件时，它都会重新创建其状态并在下一次使用全新的项目列表进行重建：

var _listKey = GlobalKey<AnimatedListState>();

void _clearAllItems() {
  _data.clear();
  setState(() => _listKey = GlobalKey());
}