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    <p>Yay! I tried to approach the problem with just one UIScrollView, and I think I found a solution.</p> <p>Before the user starts zooming (in <code>viewForZoomingInScrollView:</code>), I switch the scroll view into zooming mode (remove all additional pages, reset content size and offset). When the user zooms out to scale 1.00 (in <code>scrollViewDidEndZooming:withView:atScale:</code>), I switch back to paging view (add all pages back, adjust content size and offset).</p> <p>Here's the code of a simple view controller that does just that. This sample switches between, zooms and pans three large UIImageViews.</p> <p>Note that a single view controller with a handful of functions is all it takes, no need to subclass UIScrollView or something.</p> <pre><code>typedef enum { ScrollViewModeNotInitialized, // view has just been loaded ScrollViewModePaging, // fully zoomed out, swiping enabled ScrollViewModeZooming, // zoomed in, panning enabled ScrollViewModeAnimatingFullZoomOut, // fully zoomed out, animations not yet finished ScrollViewModeInTransition, // during the call to setPagingMode to ignore scrollViewDidScroll events } ScrollViewMode; @interface ScrollingMadnessViewController : UIViewController &lt;UIScrollViewDelegate&gt; { UIScrollView *scrollView; NSArray *pageViews; NSUInteger currentPage; ScrollViewMode scrollViewMode; } @end @implementation ScrollingMadnessViewController - (void)setPagingMode { NSLog(@"setPagingMode"); if (scrollViewMode != ScrollViewModeAnimatingFullZoomOut &amp;&amp; scrollViewMode != ScrollViewModeNotInitialized) return; // setPagingMode is called after a delay, so something might have changed since it was scheduled scrollViewMode = ScrollViewModeInTransition; // to ignore scrollViewDidScroll when setting contentOffset // reposition pages side by side, add them back to the view CGSize pageSize = scrollView.frame.size; NSUInteger page = 0; for (UIView *view in pageViews) { if (!view.superview) [scrollView addSubview:view]; view.frame = CGRectMake(pageSize.width * page++, 0, pageSize.width, pageSize.height); } scrollView.pagingEnabled = YES; scrollView.showsVerticalScrollIndicator = scrollView.showsHorizontalScrollIndicator = NO; scrollView.contentSize = CGSizeMake(pageSize.width * [pageViews count], pageSize.height); scrollView.contentOffset = CGPointMake(pageSize.width * currentPage, 0); scrollViewMode = ScrollViewModePaging; } - (void)setZoomingMode { NSLog(@"setZoomingMode"); scrollViewMode = ScrollViewModeInTransition; // to ignore scrollViewDidScroll when setting contentOffset CGSize pageSize = scrollView.frame.size; // hide all pages besides the current one NSUInteger page = 0; for (UIView *view in pageViews) if (currentPage != page++) [view removeFromSuperview]; // move the current page to (0, 0), as if no other pages ever existed [[pageViews objectAtIndex:currentPage] setFrame:CGRectMake(0, 0, pageSize.width, pageSize.height)]; scrollView.pagingEnabled = NO; scrollView.showsVerticalScrollIndicator = scrollView.showsHorizontalScrollIndicator = YES; scrollView.contentSize = pageSize; scrollView.contentOffset = CGPointZero; scrollViewMode = ScrollViewModeZooming; } - (void)loadView { CGRect frame = [UIScreen mainScreen].applicationFrame; scrollView = [[UIScrollView alloc] initWithFrame:frame]; scrollView.delegate = self; scrollView.maximumZoomScale = 2.0f; scrollView.minimumZoomScale = 1.0f; UIImageView *imageView1 = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"red.png"]]; UIImageView *imageView2 = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"green.png"]]; UIImageView *imageView3 = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"yellow-blue.png"]]; // in a real app, you most likely want to have an array of view controllers, not views; // also should be instantiating those views and view controllers lazily pageViews = [[NSArray alloc] initWithObjects:imageView1, imageView2, imageView3, nil]; self.view = scrollView; } - (void)setCurrentPage:(NSUInteger)page { if (page == currentPage) return; currentPage = page; // in a real app, this would be a good place to instantiate more view controllers -- see SDK examples } - (void)viewDidLoad { scrollViewMode = ScrollViewModeNotInitialized; [self setPagingMode]; } - (void)viewDidUnload { [pageViews release]; // need to release all page views here; our array is created in loadView, so just releasing it pageViews = nil; } - (void)scrollViewDidScroll:(UIScrollView *)aScrollView { [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(setPagingMode) object:nil]; CGPoint offset = scrollView.contentOffset; NSLog(@"scrollViewDidScroll: (%f, %f)", offset.x, offset.y); if (scrollViewMode == ScrollViewModeAnimatingFullZoomOut &amp;&amp; ABS(offset.x) &lt; 1e-5 &amp;&amp; ABS(offset.y) &lt; 1e-5) // bouncing is still possible (and actually happened for me), so wait a bit more to be sure [self performSelector:@selector(setPagingMode) withObject:nil afterDelay:0.1]; else if (scrollViewMode == ScrollViewModePaging) [self setCurrentPage:roundf(scrollView.contentOffset.x / scrollView.frame.size.width)]; } - (UIView *)viewForZoomingInScrollView:(UIScrollView *)aScrollView { if (scrollViewMode != ScrollViewModeZooming) [self setZoomingMode]; return [pageViews objectAtIndex:currentPage]; } - (void)scrollViewDidEndZooming:(UIScrollView *)aScrollView withView:(UIView *)view atScale:(float)scale { NSLog(@"scrollViewDidEndZooming: scale = %f", scale); if (fabsf(scale - 1.0) &lt; 1e-5) { if (scrollView.zoomBouncing) NSLog(@"scrollViewDidEndZooming, but zoomBouncing is still true!"); // cannot call setPagingMode now because scrollView will bounce after a call to this method, resetting contentOffset to (0, 0) scrollViewMode = ScrollViewModeAnimatingFullZoomOut; // however sometimes bouncing will not take place [self performSelector:@selector(setPagingMode) withObject:nil afterDelay:0.2]; } } @end </code></pre> <p>Runnable sample project is available at <a href="http://github.com/andreyvit/ScrollingMadness/" rel="nofollow noreferrer">http://github.com/andreyvit/ScrollingMadness/</a> (if you don't use Git, just click Download button there). A README is available there, explaining why the code was written the way it is.</p> <p>(The sample project also illustrates how to zoom a scroll view programmatically, and has ZoomScrollView class that encapsulates a solution to that. It is a neat class, but is not required for this trick. If you want an example that does not use ZoomScrollView, go back a few commits in commit history.)</p> <p>P.S. For the sake of completeness, there's TTScrollView — UIScrollView reimplemented from scratch. It's part of the great and famous <a href="http://github.com/joehewitt/three20/" rel="nofollow noreferrer">Three20 library</a>. I don't like how it feels to the user, but it does make implementing paging/scrolling/zooming dead simple.</p> <p>P.P.S. The real Photo app by Apple has pre-SDK code and uses pre-SDK classes. One can spot two classes derived from pre-SDK variant of UIScrollView inside PhotoLibrary framework, however it is not immediately clear what they do (and they do quite a lot). I can easily believe this effect used to be harder to achieve in pre-SDK times.</p>
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