Get value of Widget in appbar

Question

I need to get value of my widget countdown to each second for control if the time it's not finish. I don't find how I can do... How i can get the value of the widget? How i can get the value to each second? For the integration in other widget, I think i can do it.

My countdown widget:

class _CountdownState extends State<Countdown> {

  Countdown c = new Countdown();
  Timer _timer;
  int seconds = 0;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Text(constructTime(seconds), style: TextStyle(fontSize: 18, color: Colors.white, fontStyle: FontStyle.italic),),
    );
  }

  String constructTime(int seconds) {
    if(seconds == 0){
      return "";
    }
    int hour = seconds ~/ 3600;
    int minute = seconds % 3600 ~/ 60;
    int second = seconds % 60;
    return formatTime(hour) + ":" + formatTime(minute) + ":" + formatTime(second);
  }

  String formatTime(int timeNum) {
    return timeNum < 10 ? "0" + timeNum.toString() : timeNum.toString();
  }

  @override
  initState(){
    super.initState();
    getDate();
    startTimer();
  }

  void getDate() async{
    var now = DateTime.now();
    /*String creationDate = await Poll().getCreationDateToSF();
    DateTime creationDateTime = DateTime.parse(creationDate);*/
    var creationDateTime = DateTime.now().add(new Duration(seconds: 15));
    seconds = creationDateTime.difference(now).inSeconds;
  }

  void startTimer() {
    const period = const Duration(seconds: 1);
    _timer = Timer.periodic(period, (timer) {
      setState(() {
        seconds--;
      });
      if (seconds == 0) {
        cancelTimer();
      }
    });
  }

  void cancelTimer() {
    if (_timer != null) {
      _timer.cancel();
      _timer = null;
      c.onCountDownComplete();
    }
  }

  @override
  void dispose() {
    super.dispose();
    cancelTimer();
  }
}

I added the method for print the message in other page and i call the Countdown(onCountDownComplete: onCountDown) in my Poll State Class

I want to control in other page, when the result of my countdown is finish, i stop my app.

EDITED:

E/flutter ( 5306): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The method 'call' was called on null.
E/flutter ( 5306): Receiver: null
E/flutter ( 5306): Tried calling: call()
E/flutter ( 5306): #0      Object.noSuchMethod  (dart:core-patch/object_patch.dart:51:5)
E/flutter ( 5306): #1      _CountdownState.cancelTimer 
package:blackbox/…/widgets/countDown.dart:75
E/flutter ( 5306): #2      _CountdownState.startTimer.<anonymous closure> 
package:blackbox/…/widgets/countDown.dart:66
E/flutter ( 5306): #3      _rootRunUnary  (dart:async/zone.dart:1132:38)
E/flutter ( 5306): #4      _CustomZone.runUnary  (dart:async/zone.dart:1029:19)
E/flutter ( 5306): #5      _CustomZone.runUnaryGuarded  (dart:async/zone.dart:931:7)
E/flutter ( 5306): #6      _CustomZone.bindUnaryCallbackGuarded.<anonymous closure>  (dart:async/zone.dart:968:26)
E/flutter ( 5306): #7      _rootRunUnary  (dart:async/zone.dart:1136:13)
E/flutter ( 5306): #8      _CustomZone.runUnary  (dart:async/zone.dart:1029:19)
E/flutter ( 5306): #9      _CustomZone.bindUnaryCallback.<anonymous closure>  (dart:async/zone.dart:952:26)
E/flutter ( 5306): #10     _Timer._runTimers  (dart:isolate-patch/timer_impl.dart:382:19)
E/flutter ( 5306): #11     _Timer._handleMessage  (dart:isolate-patch/timer_impl.dart:416:5)
E/flutter ( 5306): #12     _RawReceivePortImpl._handleMessage  (dart:isolate-patch/isolate_patch.dart:172:12)

Answer 1

try this code:

Change your Countdown class like this:

class Countdown extends StatefulWidget {
  final Function onCountDownComplete;
  Countdown({this.onCountDownComplete});
  @override
  _CountdownState createState() => _CountdownState();
}

class _CountdownState extends State<Countdown> {
  Timer _timer;
  int seconds = 0;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Text(
        constructTime(seconds),
        style: TextStyle(
            fontSize: 18, color: Colors.white, fontStyle: FontStyle.italic),
      ),
    );
  }

  String constructTime(int seconds) {
    int hour = seconds ~/ 3600;
    int minute = seconds % 3600 ~/ 60;
    int second = seconds % 60;
    return formatTime(hour) +
        ":" +
        formatTime(minute) +
        ":" +
        formatTime(second);
  }

  String formatTime(int timeNum) {
    return timeNum < 10 ? "0" + timeNum.toString() : timeNum.toString();
  }

  @override
  initState() {
    getDate();
    //startTimer();
    super.initState();
  }

  void getDate() async {
    var now = DateTime.now();
    String creationDate = '12:20:11';
    DateTime creationDateTime = DateTime.parse(creationDate);
    seconds = creationDateTime.difference(now).inSeconds;
    startTimer();
  }

  void startTimer() {
    const period = const Duration(seconds: 1);
    _timer = Timer.periodic(period, (timer) {
      setState(() {
        seconds--;
      });
      if (seconds == 0) {
        cancelTimer();
      }
    });
  }

  void cancelTimer() {
    if (_timer != null) {
      _timer.cancel();
      _timer = null;
      widget.onCountDownComplete();
    }
  }

  @override
  void dispose() {
    super.dispose();
    cancelTimer();
  }
}

For use Countdown:

 void onCountDown() {
    print('Complete Count down');
  }


Countdown(onCountDownComplete: onCountDown)