Read MediaPlayer caching state

Hi

I have an ImageMediaSource holding a lot images. When i open them in a MediaPlayer i want to wait until all images are pre cached. In other words i do like to get notified about the pre caching state. I tried is Buffering and is Preparing. They always deliver False.
Are there other methods to get the caching state?

I have already asked a question about Image Media Source. But there are no answers specifically to this topic. Hopefully there is someone here who knows about it.
Pre cache Image Media Source

Thanks in advance