（一）InheritedWidget （自上而下）放在根组件

跳转页面去另一个页面可以覆盖当前页面，回来的时候值还存在（后期你就明白了）

状态自上而下传递数据。

<比如说我们的 MediaQuery.of(context)也使用了>

可以共享数据，或者你监听数据变化然后改变缓存中的值。

应为我们改变状态需要在 StatefulWidget 才能改变状态，所以我们在继承 InheritedWidget 的时候在 StatefulWidget 中调用。

UserBean

class UserBean {
  String name;
  String address;
  UserBean({this.address,this.name});
  String toString(){
    return "UserBean{name: $name, address : $address}";
  }
}

UserInfoWidget

import 'package:YuWeiFlutterApp/src/userbean.dart';
import 'package:flutter/widgets.dart';
class UserInfoInheritedWidget extends InheritedWidget {
  UserBean userBean;
  Function updateInfo;
  UserInfoInheritedWidget({
    this.userBean,
    Key key,
    Widget child,
    this.updateInfo,
  }):super(key: key, child: child);
  void updateUserBean(String username, String useraddress){
    updateInfo(username,useraddress);
  }
  @override
  bool updateShouldNotify(UserInfoInheritedWidget oldWidget) { 
    return oldWidget.userBean != userBean;
    // if( oldWidget.userBean.name != userBean.name || oldWidget.userBean.address != userBean.address ){
    //   return true;  //  更新视图
    // } 
    // return false;  // 不更新视图
  }
}
class UserInfoWidget extends StatefulWidget {
  UserBean userBean;
  Widget child;
  UserInfoWidget({this.userBean, Key key , this.child}) : super(key: key);
  static UserInfoInheritedWidget of( BuildContext context ){
    return context.dependOnInheritedWidgetOfExactType<UserInfoInheritedWidget>();
  }
  @override
  _UserInfoWidgetState createState() => _UserInfoWidgetState();
}
class _UserInfoWidgetState extends State<UserInfoWidget> {
  void _updata(String name , String address){ 
    widget.userBean = UserBean(name: name , address:  address);
    setState(() {
    });
  }
  @override
  Widget build(BuildContext context) {
    return UserInfoInheritedWidget(
      userBean: widget.userBean,
      child: widget.child,
      updateInfo : _updata
    );
  }
}

IndexInHeritedWidget 页面 【使用值】

import 'package:YuWeiFlutterApp/src/index_textPage.dart';
import 'package:YuWeiFlutterApp/src/userInfo_widhet.dart'; 
import 'package:flutter/material.dart';
class IndexInHeritedWidget extends StatefulWidget {
  @override
  _IndexInHeritedWidgetState createState() => _IndexInHeritedWidgetState();
}
class _IndexInHeritedWidgetState extends State<IndexInHeritedWidget> {
  @override
  Widget build(BuildContext context) {
    print("page1");
    return Scaffold(
      appBar: AppBar(
        title: Text("Page_1"),
      ),
      body: Container(
        width: double.infinity,
        height: double.infinity,
        color: Color(0x88f1f1f1),
        child: Column(
          children: [
            SizedBox(height: 10.0,),
            Text(UserInfoWidget.of(context).userBean.name),   /// 使用
            SizedBox(height: 10.0,),
            Text(UserInfoWidget.of(context).userBean.address), /// 使用
            SizedBox(height: 500.0,),
            FloatingActionButton(
              onPressed: (){ 
                Navigator.of(context).push(MaterialPageRoute(
                  builder: (context) => IndexTextPage()
                ));
              },
              child: Icon(Icons.chevron_right),
            )
          ],
        ),
      ),  
    );
  }
}

IndexTextPage 页面 【使用值 和 改变值】

import 'package:YuWeiFlutterApp/src/index_inheritedwidget.dart';
import 'package:YuWeiFlutterApp/src/userInfo_widhet.dart';
import 'package:YuWeiFlutterApp/src/userbean.dart';
import 'package:YuWeiFlutterApp/src/util/navigator_util.dart';
import 'package:flutter/material.dart';
class IndexTextPage extends StatefulWidget {
  @override
  _IndexTextPageState createState() => _IndexTextPageState();
}
class _IndexTextPageState extends State<IndexTextPage> {
  @override
  Widget build(BuildContext context) {
    print("page2");
    return Scaffold(
      appBar: AppBar(
        title: Text("Page_2"),
      ),
      body: Container(
        width: double.infinity,
        height: double.infinity,
        color: Color(0x88f1f1f1),
        child: Column(
          children: [
            SizedBox(height: 200.0,),
            Text(UserInfoWidget.of(context).userBean.name),
            SizedBox(height: 10.0,),
            Text(UserInfoWidget.of(context).userBean.address),
            SizedBox(height: 290.0,),
            FloatingActionButton(
              onPressed: (){
                UserInfoWidget.of(context).updateUserBean("Flutter change", "Child change");  // 改变。
              },
              child: Icon(Icons.error),
            ),
            SizedBox(height: 20.0,),
          ],
        ),
      ),  
    );
  }
}

在根部使用

  Widget build(BuildContext context) {
    return UserInfoWidget(
      userBean: UserBean(
        name: "Flutter inheritedWidget" ,
        address: "China"
      ),
      child: MaterialApp(
         home: IndexInHeritedWidget(),
       ),
    );
  }