Stream

StreamBuilder(

　　Stream:_StreamDemo.Stream,

　　builder:(context, snapshot){

　　　　return Text('${snapshot.data}');

　　},

),

 

 

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

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Stream study'),
        ),
        body: StreamDemoHomeState(),
      ),
    );
  }
}

class StreamDemoHomeState extends StatefulWidget {
  @override
  _StreamDemoHomeStateState createState() => _StreamDemoHomeStateState();
}

class _StreamDemoHomeStateState extends State<StreamDemoHomeState> {
  StreamSubscription _streamDemoSubscription;
  StreamController<String> _streamDemo;
  @override
  void dispose() {
    // TODO: implement dispose
    _streamDemo.close();
    super.dispose();
  }
  @override
  void initState() {
    super.initState();
    // TODO: implement initState
    _streamDemo =StreamController<String>();
    //Stream<String> _streamDemo=Stream.fromFuture(fetchData());
    print('Start listening on a stream');
    _streamDemoSubscription=_streamDemo.stream.listen(onData,onError: onError, onDone: onDone);
    print('Initilization complete');
  }

  void onData(String data){
    print('$data');
  }
  void onError(error){
    print('Error:$error');
  }
  void onDone(){
    print('done');
  }
  Future<String> fetchData()async{
    await Future.delayed(Duration(seconds: 5));
    return 'hello ~';
  }
  void _pauseStream(){
    print('Pause subscription');
    _streamDemoSubscription.pause();
  }
  void _resumeStream(){
    print('Resume subscription');
    _streamDemoSubscription.resume();
  }
  void _cancelStream(){
    print('Cancel subscription');
    _streamDemoSubscription.cancel();
  }
  void _addDataToStream()async{
    print('add data to stream');
    String data=await (fetchData());
    _streamDemo.add(data);
  }
  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        child: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            FlatButton(
              onPressed:_addDataToStream,
              child: Text('add'),
            ),
            FlatButton(
              onPressed:_pauseStream,
              child: Text('pause'),
            ),
            FlatButton(
              onPressed: _resumeStream,
              child: Text('resume'),
            ),
            FlatButton(
              onPressed: _cancelStream,
              child: Text('cancel'),
            ),
          ],
        ),
      ),
    );
  }
}