UWP in-process background task when app is closed

Question

Does the in-process background task, defined via the OnBackgroundActivated method, run even if the main application is closed or suspended or must I implement an out-of-process background task?

The documentation is not clear on this.

• Support your app with background tasks
• Create and register an out-of-process background task
• Create and register an in-process background task

I've written out-of-process background tasks before and they run even when the app is not. However, it seems to me that an in-process background task won't run unless the app is active. I've used a deferral, as suggested in the documentation, to avoid the task being closed, and I've set the oneShot to false when registering the task. The task takes no longer than 10 seconds. The task is registered and can be run manually from Visual Studio, but doesn't seem to run automatically, if the app is closed.

protected async override void OnBackgroundActivated(BackgroundActivatedEventArgs args)
{
    base.OnBackgroundActivated(args);
    IBackgroundTaskInstance taskInstance = args.TaskInstance;
    BackgroundTaskDeferral deferral = taskInstance.GetDeferral();
    await RunBackgroundWork();
    deferral.Complete();
}

In summary, if you need to create a background task that should run even if the main app is not open, can this be done with an in-process background task, or must an out-of-process background task be used?

Answer 1

Turns out, contrary to the answer the condescending Microsoft employee provided, that the background task will run if the app is closed, even if it is implemented as an in-process background task.

If the background task is implemented as an in-process task, then the OnBackgroundActivated method will be used as the entry point, in case the app is not running. Otherwise, the method will be called while the app is running.

The reason why there were problems with the background task starting was that I used a condition (namely the SystemConditionType.UserPresent) on the task. This behaves very unpredictably. However, I tested (by waiting for several calls) both the in-process and out-of-process approach and the task gets run in both cases, even if the app is closed.

If a task deferral is used, the background task should not be terminated even if the user closes the app.

In conclusion, at the time of writing this post (October 17th, 2020) the documentation does not clearly explain this behavior and the aforementioned condescending misinterpretation by, ironically enough, Microsoft's own employee only proves that point.

Answer 2

Does the in-process background task, defined via the OnBackgroundActivated method, run even if the main application is closed or suspended

Derive from the definition of in-process background task In-process: the app and its background process run in the same process. So if your app is close the in-process background task will be terminated.

In summary, if you need to create a background task that should run even if the main app is not open, can this be done with an in-process background task, or must an out-of-process background task be used?

Be aware that background activity can be terminated even when running inside the app's foreground process if it runs past execution time limits. For some purposes the resiliency of separating work into a background task that runs in a separate process is still useful. Keeping background work as a task separate from the foreground application may be the best option for work that does not require communication with the foreground application.

For your scenario, out-of-process background task is better choice.