flutterdarttimerpush-notificationbackground-process

Flutter: run code like a timer when app is running in background


I have a simple timer which works fine when the app is running in foreground. I can listen to the stream and update the UI. However when the app is in the background it will not continue counting. How can I continue counting when the app is running in the background?

This is my code for the timer:

class SetTimer {
  int _seconds = 0;
  final _streamController = StreamController<int>.broadcast();
  Timer? _timer;

  // Getters
  Stream<int> get stream => _streamController.stream;

  // Setters
  void start() {
    _timer = Timer.periodic(const Duration(seconds: 1), (_) {
      _seconds++;
      _updateSeconds();
    });
  }

  void _updateSeconds() {
    // stop counting after one hour
    if (_seconds < 3600) {
      _streamController.sink.add(_seconds);
    }
  }
}

Solution

  • Try the below code -
    I tested it & found it will count the number in the background & there is no problem.
    I added a screen record video here, it will help you to understand.

    import 'dart:async';
    import 'package:flutter/material.dart';
    
    void main() {
      runApp(const MyApp());
    }
    
    class MyApp extends StatelessWidget {
      const MyApp({Key? key}) : super(key: key);
    
      @override
      Widget build(BuildContext context) {
        return const MaterialApp(
          title: 'Flutter Demo',
          home: MyTest(),
        );
      }
    }
    
    class MyTest extends StatefulWidget {
      const MyTest({Key? key}) : super(key: key);
    
      @override
      State<MyTest> createState() => _MyTestState();
    }
    
    class _MyTestState extends State<MyTest> {
      final SetTimer _setTimer = SetTimer();
    
      @override
      void initState() {
        _setTimer.start();
        super.initState();
      }
    
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          body: StreamBuilder<int>(
            stream: _setTimer.stream,
            builder: (
                BuildContext context,
                AsyncSnapshot<int> snapshot,
                ) {
              if (snapshot.connectionState == ConnectionState.waiting) {
                return CircularProgressIndicator();
              } else if (snapshot.connectionState == ConnectionState.active
                  || snapshot.connectionState == ConnectionState.done) {
                if (snapshot.hasError) {
                  return const Text('Error');
                } else if (snapshot.hasData) {
                  return Center(
                    child: Text(
                        snapshot.data.toString(),
                        style: const TextStyle(color: Colors.red, fontSize: 40)
                    ),
                  );
                } else {
                  return const Text('Empty data');
                }
              } else {
                return Text('State: ${snapshot.connectionState}');
              }
            },
          ),
        );
      }
    }
    
    class SetTimer {
      int _seconds = 0;
      final _streamController = StreamController<int>.broadcast();
      Timer? _timer;
    
      // Getters
      Stream<int> get stream => _streamController.stream;
    
      // Setters
      void start() {
        _timer = Timer.periodic(const Duration(seconds: 1), (_) {
          _seconds++;
          _updateSeconds();
        });
      }
    
      void _updateSeconds() {
        // stop counting after one hour
        if (_seconds < 3600) {
          _streamController.sink.add(_seconds);
        }
      }
    }