flutter - Int 在热重载之前不会刷新

Question

基本上，我得到了颤振工作和一切，我正在努力学习框架......

为了学习这个框架，我决定做一个简单的应用程序，有一个大按钮，上面写着“你已经按下按钮____很多次”

除了一件事之外，该程序的工作方式： int 不刷新

例如，如果您没有按下按钮（在启动时），它会说“您已经多次按下按钮：0”

现在假设我单击按钮 3 次...（单击）（单击）（单击）

它仍然显示“您已多次按下按钮：0”

所以我尝试热重新加载它，然后它才会更新并说“你已经多次按下按钮：3”

我的代码有问题吗？

谢谢

代码从下面开始：

import 'package:flutter/material.dart';


int _test1 = 0;

void _add(){
      _test1 = _test1+1;
      //print(_test1);

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


class MyApp extends StatelessWidget {
  @override
  int _count = 5;
  Widget build(BuildContext context) {

    return MaterialApp(
      title: 'Welcome to Flutter',
      theme: new ThemeData(          
        primaryColor: Colors.tealAccent,
        textSelectionColor: Colors.amberAccent,
      ),  

      home: Scaffold(
        appBar: AppBar(
          title: Text('Welcome to My Learning App'),
        ),

        body: Center(

          child: Column(children: <Widget>[
            Count(),

            Text(
              "You pressed the purple button this many times: "+_test1.toString()
              ),
          ],
          ),


        ),
      ),
    );
  }
}

class CountState extends State<Count> {
  @override

  Widget build(BuildContext context) {

    //return Text("You clicked button this many times: "+_test1.toString());
    return IconButton(
       icon: Icon(Icons.add_circle),
       tooltip: 'Just press the button',
       color: Colors.purple[300],
       iconSize: 150.0,
        onPressed: (){_add();},
      );  }
}

class Count extends StatefulWidget {
  @override
  CountState createState() => new CountState();
}

标签： flutter

Answer 1

如果您创建一个全新的应用程序，它基本上可以满足您的需求。这是来自全新应用程序的代码：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or press Run > Flutter Hot Reload in IntelliJ). Notice that the
        // counter didn't reset back to zero; the application is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

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

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return new Scaffold(
      appBar: new AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: new Text(widget.title),
      ),
      body: new Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: new Column(
          // Column is also layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug paint" (press "p" in the console where you ran
          // "flutter run", or select "Toggle Debug Paint" from the Flutter tool
          // window in IntelliJ) to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text(
              'You have pushed the button this many times:',
            ),
            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.
    );
  }
}

重要的部分是setState(() => ...计数器整数在继承的类中State。这样想 - 有一种状态在，并且仅在，中改变setState。然后在构建函数中使用此状态，并且每次更改状态时都会创建构建函数。