Flutter-从其他小部件调用setState（）

• Z时代
• 2024-01-10
• 分类：问答

是否有可能调用setState()其他部件尤其是小部件（嵌入在其它部件）的onPressed()方法，所以只能 小部件是重绘？

我想单击按钮，然后查看“ MyTextWidget”的状态进行更改。布局的其余部分相同，没有任何更改，因此不应重写。

这是我的代码：

import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Timer',
      theme: new ThemeData(
        primaryColor: Colors.grey.shade800,
      ),
      home: new MyHomePage(),
    );
  }
}
class MyHomePage extends StatelessWidget {
  int _seconds = 1;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("title"),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: <Widget>[
          MyTextWidget(), //just update this widget
          Divider(),
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: <Widget>[
              IconButton(
                icon: Icon(Icons.add_circle),
                onPressed: _addPressed,
                iconSize: 150.0,
              ),
              IconButton(
                icon: Icon(Icons.remove_circle),
                onPressed: ()=> print("to be implemented"),
                iconSize: 150.0,
              ),
            ],
          )
        ],
      ),
    );
  }
  void _addPressed() {
    //somehow call _updateSeconds()
  }
}

这是我要更新的全状态MyTextWidget。

class MyTextWidget extends StatefulWidget{
  @override
  _MyTextWidgetState createState() => _MyTextWidgetState();
}
class _MyTextWidgetState extends State<MyTextWidget> {
  int secondsToDisplay = 0;
  void _updateSeconds(int newSeconds) {
    setState(() {
      secondsToDisplay = newSeconds;
    });
  }
  @override
  Widget build(BuildContext context) {
    return Text(
      secondsToDisplay.toString(),
      textScaleFactor: 5.0,
    );
  }
}

我想要实现的目标似乎很简单，但我无法弄清楚。想象一下，如果“

MyTextWidget”埋在巨大的布局树中，并且每次我想对其进行更新时，都需要重新绘制整个树。

回答：

这是使用流的可能解决方案：

import 'dart:async';
import 'package:flutter/material.dart';
void main() => runApp(new MyApp());
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Timer',
      theme: new ThemeData(
        primaryColor: Colors.grey.shade800,
      ),
      home: new MyHomePage(),
    );
  }
}
class MyHomePage extends StatelessWidget {
  StreamController<int> _controller = StreamController<int>();
  int _seconds = 1;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("title"),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: <Widget>[
          MyTextWidget(stream: _controller.stream), //just update this widget
          Divider(),
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: <Widget>[
              IconButton(
                icon: Icon(Icons.add_circle),
                onPressed: _addPressed,
                iconSize: 150.0,
              ),
              IconButton(
                icon: Icon(Icons.remove_circle),
                onPressed: ()=> _controller.add(_seconds++),
                iconSize: 150.0,
              ),
            ],
          )
        ],
      ),
    );
  }
  void _addPressed() {
    //somehow call _updateSeconds()
  }
}
class MyTextWidget extends StatefulWidget{
  final Stream<int> stream;
  MyTextWidget({this.stream});
  @override
  _MyTextWidgetState createState() => _MyTextWidgetState();
}
class _MyTextWidgetState extends State<MyTextWidget> {
  int secondsToDisplay = 0;
  void _updateSeconds(int newSeconds) {
    setState(() {
      secondsToDisplay = newSeconds;
    });
  }
  @override
  void initState() {
    super.initState();
    widget.stream.listen((seconds) {
      _updateSeconds(seconds);
    });
  }
  @override
  Widget build(BuildContext context) {
    return Text(
      secondsToDisplay.toString(),
      textScaleFactor: 5.0,
    );
  }
}

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