android 如何判断应用是否在前台运行

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;
}