// closer together (more dense) than on mobile platforms.
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: ‘Flutter Demo Home Page’),
);
}
}
//StatefulWidget有状态的widget,状态需要变化的，比如数字增加
//官方建议使用StatelessWidget，防止性能消耗
//MyHomePage类是标准的写法，最下面还重写了createState方法
class MyHomePage extends StatefulWidget {
//命名构造函数，调用父类
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() => _MyHomePageState();
}
class _MyHomePageState extends State {
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++;
});
}
//build是构建界面，渲染这个界面
@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 reru
《Android学习笔记总结+最新移动架构视频+大厂安卓面试真题+项目实战源码讲义》
【docs.qq.com/doc/DSkNLaERkbnFoS0ZF】 完整内容开源分享
nning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
//读取到Scaffold
return Scaffold(
appBar: 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: Text(widget.title),//这里的widget就是上面的MyHomePage
),
body: Center(//body是一个居中布局
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(//按照列进行布局，就是纵向布局
// Column is also a 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 painting” (press “p” in the console, choose the
// “Toggle Debug Paint” action from the Flutter Inspector in Android
// Studio, or the “Toggle Debug Paint” command in Visual Studio Code)
// 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,//因为是竖直布局，mainAxis是垂直布局
children: [//子元素有2个，2个Text
Text(
‘You have pushed the button this many times:’,
),
Text(
‘$_counter’,
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(//悬浮在界面上的button
onPressed: _incrementCounter,//点击事件调用_incrementCounter
tooltip: ‘Increment’,//长按的提升作用，没有实用意义
child: Icon(Icons.add),//设置的图标样式
), // This trailing comma makes auto-formatting nicer for build methods.