How to know if my android app is visible?

I have a timer that start a notification when it ends. But I would like to fire a notification using notificationManager only if the app is not currently visible, and to show an alertDialog if the timer ends while the app is in foreground.

I've already tried with this :

ActivityManager actMngr = (ActivityManager) ValeoMobileApplication.getContext().getSystemService(Activity.ACTIVITY_SERVICE);
List<RunningAppProcessInfo> runningAppProcesses = actMngr.getRunningAppProcesses();
Tools.log("TimerBroadcastReceiver", "onReceive", "All running processes are listed below :");
for (RunningAppProcessInfo pi : runningAppProcesses) {
    //Check pi.processName and do your stuff
    //also check pi importance - check if process is in foreground or background
    Tools.log("TimerBroadcastReceiver", "onReceive", pi.processName + " importance = "+pi.importance);
    if(pi.processName.equalsIgnoreCase("MY_APP_PROCESS_NAME")){
        if (pi.importance == RunningAppProcessInfo.IMPORTANCE_FOREGROUND) {
            isApplicationInForeground = true;
        }
    }
}

But it seems that it doesn't matter if the app is foreground or not. How can I do this?