How to track activity visibilty considering dialogs and system windows?

Question

A task: I should track visibility of whole Android application and generate events when it goes to background or foreground. First part of the task is completed: I have special global counter which I increment in Activity onStart() and decrement in Activity onStop(), when this counter downs to zero then my application has gone to background.

Second part of the task is tricker. I know about strange behavior of onResume() and advice to use onWindowFocusChanged(boolean). I looked into documentation of onWindowFocusChanged(boolean) and noticed such thing:

As a general rule, however, a resumed activity will have window focus... unless it has displayed other dialogs or popups that take input focus, in which case the activity itself will not have focus when the other windows have it. Likewise, the system may display system-level windows (such as the status bar notification panel or a system alert) which will temporarily take window input focus without pausing the foreground activity.

Is any way to check out: whose window is shown over resumed activity from my app? Is it my dialog or keyguard? Is any way to catch event: all but mine windows over resumed activities are removed?

Answer 1

Your counter based approach is plain wrong. One reason: onStop() is not guaranted to execute.

I would assume that your notion of "background" and "foreground" should be the same as that of Android. However, when I read what you have done so far, it seems as if you have a different idea of what "background" and "foreground" mean, than Android has.

From there:

• If you have an idea of what background and foreground mean which differs from Android, you're not doing yourself a favour and probably follow a misguided path, so recosnider adjusting the meaning of foreground and background.
• Once you have the same idea as Android about background and foreground, the question is, why do you have to generate events when Android already does that. If you have to send events to a service or such, then it will be simple by listening for Activity lifecycle events and firing corresponding events for your Service.

Regarding onWindowFocusChanged: Yes, of course the notification panel can hide your App temporarily; have you used an Android device yet? The big question here is whether you would consider your App in the background then, because Android considers your App to be in the background if the notification panel is being shown.

Update: I just re-read your Q's title. Unfortunately, you're not stating what you really want/need to do, because visibility can mean a lot of things. E.g. do you consider your app to be visible if a semi transparent notification panel is laid out on top of it, or not? But the bottom line remains the same: It would be easiest if you align what you want with what Android does offer. ;)

Update 2: If you really need to know whether your Activity has been moved to the background by a popup of your own activity or by yourself, this answer here should give you the information you need.