Btukfyl

In UWP I'm trying to create a simple background task on demand. So when I click a button, I want a background task to kick off and process some files in the background.

Below is what my basic Task code is:

public class BackgroundSyncService

{

    private ApplicationTrigger trigger = new ApplicationTrigger();



    public async Task Start()

    {

        if (IsRegistered())

            Deregister();



        BackgroundExecutionManager.RemoveAccess();



        // does this prompt everytime?

        await BackgroundExecutionManager.RequestAccessAsync();



        var builder = new BackgroundTaskBuilder();



        builder.Name = "BackgroundTask";

        builder.TaskEntryPoint = typeof(BackgroundTask).FullName;



        builder.SetTrigger(trigger);

        BackgroundTaskRegistration task = builder.Register();



        task.Completed += Task_Completed;



        var result = await trigger.RequestAsync();

    }



    private void Task_Completed(BackgroundTaskRegistration sender, BackgroundTaskCompletedEventArgs args)

    {

        // alert UI

    }



    public void Stop()

    {

        Deregister();

    }



    private void Deregister()

    {

        var taskName = "BackgroundTask";



        foreach (var task in BackgroundTaskRegistration.AllTasks)

            if (task.Value.Name == taskName)

                task.Value.Unregister(true);

    }



    private bool IsRegistered()

    {

        var taskName = "BackgroundTask";



        foreach (var task in BackgroundTaskRegistration.AllTasks)

            if (task.Value.Name == taskName)

                return true;



        return false;

    }

}

When the code hits builder.Register() it throws the following exception:

System.Exception: 'Cannot create a file when that file already exists.
(Exception from HRESULT: 0x800700B7)'

Not sure what I'm doing wrong here or what this error means in context of a Background Task?

For your issue, it is because you have a file with the specified name already exists in the current folder when you create the file. You can try to specify the NameCollisionOption when you create the file.

var file = await ApplicationData.Current.LocalFolder.

    CreateFileAsync("MyFile", CreationCollisionOption.ReplaceExisting);

As your code in your example project, you have used the ApplicationData.LocalSettings, when you add the setting key, you should check whether the key is existing.

var settings = Windows.Storage.ApplicationData.Current.LocalSettings;

if (!settings.Values.ContainsKey("BackgroundTask"))

{

    settings.Values.Add("BackgroundTask", "Hello from UWP");

}

Or you can use the ApplicationData.LocalSettings as following to use the key and change its value,

var settings = Windows.Storage.ApplicationData.Current.LocalSettings;

settings.Values["BackgroundTask"] = "Hello from UWP";

You can also look into the Store and retrieve settings and other app data topic.