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.orange,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(),
);
}
}
class Counter extends ChangeNotifier {
// 这里也可以使用with来进行实现
int _count = 0; //数值计算
int get count => _count;
addCount() {
_count++;
notifyListeners();
}
}
Counter _counter = Counter();
class MyHomePage extends StatefulWidget {
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State {
@override
void initState() {
super.initState();
_counter.addListener(() {
// 数值改变的监听
print('YM--->新数值:${_counter.count}');
});
}
@override
void dispose() {
super.dispose();
_counter.dispose(); //移除监听
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(title: Text('Hello')),
body: Center(
child: Container(
child: RaisedButton(onPressed: () {
_counter.addCount();
}, child: Text('计数'),),
),
),
);
}
}
创建一个继承ChangeNotifier的类
class Counter extends ChangeNotifier {
// 这里也可以使用with来进行实现
int _count = 0; //数值计算
int get count => _count;
addCount() {
_count++;
notifyListeners();
}
}
在外边创建一个持久化的对象
Counter _counter = Counter();
在initState的时候注册Listener @override
void initState() {
super.initState();
_counter.addListener(() {
// 数值改变的监听
print('YM--->新数值:${_counter.count}');
});
}
dispose的时候dispose掉，然后就不能用了
@override
void dispose() {
super.dispose();
_counter.dispose(); //移除监听，再调用的话会崩溃
}
调用_counter.addCount();
_counter.addCount(); // 里面调用了notifyListeners()方法
