[iOS] 회전 이벤트 받기 (Detecting rotation to landscape manually)

1) 통지 메세지 등록:
[[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(detectOrientation) name:@"UIDeviceOrientationDidChangeNotification" object:nil];  
2) 통지 이벤트에 대한 처리 함수:
-(void) detectOrientation {
    if (([[UIDevice currentDevice] orientation] == UIDeviceOrientationLandscapeLeft) || 
        ([[UIDevice currentDevice] orientation] == UIDeviceOrientationLandscapeRight)) {
        [self doLandscapeThings];
    } else if ([[UIDevice currentDevice] orientation] == UIDeviceOrientationPortrait) {
        [self doPortraitThings];
    }   
}