## 推荐阅读
[《Flutter实战》7.2 数据共享（InheritedWidget）](https://book.flutterchina.club/chapter7/inherited_widget.html)
[Flutter知识点: InheritedWidget](https://www.jianshu.com/p/387e2454d590)
[Flutter状态管理(1)——InheritedWidget](https://cloud.tencent.com/developer/article/1506834)
## 状态管理
Flutter的状态管理分为两种：局部状态和全局状态。
* 局部状态：就是一个StatefulWidget可以搞定的；其他Widget不需要知道你的状态，你也不需要依赖其他Widget的状态
* 全局状态：整个app很多页面都需要用到的状态，比如是否登录了，用户名、用户id等；
Flutter状态管理系列主要指的是全局状态的管理，主要介绍的几种实现方式有：
* InheritedWidget
* StreamBuilder
* Provider
简单来说，InheritedWidget下面的Widget都可以获取到该Widget持有的状态。
Theme这个源码大家可以去看一下 ，对理解 InheritedWidget会有比较大的帮助
## Demo
~~~
import 'package:flutter/material.dart';
class InheritedOneData{
int number = 1;
@override
bool operator ==(other) {
return number == (other as InheritedOneData).number;
}
}
class InheritedWidgetOne extends InheritedWidget {
final InheritedOneData data;
InheritedWidgetOne({@required this.data, Widget child}) : super(child: child);
static InheritedWidgetOne of(BuildContext context) {
return context.inheritFromWidgetOfExactType(InheritedWidgetOne);
}
@override
bool updateShouldNotify(InheritedWidgetOne oldWidget) {
return oldWidget.data != data;
}
}
class InheritedWidgetDemo extends StatelessWidget {
@override
Widget build(BuildContext context) {
Scaffold scaffold = Scaffold(
appBar: AppBar(
title: new Text("ScrollDemoPage"),
),
body: new Container(
child: new ContentView(),
),
);
return new InheritedWidgetOne(
data: new InheritedOneData(),
child: scaffold,
);
}
}
class ContentView extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new Column(
children: <Widget>[
new ShowView(),
new AddView(),
],
);
}
}
class ShowView extends StatelessWidget {
@override
Widget build(BuildContext context) {
InheritedOneData data = InheritedWidgetOne.of(context).data;
return new Text("${data.number}");
}
}
class AddView extends StatefulWidget {
@override
State<AddView> createState() {
return new AddViewViewState();
}
}
class AddViewViewState extends State<AddView> {
@override
Widget build(BuildContext context) {
return new RaisedButton(onPressed: () {
setState(() {
InheritedOneData data = InheritedWidgetOne.of(context).data;
data.number ++ ;
});
}, child: Text("add"));
}
}
~~~
其实核心方法就两个
* inheritFromWidgetOfExactType：通过子widget可以通过BuildContext.inheritFromWidgetOfExactType(InheritedWidget)获得到InheritedWidget的实例，从而随时随地获取全局状态的值
* updateShouldNotify
