iOS系统通知NSNotificationName

• 当程序被推送到后台时

UIApplicationDidEnterBackgroundNotification

• 当程序从后台将要重新回到前台时

UIApplicationWillEnterForegroundNotification

• 当程序完成载入后通知

UIApplicationDidFinishLaunchingNotification

• 应用程序转为激活状态时

UIApplicationDidBecomeActiveNotification

• 用户按下主屏幕按钮调用通知，并未进入后台状态

UIApplicationWillResignActiveNotification

• 内存较低时通知

UIApplicationDidReceiveMemoryWarningNotification

• 当程序将要退出时通知

UIApplicationWillTerminateNotification

• 当系统时间发生改变时通知

UIApplicationSignificantTimeChangeNotification

• 当StatusBar框方向将要变化时通知

UIApplicationWillChangeStatusBarOrientationNotification
// userInfo contains NSNumber with new orientation

• 当StatusBar框方向改变时通知

UIApplicationDidChangeStatusBarOrientationNotification
// userInfo contains NSNumber with old orientation

UIApplicationStatusBarOrientationUserInfoKey
// userInfo dictionary key for status bar orientation

• 当StatusBar框方向将要改变时通知

UIApplicationWillChangeStatusBarFrameNotification 
// userInfo contains NSValue with new frame

• 系统状态栏已经发生变化通知

UIApplicationDidChangeStatusBarFrameNotification
// userInfo contains NSValue with old frame

UIApplicationStatusBarFrameUserInfoKey
// userInfo dictionary key for status bar frame

• 后台下载状态发生改变时通知（iOS7.0以后可用）

UIApplicationBackgroundRefreshStatusDidChangeNotification

• 受保护的文件当前变为不可用时通知

UIApplicationProtectedDataWillBecomeUnavailable

• 受保护的文件当前变为可用时通知

UIApplicationProtectedDataDidBecomeAvailable

• 截屏通知（iOS7.0以后可用）

UIApplicationUserDidTakeScreenshotNotification