Update background image of a view based on device orientation

UIImageView+DeviceOrientation.m

/* 
   Add this in a view
*/

- (void)viewWillAppear:(BOOL)animated {    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(orientationChanged:) name:UIDeviceOrientationDidChangeNotification object:nil];
}

// Update the background image if the device is an iPad and its orientation changed
- (void)orientationChanged:(NSNotification *)notification {
    if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
        if (UIDeviceOrientationIsLandscape([UIDevice currentDevice].orientation)) {
            UIImage* img = [UIImage imageNamed:@"background-landscape~ipad.png"];
            [self.ipadBackgroundImageView setImage:img];
            self.ipadBackgroundImageView.transform = CGAffineTransformMakeRotation(M_PI/2);
            NSLog(@"Device orientation changed to Landscape");
        } else if (UIDeviceOrientationIsPortrait([UIDevice currentDevice].orientation)) {
            [self.ipadBackgroundImageView setImage:[UIImage imageNamed:@"background-portrait~ipad.png"]];
            self.ipadBackgroundImageView.transform = CGAffineTransformMakeRotation(0.0);
            NSLog(@"Device orientation changed to Portrait");
        }
    }
}

- (void)viewDidDisappear:(BOOL)animated {
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIDeviceOrientationDidChangeNotification object:nil];
}

/*

In application delegate's didFinishLaunchingWithOptions, add this - 

    // Start generating device orientation change notifications
    [[UIDevice currentDevice] beginGeneratingDeviceOrientationNotifications];


*/