默認項目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. 導入包文件
import 'package:flutter/material.dart'
此處代碼主要是導入 material UI框架,Flutter默認提供一整套material風格的UI框架.
2. 入口函數(shù)
void main() => runApp(MyApp());
和其他開發(fā)類似,通過main函數(shù)作為應用程序入口啟動應用
3. 應用結構
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類代表Flutter應用店归，它繼承了StatelessWidget類，這也就意味著應用本身也是一個widget - 在Flutter中，大多數(shù)東西都是
widget（后同“組件”或“部件”），包括對齊(alignment)、填充(padding)和布局(layout)等烦粒，它們都是以widget的形式提供 - Flutter在構建頁面時，會調(diào)用組件的
build方法，widget的主要工作是提供一個build()方法來描述如何構建UI界面（通常是通過組合峦树、拼裝其它基礎widget） -
MaterialApp是Material庫中提供的Flutter APP框架，通過它可以設置應用的名稱旦事、主題魁巩、語言、首頁及路由列表等姐浮。MaterialApp也是一個widget -
Scaffold是Material庫中提供的頁面腳手架谷遂，它包含導航欄和Body以及FloatingActionButton,路由默認都是通過Scaffold創(chuàng)建 - home 應用的首頁
首頁
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繼承StatefulWidget -
StatefulWidget標示的是一個有狀態(tài)組件(Stateful widget),相對的StatelessWidget無狀態(tài)組件(Stateless widget) - Stateful widget至少由兩個類組成：①StatefulWidget類 ②State類
- _MyHomePageState類是MyHomePage類對應的狀態(tài)類
state類
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.
);
}
}
- 定義一個技術變量
_counter - 實現(xiàn)一個方法,用來點擊按鈕后執(zhí)行計數(shù)
_incrementCounter(), -
setState用來告訴flutter狀態(tài)改變, 通知build方法刷新界面 -
build中實現(xiàn)三個組件
-- 1.scaffoldMaterial組件庫中提供的一個組件
-- 2.body實現(xiàn)一個Center組件,將子控件對齊屏幕中心,Column的作用是將其所有子組件沿屏幕垂直方向依次排列
-- 3.floatingActionButton實現(xiàn)一個懸浮按鈕,添加點擊事件
