iPhone UIImageView in UIScrollView not zooming to center

I have a UIImageView inside a UIScrollView so I can allow zooming, the zooming works but it doesn't keep the UIImageView centered and ends up cutting off the bottom of 开发者_开发问答the image and leaves black space on top.

This is what I have:

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.

    scroller.bouncesZoom   = YES;
    scroller.clipsToBounds = YES;

    float scale = image.size.width/320;
    UIImage *scaled = [UIImage imageWithCGImage:[image CGImage] scale:scale orientation:UIImageOrientationUp];

    imageView = [[UIImageView alloc] initWithImage:scaled];
    imageView.userInteractionEnabled = YES;
    [imageView setCenter:CGPointMake(160,240)];

    [scroller addSubview:imageView];
    scroller.contentSize = [imageView frame].size;

    scroller.maximumZoomScale = 4.0;
    scroller.minimumZoomScale = 1.0;
    scroller.zoomScale        = 1.0;
}

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
    return imageView;
} 

Any suggestions?

I think this is what you want.

If pagination is not needed then disable pagination it works fine

scrollview.pagingEnabled = NO;

Below is the code I've used in my app (adapted from the WWDC sample) Maybe you can take something out of it :)

    CGSize imageSize =[image size];
    CGSize boundsSize = scrollview.bounds.size;
    CGRect frameToCenter = imageview.frame;

    // center horizontally
    if (frameToCenter.size.width < boundsSize.width)
        frameToCenter.origin.x = (boundsSize.width - frameToCenter.size.width) / 2;
    else
        frameToCenter.origin.x = 0;

    // center vertically
    if (frameToCenter.size.height < boundsSize.height)
        frameToCenter.origin.y = (boundsSize.height - frameToCenter.size.height) / 2;
    else
        frameToCenter.origin.y = 0;

    imageview.frame = frameToCenter;

    CGFloat xScale = boundsSize.width / imageSize.width;    // the scale needed to perfectly fit the image width-wise
    CGFloat yScale = boundsSize.height / imageSize.height;  // the scale needed to perfectly fit the image height-wise
    CGFloat minScale = MIN(xScale, yScale);                 // use minimum of these to allow the image to become fully visible

    // on high resolution screens we have double the pixel density, so we will be seeing every pixel if we limit the
    // maximum zoom scale to 0.5.
    CGFloat maxScale = 1.0 / [[UIScreen mainScreen] scale];

    // don't let minScale exceed maxScale. (If the image is smaller than the screen, we don't want to force it to be zoomed.) 
    if (minScale > maxScale) {
        minScale = maxScale;
    }

    scrollview.contentSize=imageSize;
    scrollview.maximumZoomScale=maxScale;
    scrollview.minimumZoomScale=minScale;
    scrollview.zoomScale=1;