How To Handle UIImage on device rotation

I have a UIScrollView with a UIImage inside. The following code initializes the image properly (it's width is the same as the width of the scrollView):

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
    [super viewDidLoad];

    ...

    imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"map1.jpg"]];
    imageView.userInteractionEnabled = YES;
    imageView.autoresizingMask = ( UIViewAutoresizingFlexibleWidth );
    [imageScrollView addSubview:imageView];

    imageScrollView.contentSize = [imageView frame].size;

    ...

    // calculate minimum scal开发者_如何学运维e to perfectly fit image width, and begin at that scale
    float minimumScale = [imageScrollView frame].size.width  / [imageView frame].size.width;
    //imageScrollView.maximumZoomScale = 1.0;
    imageScrollView.minimumZoomScale = minimumScale;
    imageScrollView.zoomScale = minimumScale;
}

What I want to do is to set the size to perfectly fit (like above) when the device rotates. Here's what I've tried to do:

- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation {
  float newScale = [imageScrollView frame].size.width  / [imageView frame].size.width;
  imageScrollView.zoomScale = newScale;
}

For some reasons this doesn't work at all. The only way that I was able to make it work was to initialize another UIImage and do all the initialization process again, which doesn't feel right to me.

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Probably you should also change .contentSize of scroll view.