Send notifications only when activity is in background

I need a way to determine whether ativity active or 开发者_运维问答in the background. I have a service which notifies user, but I want to do it only when activity is inactive. I might use global variables, set them in onStop() for example, but is there any other way?

Have you try to do it with ActivityManager#getRunningAppProcesses() took the idea directly from How to determine if one of my activities is in foreground