Question

我的应用程序有脚手架。

但是我只想改变支架的主体。

通常我使用setState()来更改状态，但是在这种情况下，如何使用setState()或可以采取其他方法呢？

import 'package:flutter/material.dart';

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

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

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

  void onTapped() {
    print ("tapped");
    // I want to change only body of Scaffold like this
    // body: new Text("new body");
  };
class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: 
      GestureDetector(
        onTap: () => onTapped(),
        child:Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'You have pushed the button this many times:',
              ),
            ],
          ),
        ),
      ),
    );
  }
}

Answer 1

如果您只想在支架主体内设置setState，请将主体设置为有状态的窗口小部件，然后在该窗口小部件中调用setState。您可以通过扩展StatelessWidget或StatefulWidget来定义自己的无状态小部件和有状态小部件。由于Flutter如何分隔重建过程，将特定的东西定义为自己的窗口小部件而不是仅作为返回窗口小部件的方法很有用。如果支架的主体是其自己的窗口小部件，则在调用setState时将仅重建该窗口小部件。如果您按照其他答案的建议进行操作，则将重建MyHomePage，其中包括支架。另一方面，如果您定义范围较小的有状态窗口小部件，然后在该窗口小部件中调用setState（），则只会重建范围较小的窗口小部件。

例如：

import 'package:flutter/material.dart';

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

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

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

  @override
  Widget build(BuildContext context) {

    print('scaffold rebuilt');

    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: ScaffoldBody(),
    );
  }
}

class ScaffoldBody extends StatefulWidget {
  @override
  _ScaffoldBodyState createState() => _ScaffoldBodyState();
}

class _ScaffoldBodyState extends State<ScaffoldBody> {

  int timesTapped = 0;

  void onTapped() {
    setState(() {
      timesTapped++;
    });
  }

  @override
  Widget build(BuildContext context) {

    print('scaffold body rebuilt');

    return GestureDetector(
        onTap: onTapped,
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'You have pushed the button this many times: $timesTapped',
              ),
            ],
          ),
        ),
      );
  }
}

Answer 2

您可以创建变量Widget _scaffoldBody;来保存当前的脚手架主体。

为它设置一个初始值，然后在需要更改正文时调用setState。

类似这样的东西：

class _MyHomePageState extends State<MyHomePage> {
  Widget _scaffoldBody;

  @override
  void initState(){
    // Initialize it with the first body you want visible.
    _scaffoldBody = GestureDetector(
      onTap: () => onTapped(),
      child:Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
          ],
        ),
      ),
    );
  }

  // Note: move the onTapped method inside the state so you can call setState;
  void onTapped()
    // Call setState changing the body
    setState((){
      _scaffoldBody = Text("new body");
    });
  };

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: _scaffoldBody,
    );
  }
}

我可以使用setState更改小部件的主体吗？

2 个答案: