Oh, I should have been more explicit. I meant android libraries that provide their own UI for user interaction. Think of a third-party service that does passport validation for you or something like that. So, user goes through a complex flow, maybe takes some pictures, etc. and all of this is coming from an sdk, that you're usually provided with. It's a non trivial task to provide an API that will fit nice on the client side (how to handle onActivityResult?) and I was looking for good practicies.