I am implementing an app locker for Android where the user can block apps and other users can not access these apps without an access key. Can I show ads on app lock screen?
Well, this is a very bad idea to do so. If you are still looking to implement ad stuff, you can do the stuff in call back on adding right pin or lock. Once user entered the right lock (pin code OR biometric) you will verify in some how if user entered credentials valid then you should show the ad.