Strem_01

import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:ui';

void main()=>runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {

  @override
  void initState() {
    // TODO: implement initState
    print('Create a Stream');
    Stream<String> _stream=Stream.fromFuture(fetchData());//创建一个Stream，并且给Stream赋值；
    _stream.listen(onData, onError:onError, onDone:onDone);//创建一个监听，包含三个监听方法；
    print('Start Listning Stream');
    super.initState();
  }
//下面这个函数是给Stream赋值用的；
  Future<String> fetchData()async{
    await Future.delayed(Duration(seconds:3));
    return 'Hello World';
  }
//下面这三个方法是监视器内部包含的三种监听方法：
  onData(String data){print('$data');}
  onError(error){print('$error');}
  onDone(){print('done');}
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('为人民服务',style: TextStyle(fontSize: 18,fontWeight: FontWeight.bold),),
        centerTitle: true,
      ),
    );
  }
}