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

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

class MyApp extends StatelessWidget {

  final StreamController _streamController = StreamController<int>();

  int count = 10;



  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("短信倒计时"),
        ),
        body: Center(
          child: StreamBuilder<int>(
              stream: _streamController.stream,
              initialData: 0,
              builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
                return RaisedButton(
                  onPressed: () async {
                    if (snapshot.data == 0) {
                      _startTimer();
                    }
                  },

                  child: Text(
                    snapshot.data == 0 ? "获取验证码" : '${snapshot
                        .data} 秒后重发',
                    style: snapshot.data == 0
                        ? TextStyle(color: Colors.blue, fontSize: 14)
                        : TextStyle(color: Colors.grey, fontSize: 14),
                  ),
                );
              }
          ),
        ),
      )
    );
  }


  void _startTimer() {
    count = 60;
    _timer = Timer.periodic(Duration(seconds: 1), (timer) {
      if (count <= 0) {
        _cancelTimer();
        return;
      }
      _streamController.sink.add(--count);
    });
  }
  /// 取消倒计时的计时器。
  void _cancelTimer() {
    // 计时器（`Timer`）组件的取消（`cancel`）方法，取消计时器。
    _timer?.cancel();
  }
  void dispose() {
    // TODO: implement dispose
    //关掉不需要的Stream;
    _streamController.close();
    super.dispose();
  }

}