StatelessWidget, StatefulWidget, setState()
StatelessWidget
不會改變的靜態頁面，繼承StatelessWidget，並實作build()方法。
快速鍵，輸入stateless
把上面MaterialApp(…)全複製到build()方法中的return 後面。
在runApp()參數設成MainPage(自訂類別名)。
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import 'package:flutter/material.dart';
void main() {
runApp(MainPage());
}
class MainPage extends StatelessWidget {
const MainPage({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Base',
theme: ThemeData(scaffoldBackgroundColor: Colors.blue),
home: Scaffold(
appBar: AppBar(
title: Text('AppBar'),
),
body: Container(
child: Center(
child: Text('Body'),
),
),
bottomNavigationBar: Container(
color: Colors.amber,
height: 50,
child: Center(
child: Text('Bottom Navigation Bar'),
),
),
),
);
}
}
StatefulWidget
若畫面有Click按鈕，有互動，會影嚮畫面變化，要繼承StatefulWidget。
快速鍵，輸入stateful
建立二個類別，分別繼承StatefulWidget、State，步驟如下:
- 供外部讀取，繼承StatefulWidget
- 供內部私有使用，繼承 State<供外部讀取的類別名>
- 把會變動的內容，寫在_MainPageState類別，build()方法。
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import 'package:flutter/material.dart';
void main() {
runApp(MainPage());
}
class MainPage extends StatefulWidget {
MainPage({Key? key}) : super(key: key);
@override
_MainPageState createState() => _MainPageState();
}
class _MainPageState extends State<MainPage> {
int count = 0;
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Base',
theme: ThemeData(scaffoldBackgroundColor: Colors.blue),
home: Scaffold(
appBar: AppBar(
title: Text('AppBar'),
),
body: Container(
child: Row(
children: [
TextButton(
onPressed: () {
setState(() {
count++;
});
},
child: Text("Add"),
),
Text(count.toString()),
TextButton(
onPressed: () {
setState(() {
count--;
});
},
child: Text("Subtract"),
),
],
),
)),
);
}
}
