UIScrollView zoom is not working properly - ios

Question

Whenever I click on an image, I want the image to display as a larger image with the ability to zoom. So far when I click on the image, it displays as I want it to inside a scrollview. However, I have to get lucky to be able to zoom in properly. Most of the time when I attempt to zoom, the image just moves down and to the right and does not zoom at all. Here is my code:
-(void) pictureButtonAction
{
self.scrollImageView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height)];
self.scrollImageView.contentSize = self.fullImageView.image.size;
self.scrollImageView.delegate = self;
self.scrollImageView.clipsToBounds = YES;
self.scrollImageView.scrollEnabled = YES;
[self.scrollImageView setMaximumZoomScale:4.0f];
[self.scrollImageView setMinimumZoomScale:1.0f];
[self.view addSubview:self.scrollImageView];
[self.scrollImageView addSubview:fullImageView];
}
-(UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView
{
return self.fullImageView;
}

Answer 1

ImageViews frame got changed while zooming , so that it moves down. So, You have to centralize the image view each time you zoom .
your scrollviews contentsize should be greater than or equal to your image size , if your fullImageView.image.size is less than your scrollviews bounds ,then set your scrollviews contentSize atleast double the scrollviews bounds .
call the below function in scrollViewDidZoom delegate method
-(void) centerScrollViewContents
{
CGSize boundsSize = self.scrollView.bounds.size;
CGRect contentsFrame = self.imageView.frame;
if (contentsFrame.size.width < boundsSize.width) {
contentsFrame.origin.x = (boundsSize.width - contentsFrame.size.width) / 2.0f;
} else {
contentsFrame.origin.x = 0.0f;
}
if (contentsFrame.size.height < boundsSize.height) {
contentsFrame.origin.y = (boundsSize.height - contentsFrame.size.height) / 2.0f;
} else {
contentsFrame.origin.y = 0.0f;
}
self.imageView.frame = contentsFrame;
}
Try this , hope it will help you ; happy coding ! :)

Answer 2

#Maria's answer works but when zooming you'll experience unwanted bounces, instead of using it under scrollViewDidZoom, use scrollViewDidEndZooming: delegate to prevent that..
- (void)scrollViewDidEndZooming:(UIScrollView *)scrollView withView:(UIView *)view atScale:(CGFloat)scale
{
[self centerScrollViewContents];
}
and with a little enhancement from her code:
[UIView animateWithDuration:0 animations:^{
self.previewImageView.frame = contentsFrame;
}];
a bit late for an answer but i hope this will be useful to some..