I'm catching up on all the great geo changes that have gone into Collect recently. Previously, offline raster tiles only worked when the mapping engine selected was OpenStreetMaps. Now it's possible to load them with the Google Maps engine which is great. However, the behavior of the two is different. With OSM, all the user sees are the offline tiles (I believe the offline tiles are rendered on top of the online ones but the online ones don't show through). With Google Maps, the offline tiles are displayed on top of the online ones with the online ones also showing.
@zestyping, is this discrepancy due to differing capabilities offered by the two SDKs? Would it be possible for both modes to be supported by both engines?
Or is it perhaps dependent on the nature of the tiles? I used the PNG mbtiles file from here and got the following: