By background, I mean none of the application\'s activities are currently visible to the user?
It might be too late to answer but if somebody comes visiting then here is the solution I suggest, The reason(s) an app wants to know it's state of being in background or coming to foreground can be many, a few are, 1. To show toasts and notifications when the user is in BG. 2.To perform some tasks for the first time user comes from BG, like a poll, redraw etc.
The solution by Idolon and others takes care of the first part, but does not for the second. If there are multiple activities in your app, and the user is switching between them, then by the time you are in second activity, the visible flag will be false. So it cannot be used deterministically.
I did something what was suggested by CommonsWare, "If the Service determines that there are no activities visible, and it remains that way for some amount of time, stop the data transfer at the next logical stopping point."
The line in bold is important and this can be used to achieve second item. So what I do is once I get the onActivityPaused() , don not change the visible to false directly, instead have a timer of 3 seconds (that is the max that the next activity should be launched), and if there is not onActivityResumed() call in the next 3 seconds, change visible to false. Similarly in onActivityResumed() if there is a timer then I cancel it. To sum up,the visible becomes isAppInBackground.
Sorry cannot copy-paste the code...