dart - ExpansionTile 不保持状态

Question

以下问题:我有一个列表 ExpansionTiles效果很好。我面临的唯一问题是，滚动到 View 之外的展开的 ExpansionTile 在再次滚动到 View 后将不再展开。这会导致不良的用户体验以及一种“跳跃式”滚动。

文档说明如下:

When used with scrolling widgets like ListView, a unique key must be specified to enable the ExpansionTile to save and restore its expanded state when it is scrolled in and out of view.

虽然这不起作用。到目前为止，我还没有找到任何方法来完成这项工作。
这是到目前为止的代码:

import 'package:flutter/material.dart';

void main() {
  runApp(new MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'ExpansionTile Test',
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List<Widget> _getChildren() {
    List<Widget> elements = [];
    for (int i = 0; i < 20; i++) {
      elements.add(new ListChild());
    }
    return elements;
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('ExpansionTile Test'),
      ),
      body: new ListView(
        children: _getChildren(),
      ),
    );
  }
}

class ListChild extends StatefulWidget {
  @override
  State createState() => new ListChildState();
}

class ListChildState extends State<ListChild> {
  GlobalKey<ListChildState> _key = new GlobalKey();
  @override
  Widget build(BuildContext context) {
    return new ExpansionTile(
      key: _key,
      title: const Text('Test Tile'),
      children: <Widget>[
        const Text('body'),
      ],
    );
  }
}

Answer 1

使用 PageStorageKey 而不是 GlobalKey。