ListView中如何维护widget的状态？

Question

我有一个可点击的小部件列表[即 MarkWidget]，当点击小部件时，小部件的状态会发生变化。但是当列表滚动到底部并滚动回顶部时，所有小部件的状态都会重置为默认值。

如何停止/强制颤动在滚动后不重绘列表中的现有小部件？

例如： 如果我单击 ITEM 1，颜色会从绿色变为红色，但如果滚动到底部并滚动回顶部，则 ITEM 1 颜色会变回绿色。 如果在不考虑滚动的情况下单击它，我需要 ITEM 1 颜色为红色。

这里是代码：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomeScreen(),
      theme: ThemeData(
        platform: TargetPlatform.android,
      ),
    );
  }
}

class HomeScreen extends StatefulWidget {
  @override
  _HomeScreenState createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  List<Widget> _widgetList = List.generate(
    30,
    (index) => MarkWidget(
          key: Key('ITEM $index'),
          title: 'ITEM $index',
        ),
  );

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("My List"),
      ),
      body: ListView.builder(
        key: new Key("my_list"), //new

        itemBuilder: (BuildContext context, int index) {
          return _widgetList[index];
        },
        itemCount: _widgetList.length,
      ),
    );
  }
}

class MarkWidget extends StatefulWidget {
  final String title;

  const MarkWidget({Key key, this.title}) : super(key: key);

  @override
  _MarkWidgetState createState() => _MarkWidgetState();
}

class _MarkWidgetState extends State<MarkWidget> {
  bool _checked = false;

  @override
  Widget build(BuildContext context) {
    return FlatButton(
      onPressed: () {
        setState(() {
          _checked = !_checked;
        });
      },
      child: Container(
        padding: EdgeInsets.all(10.0),
        margin: EdgeInsets.all(10.0),
        decoration: BoxDecoration(
          borderRadius: BorderRadius.all(
            Radius.circular(5.0),
          ),
          color: _checked ? Colors.red : Colors.green,
        ),
        child: Text(
          "${widget.title}",
          style: TextStyle(
            color: Colors.white,
            decoration: _checked ? TextDecoration.lineThrough : TextDecoration.none,
          ),
        ),
      ),
    );
  }
}

Answer 1

将AutomaticKeepAliveClientMixin mixin 添加到StatefulWidget（项目小部件）的State，覆盖wantKeepAlive 方法并返回true。

 class _MarkWidgetState extends State<MarkWidget> with AutomaticKeepAliveClientMixin{
   ...

   @override
   bool get wantKeepAlive => true;
  }

更多信息在这里：https://docs.flutter.io/flutter/widgets/AutomaticKeepAliveClientMixin-mixin.html