默认项目main.dart
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@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();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
分析
1. 导入包文件
import 'package:flutter/material.dart'
此处代码主要是导入 material UI框架,Flutter默认提供一整套material风格的UI框架.
2. 入口函数
void main() => runApp(MyApp());
和其他开发类似,通过main函数作为应用程序入口启动应用
3. 应用结构
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
-
MyApp类代表Flutter应用，它继承了StatelessWidget类，这也就意味着应用本身也是一个widget - 在Flutter中，大多数东西都是
widget（后同“组件”或“部件”），包括对齐(alignment)、填充(padding)和布局(layout)等，它们都是以widget的形式提供 - Flutter在构建页面时，会调用组件的
build方法，widget的主要工作是提供一个build()方法来描述如何构建UI界面（通常是通过组合、拼装其它基础widget） -
MaterialApp是Material库中提供的Flutter APP框架，通过它可以设置应用的名称、主题、语言、首页及路由列表等。MaterialApp也是一个widget -
Scaffold是Material库中提供的页面脚手架，它包含导航栏和Body以及FloatingActionButton,路由默认都是通过Scaffold创建 - home 应用的首页
首页
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> { ...}
-
MyHomePage继承StatefulWidget -
StatefulWidget标示的是一个有状态组件(Stateful widget),相对的StatelessWidget无状态组件(Stateless widget) - Stateful widget至少由两个类组成：①StatefulWidget类 ②State类
- _MyHomePageState类是MyHomePage类对应的状态类
state类
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.display1,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
- 定义一个技术变量
_counter - 实现一个方法,用来点击按钮后执行计数
_incrementCounter(), -
setState用来告诉flutter状态改变, 通知build方法刷新界面 -
build中实现三个组件
-- 1.scaffoldMaterial组件库中提供的一个组件
-- 2.body实现一个Center组件,将子控件对齐屏幕中心,Column的作用是将其所有子组件沿屏幕垂直方向依次排列
-- 3.floatingActionButton实现一个悬浮按钮,添加点击事件
