Question

有两个有状态的小部件。 MyHomePage的状态包含计数器。 MyHomePage将内容包装在第二个有状态小部件SubPage中。子页面具有一个子窗口小部件，其中包含来自MyHomePage的数据。

为解决此问题，计数器更改时，SubPage子级内部的第一个textwidget不会更新。

子页面外部的textwidget会按预期增加。

如果我们要更新内部有状态小部件的内容，我们该怎么办？

我们必须在那里使用一个有状态的小部件。在实际的应用程序中，此小部件具有真实的用例。

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: Column(
        children: <Widget>[
          SubPage(
            child: new Center(
              child: new Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  new Text(
                    'You have pushed the button this many times:',
                  ),
                  new Text(
                    '$_counter',
                    style: Theme.of(context).textTheme.display1,
                  ),
                ],
              ),
            ),
          ),
          new Text(
            '$_counter',
            style: Theme.of(context).textTheme.display1,
          ),
        ],
      ),

      floatingActionButton: new FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: new Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class SubPage extends StatefulWidget {
  SubPage({Key key, this.child}) : super(key: key);

  final Widget child;

  @override
  SubPageState createState() => new SubPageState(child);
}

class SubPageState extends State<SubPage> {
  final Widget child;

  SubPageState(this.child);

  @override
  Widget build(BuildContext context) {
    print("subpage build");
    return this.child;
  }
}

Answer 1

您不必将<!doctype html> <html> <head> <title> Home </title> <link href="mainCSS.css" rel="stylesheet" type="text/css" /> <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> </head> <body> <div class="wrapper"> <header> <div class="topnav" id="myTopnav">  <ul> <h1 class="first"><a href="MyWebsiteCSS.html">UrbanAero</a></h1> <li class="room"><a href="#">Rooms</a> <div class="subnav" id="mySubnav"> <ul class="boi"> <li><a href="#">Living room</a></li><br> <li><a href="#">Dining room</a></li><br> <li><a href="#">Home office and Study</a></li><br> <li><a href="#">Bedroom</a></li> <a href="javascript:void(0);" class="subIcon" onclick="subnavFunction();"><i class="fa fa-caret-down" aria-hidden="true"></i></a> </ul> </div> </li> <li><a href="#">lighting</a></li> <li><a href="#">Accessories</a></li> <li><a class="GreyText" href="ContactCSS.html">Contact</a></li> <li><a class="GreyText" href="AboutCSS.html">About Us</a></li> <li> <a href="javascript:void(0);" class="icon" onclick="myFunction()"></li> <li><i class="fa fa-bars"></i></a> </li> </ul> </div> </header> <div class="push"> </div> </div> <footer class="footer">©UrbanAero</footer> </body> </html>设置为状态字段。实际上，这是此错误的原因。这里的工作代码

child

有状态的小部件子项未更新

1 个答案: