Rotate a UIImageView in an iOS app that does not support rotation

Question

I have an application that is hard coded to support only 1 orientation, portrait. Portrait is set via project settings.

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{   
      return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

Within this view controller there are several views, buttons, labels and other standard iOS controls. For all controls within this view controller, the desired behavior is that when a user rotates the iOS device, nothing within the application rotates.

However, below all of the aforementioned views, acting as a "Background" is a UIImageView embedded within a UIScrollView. This is the bottom most view. At anytime, a user is able to change this background via a button that launches a photo picker. The UIImageView is embedded within the UIScrollView because desired behavior is to allow pinch to zoom on the background image.

Although the application does not support rotation, I would like for the content of the ImageView to always be oriented correctly when loaded.

For Example - keeping in mind that the only supported orientation is UIInterfaceOrientationPortrait, a user launches the application, rotates the iOS device to a LandScape position. While in portrait user selects new background image. The intended behavior would be for the image selected to be oriented & aspect correct based on the current orientation.

Essentially, I'm looking for that background image to always have a "Gravity" towards earth upon being selected. If after the user selects a new image then they rotate the iOS Device, the background image does not rotate. Only upon initially selecting the image would it orientate correctly.

I'm able to rotate the image using CGAffineTransformMakeRotation, however zooming in via pinch exhibits undesirable behavior as the pixels within the image itself don't really change orientation.

I'm thinking I might need to actually create a new image when the user selects an image, something along the lines of ...

UIImage * RightLandscapeImage = [[UIImage alloc] initWithCGImage: userSelectedImage.CGImage
                                                         scale: 1.0
                                                   orientation: UIImageOrientationRight];

I don't see any simple solution for this issue. Possibly I am overlooking something easy?

FOLLOW UP this is the code that seems to be required. Taking into account the current orientation, and the startup orientation.

UIImage * newImage;
if( startUpOrientation == UIInterfaceOrientationLandscapeRight )
{
    switch (currentOrientation) {
        case UIInterfaceOrientationLandscapeLeft:
          newImage = [[UIImage alloc] initWithCGImage: bgImage.CGImage
                                                                 scale: 1.0
                                                           orientation: UIImageOrientationDownMirrored];

             [self.backgroundImageView setImage:newImage];
            break;
        case UIInterfaceOrientationLandscapeRight:
             [self.backgroundImageView setImage:bgImage];
            break;
        case UIInterfaceOrientationPortraitUpsideDown:
            newImage = [[UIImage alloc] initWithCGImage: bgImage.CGImage
                                                  scale: 1.0
                                            orientation: UIImageOrientationRight];

            [self.backgroundImageView setImage:newImage];

            break;
        default:
            newImage = [[UIImage alloc] initWithCGImage: bgImage.CGImage
                                                  scale: 1.0
                                            orientation: UIImageOrientationLeft];
            [self.backgroundImageView setImage:newImage];
            break;
    }
 }

Answer 1

You can apply transform to any view you want to rotate in willRotateToInterfaceOrientation

You can try this code:

- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration
    {
        switch (toInterfaceOrientation) {
            case UIInterfaceOrientationLandscapeLeft:
                yourview.transform = CGAffineTransformMakeRotation(M_PI_2); // 90 degress
                break;
            case UIInterfaceOrientationLandscapeRight:
                yourview.transform = CGAffineTransformMakeRotation(M_PI + M_PI_2); // 270 degrees
                break;
            case UIInterfaceOrientationPortraitUpsideDown:
                yourview.transform = CGAffineTransformMakeRotation(M_PI); // 180 degrees
                break;
            default:
                yourview.transform = CGAffineTransformMakeRotation(0.0);
                break;
        }
    }