[[NSNotificationCenter defaultCenter] addObserver:self                                         selector:@selector(appHasGoneInForeground:)                                      name:UIApplicationWillEnterForegroundNotification                                           object:nil];  //别忘了删除监听[[NSNotificationCenter defaultCenter] removeObserver:self];

UIApplicationDidEnterBackgroundNotification  //进入后台UIApplicationWillEnterForegroundNotification //回到程序