Background tasks with Workmanager plugin don't work in flutter

Question

I'm trying to trigger some background tasks with a button and am finding the workmanager plugin for flutter to be very temperamental. It works occasionally but this is few and far between.

I'm testing it with this basic app:

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

const task1 = "simpleTask";

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  Workmanager.initialize(
      callbackDispatcher, 
      isInDebugMode: true, 
  ); 
  //Workmanager.registerPeriodicTask("1", task1, initialDelay: Duration(seconds: 10), frequency: Duration(minutes: 15));
  //Workmanager.registerOneOffTask("1", task1, initialDelay: Duration(seconds: 5));
  runApp(MaterialApp(
  home: Scaffold(
    body: Container(
      color: Colors.blueAccent[400],
      child: Center(
        child: RaisedButton(
          child: Text("create notification in five seconds"),
          onPressed: () {
            Workmanager.registerOneOffTask("1", task1, initialDelay: Duration(seconds: 5));
          },
        ),
      ),
    ),
  ),
));}


void callbackDispatcher() {
  Workmanager.executeTask((task, inputData) {
    print("it's doing the task");
    switch (task) {
      case task1:
        print(task1);
        break;
      case Workmanager.iOSBackgroundTask:
        print("iOS background fetch delegate ran");
        break;
    }
    return Future.value(true);
});
}

I'm trying to trigger a background task from a button because it wasn't working as I had it before where the two lines are commented out. I have also never had the Workmanager.registerPeriodicTask work. This could be that the initial delay doesn't set off the first task at the end but instead starts the 15-minute timer until the first one but it's a massive pain to test given that I have to wait for a minimum of 15 minutes.

Is there a command that I'm missing or a necessary await that I'm missing or something?

Edit: I've just tested it on an Android emulator from AndroidStudio and the notifications all work exactly as they should for both one-off and periodic tasks so I think it is something to do with the phone maybe. Not really sure what to do about it though.

Answer 1

I fixed this error by adding @pragma(‘vm:entry-point’) on a top line of headless (top-level) callbackDispatcher function. So like this:

@pragma('vm:entry-point')
void callbackDispatcher() {
  Workmanager().executeTask((task, inputData) async {
    print("Native called background task: $task");
    ....
    return Future.value(true);
  });
}

Source: https://learnpainless.com/flutter/flutter-workmanager-not-working-in-release-mode-working-in-debug-mode/

Answer 2

I've tried the code you've provided and the only issue I've encountered is initialize(), registerOneOffTask(), and executeTask() can't be accessed with a static call from Workmanager. Other than that the code works fine.

As mentioned in this doc, Android background tasks might be spotty since Android decides when is the best time to run. There is no guaranteed way to enforce a run of a job even in debug mode.