content jumps on zooming out with UIScrollView
I created a quick sample project and had the same issue you described using the code you pasted. I don't exactly know what the "proper" way to zoom is in iOS but I found this tutorial which says that you need to recenter your contentView after the scrollView has been zoomed. I would personally expect it to be automatically re-centered given that it is the view you're returning in the viewForZoomingInScrollView delegate method but apparently not.
- (void)centerScrollViewContents {
CGSize boundsSize = _scrollView.bounds.size;
CGRect contentsFrame = _contentView.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;
}
_contentView.frame = contentsFrame;
}
- (void)scrollViewDidZoom:(UIScrollView *)scrollView {
// The scroll view has zoomed, so we need to re-center the contents
[self centerScrollViewContents];
}
The code above is not written by me but is simply copied from the tutorial. I think its pretty straightforward. Also, centring the contentView seems to be a lot more elegant then constantly changing the bounds and content size of the scrollview so give it a try.