（二）Notification （自下而上）更改数据

《单页面使用》

在需要使用的页面来用。

比如说在，评论列表中更新数据，则我们就可以使用这样的方法来，在当页面操作数据不能共享。

import 'package:YuWeiFlutterApp/src/customNotification.dart'; 
import 'package:YuWeiFlutterApp/src/userbean.dart'; 
import 'package:flutter/material.dart';
class IndexInHeritedWidget extends StatefulWidget {
  @override
  _IndexInHeritedWidgetState createState() => _IndexInHeritedWidgetState();
}
class _IndexInHeritedWidgetState extends State<IndexInHeritedWidget> {
  UserBean userBean = UserBean(name: "default", address: "default");
  num i = 1;
  @override
  Widget build(BuildContext context) {
    print("page1");
    return Scaffold(
      appBar: AppBar(
        title: Text("Page_1"),
      ),
      body: NotificationListener<CustomNotification>(
        ///CustomNotification(UserBean( 
        ///   name : "Flutter custom Notification",  
        ///   address: "China") 
        ///).dispatch(context);
        onNotification: (data){  // data 是监听 CustomNotification 变化的数据，如下面改变了的
          userBean = data.userBean;
          setState(() {
          });
          return true;
        },
      child : Builder(
        builder: (context) => Container(
           width: double.infinity,
           height: double.infinity,
           color: Color(0x88f1f1f1),
           child: Column(
             children: [
               SizedBox(height: 10.0,),
               Text( userBean.name ),
               SizedBox(height: 10.0,),
               Text( userBean.address ),
               SizedBox(height: 200.0,),
               FloatingActionButton(
                 onPressed: (){ 
                    CustomNotification(UserBean(
                      name : "Flutter custom Notification $i", 
                      address: "China $i")
                    ).dispatch(context);
                   /// 当 dispatch 的时候我们就会往上找，直到找到NotificationListener的onNotification然后改变值。
                    setState(() {
                      i++;
                    });
                 },
                 child: Icon(Icons.add_alert_outlined),
               ),
               SizedBox(height: 200.0,),
             ],
           ),
         ),
      )
      ),
    );
  }
}

CustomNotification

import 'package:YuWeiFlutterApp/src/userbean.dart';
import 'package:flutter/material.dart';
// Notification
class CustomNotification extends Notification {
  UserBean userBean;
  CustomNotification(this.userBean);
}