android 如何判断程序是否在前台运行

private boolean isTopActivity(){
		List<RunningTaskInfo>  tasksInfo = activityManager.getRunningTasks(1);
		if(tasksInfo.size() > 0){
			//应用程序位于堆栈的顶层
			if(packageName.equals(tasksInfo.get(0).topActivity.getPackageName())){
				return true;
			}
		}
		return false;
	}