Why is my WinRT app closing when trying to debug my background task?

Question

I am trying to experiment with downloading files on a regular basis with background tasks for windows store applications, and am having trouble.

I followed the sample at https://msdn.microsoft.com/en-us/library/windows/apps/xaml/hh977055.aspx, and even downloaded/ran it and everything worked perfectly (including being able to step into the timer background task).

So with that I created my own background task in a brand new Windows namespace

Win8BackgroundTest
{
    public class TestBackgroundTask
    {
        public async void Run(IBackgroundTaskInstance taskInstance)
        {
            var deferral = taskInstance.GetDeferral();

            var uri = new Uri("http://download.blender.org/peach/bigbuckbunny_movies/big_buck_bunny_480p_h264.mov");
            var folder = ApplicationData.Current.LocalFolder;
            var downloadFile = await folder.CreateFileAsync(uri.Segments.Last(), CreationCollisionOption.GenerateUniqueName);
            var dataFile = await folder.CreateFileAsync("downloadData", CreationCollisionOption.GenerateUniqueName);
            var downloader = new BackgroundDownloader();
            var operation = downloader.CreateDownload(uri, downloadFile);

            await FileIO.WriteTextAsync(dataFile, "Success at " + DateTime.Now);

            deferral.Complete();
        }

        public static async void RegisterTask()
        {
            const string taskName = "TestBackgroundTask";

            try
            {
                var status = await BackgroundExecutionManager.RequestAccessAsync();
                if (status == BackgroundAccessStatus.Denied)
                {
                    return;
                }
            }
            catch
            {
                // already accepted
            }

            var tasks = BackgroundTaskRegistration.AllTasks
                .Where(x => x.Value.Name == taskName)
                .ToArray();

            if (tasks.Any())
            {
                return;
            }

            var builder = new BackgroundTaskBuilder
            {
                Name = taskName,
                TaskEntryPoint = "Win8BackgroundTest.TestBackgroundTask",
            };

            builder.SetTrigger(new TimeTrigger(60, false));

            var registeredTask = builder.Register();
        }
    }
}

I set up the application's manifest with a Background Tasks declaration, checking the Timer properties checkbox, and set the EntryPoint to Win8BackgroundTest.TestBackgroundTask.

I then added the following at the end of my App.xaml.cs's OnLaunched() method:

        TestBackgroundTask.RegisterTask();

Stepping through seems to have task registration work successfully with no exceptions. I then go back to visual studio, added a breakpoint to the first line in my task's Run() method, I then go to the debug locations toolbar, click the down arrow and select TestBackgroundTask. A few seconds later visual studio exits (as does my app).

Does anyone see what I am doing wrong that is causing background tasks to fail?

Answer 1

So after much frustration and a lot of trial and error the issue was a combination of both of the comments.

So first of all, it appears like you cannot have a background task in the same project as the rest of your windows store application. It must be in it's own windows runtime component project.

Finally, there are times where it just doesn't work and for whatever reason deleting the bin and obj folders fix it.