flutter中的视图Widget像Android中的Activity一样存在生命周期，生命周期的回调函数体都在State中。
组件State的生命周期整理：
创建阶段
Log所示：
image.png
Widget状态改变
操作：横竖屏切换
Log所示：
其他生命周期并没有执行
竖屏切换到横屏执行2次
横屏切换到竖屏执行2次
image.png
App切后台，再切回来
Log所示：
image.png
销毁阶段
Log所示：
image.png
流程如图：
![]()
image.png
image.png
代码：
import 'package:flutter/material.dart';
class LifecycleAppPage extends StatefulWidget {
@override
State<StatefulWidget> createState() {
return new _LifecycleAppPageState('构造函数');
}
}
class _LifecycleAppPageState extends State<LifecycleAppPage>
with WidgetsBindingObserver {
String str;
int count = 0;
_LifecycleAppPageState(this.str);
@override
void initState() {
print(str);
print('initState');
super.initState();
WidgetsBinding.instance.addObserver(this);
}
@override
void didChangeDependencies() {
print('didChangeDependencies');
super.didChangeDependencies();
}
@override
void didUpdateWidget(LifecycleAppPage oldWidget) {
print('didUpdateWidget');
super.didUpdateWidget(oldWidget);
}
@override
void deactivate() {
print('deactivate');
super.deactivate();
}
@override
void dispose() {
print('dispose');
WidgetsBinding.instance.removeObserver(this);
super.dispose();
}
@override
void didChangeAppLifecycleState(AppLifecycleState state) {
switch (state) {
case AppLifecycleState.inactive:
print('AppLifecycleState.inactive');
break;
case AppLifecycleState.paused:
print('AppLifecycleState.paused');
break;
case AppLifecycleState.resumed:
print('AppLifecycleState.resumed');
break;
case AppLifecycleState.suspending:
print('AppLifecycleState.suspending');
break;
}
super.didChangeAppLifecycleState(state);
}
@override
Widget build(BuildContext context) {
print('build');
return new Scaffold(
appBar: new AppBar(
title: new Text('lifecycle 学习'),
centerTitle: true,
),
body: new OrientationBuilder(
builder: (context, orientation) {
return new Center(
child: new Text(
'当前计数值：$count',
style: new TextStyle(
color: orientation == Orientation.portrait
? Colors.blue
: Colors.red),
),
);
},
),
floatingActionButton: new FloatingActionButton(
child: new Text('click'),
onPressed: () {
count++;
setState(() {});
}),
);
}
}
class LifecyclePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
// TODO: implement build
return new Scaffold(
body: new LifecycleAppPage(),
);
}
}
