Center an UIImageView on the screen when zoom out

I have an UIImageView inside an UIScrollView. I want that the user can zoom and navigate the image.

This is my work code:

//img is the UIImageView //scroller is the UIScrollView - (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView { return img; } - (void)viewDidLoad { [super viewDidLoad]; UIImage *image = [UIImage imageNamed:@"map_screen.png"]; img = [[UIImageView alloc] initWithImage:image]; scroller.delegate = self; scroller.autoresizesSubviews = YES; scroller.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth; scroller.contentSize = img.frame.size; scroller.scrollEnabled = YES; scroller.directionalLockEnabled = NO; scroller.userInteractionEnabled = YES; CGSize ivsize = img.frame.size; CGSize ssize = scroller.frame.size; float scalex = ssize.width / ivsize.width; float scaley = ssize.height / ivsize.height; scroller.minimumZoomScale = fmin(1.0, fmax(scaley, scalex)); scroller.zoomScale = fmin(1.0, fmax(scalex, scaley)); [scroller addSubview:img]; img.userInteractionEnabled = YES; }

all works, but this happened: the minimum zoom is the height of the screen. My image has the width bigger than the height, so i want that the minumum zoom is the width.

If i write

scroller.minimumZoomScale = fmin(1.0, scalex);

works, but when the user zooms out, the image is not at the center of the screen, but at the top.

i've tried something like this

CGPoint scrollCenter = [scroller center]; [img setCenter:CGPointMake(scrollCenter.x, scrollCenter.y)];

or =;

but with this solution, the image is not completly scrollable, and if i zoom out, it stay again at the top of the screen, but is not completly visible!

What can i do for fix it?

-------------Problems Reply------------

You have to do it manually while the zooming is in progress using the scrollViewDidZoom delegate function... something like

- (void)scrollViewDidZoom:(UIScrollView *)scrollView

// center the image as it becomes smaller than the size of the screen
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;


Category:iphone Views:1 Time:2011-04-29

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