[[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];
 [[NSNotificationCenter defaultCenter] addObserver:self
                                          selector:@selector(orientationChanged:)
                                              name:UIApplicationDidChangeStatusBarFrameNotification
                                                   object:nil];

[[NSNotificationCenter defaultCenter] removeObserver:self];
[[UIDevice currentDevice] endGeneratingDeviceOrientationNotifications];

- (void)orientationChanged:(NSNotification *)notification
{
    ...
}