abstract fun onLoadRequested(initial: Boolean): Unit
Callback method when the user has viewed all of the available artwork. This should be used as a cue to load more artwork so that the user has a constant stream of new artwork.
Muzei will always prefer to show unseen artwork, but will automatically cycle through all of the available artwork if no new artwork is found (i.e., if you don't load new artwork after receiving this callback).
initial - true when there is no artwork available, such as is the case when this is
the initial load of this MuzeiArtProvider.