WriteableBitmap inside Windows 10 IBackgroundTask

I am trying to crop an image from a Run method from Windows 10 app (UWP) IBackgroundTask. To achive that I'm using the WriteableBitmapEx but at the moment that I try to instantiate a new object, I got the exception:

The application called an interface that was marshalled for a different thread. (Exception from HRESULT: 0x8001010E (RPC_E_WRONG_THREAD))

I have tried to use some Dispatchers but other exception ocurred. Any idea?

WriteableBitmap is a UI object, and requires UI thread, which background task lacks of.

Depending on your needs, you can either use different API to work with images (check this topic for BitmapEncoder) or derive your background task from XamlRenderingBackgroundTask, which will call its OnRun method in UI thread. Although keep in mind, that it's recommended to use C++ in XamlRenderingBackgroundTask due to memory limitations.