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

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> {
  StreamController<String> _streamController;
  StreamSubscription _streamSubsctiption;
  StreamSink _streamSink;

  @override
  void dispose() {
    // TODO: implement dispose
    _streamController.close();
    super.dispose();
  }

  @override
  void initState() {
    // TODO: implement initState
    print('Create a Stream');
    _streamController=StreamController<String>();
    _streamSubsctiption=_streamController.stream.listen(onData);
    _streamSink=_streamController.sink;
    addDataToStream(){
      _streamSink.add(fetchData());
    }
    print('Start Listning Stream');
    super.initState();
  }

  Future<String> fetchData()async{
    List<String> _listString=[
      'a','b','c''d','e','f''g','h','i''j','k','l''m','n','o','p''q'
    ];
    int count=Random().nextInt(10);
    await Future.delayed(Duration(seconds:1));
    return _listString[count];
  }

  void _addDataToStream()async{
    print('add data to stream');
    String data=await (fetchData());
    _streamController.add(data);
  }

  onData(String data){print('$data');}
  onError(error){print('$error');}
  onDone(){print('done');}

  pauseStream(){_streamSubsctiption.pause();}
  cancelStream(){_streamSubsctiption.cancel();}
  resumeStream(){_streamSubsctiption.resume();}

  @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,
      ),
      body: Center(
        child: Column(
          children: <Widget>[
            RaisedButton(
              child: Text('AddDataToStream'),
              onPressed: _addDataToStream,
            ),
            RaisedButton(
              child: Text('pause'),
              onPressed: pauseStream,
            ),
            RaisedButton(
              child: Text('cancel'),
              onPressed: cancelStream,
            ),
            RaisedButton(
              child: Text('resume'),
              onPressed: resumeStream,
            ),
          ],
        ),
      )
    );
  }
}
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