So HoloLens is stupid in that it only recognizes one FilePicker at a time (no matter how many may be installed). I don't believe the developers are going to try making multiple filepickers work.
So, I'm trying to figure out my own filepicker in an attempt to be a proxy-select for other filepickers.
In essence, I want to make a filepicker chooser that appears as a typical filepicker (if that makes sense).
Trouble is, it doesn't appear possible to get a list of pickers installed!
Am I experiencing a pipe dream, or is there a way to invoke a picker from a list of pickers?
For the moment this is a pipe dream, but I sure hope they fix this. Per the Windows Holographic FAQ:
Note: HoloLens will always use the first app you've installed to handle file storage and this can't be changed. That means if you install Box and then OneDrive, all apps will use the Box file picker app.
来源：https://stackoverflow.com/questions/38781701/filepicker-for-hololens-list-available-filepickers