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POSlight pause in scrolling animation (iPad)
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copied!<p>I am relatively new to programming on the iPad and I was trying to put together a simple program. Basically, it's a children's book and I need the functionality of a comic book style (or photo) viewer, where people swipe to change "pages" (or images).</p> <p>Each image is 1024x768. Currently, they are stored as JPGs because of the very large file sizes PNGs seem to produce. For this story, there are 28 pages.</p> <p>I took a look at the PageControl example, implementing a UIScrollView. On initialization, I create a big enough scrollview area. Then as the user scrolls, I load in the previous and next images. Again, just like the example only without implementing the page control at the bottom.</p> <p>The problem I am running into is a very slight pause in the animation when I am flipping. Once the images are loaded or cached, this doesn't happen. Now, I know the photo application doesn't do this and I'm not sure what is causing it.</p> <p>Here is my code for the scrollViewDidScroll method. I keep up with the page number and it will only call the loadPageIntoScrollView when a page has changed - I was thinking that the insane number of calls it was making was causing the slight pause in animation, but it turned out not to be the case. </p> <pre><code>- (void) scrollViewDidScroll: (UIScrollView *) sender { CGFloat pageWidth = scrollView.frame.size.width; int localPage = floor( (scrollView.contentOffset.x - pageWidth / 2 ) / pageWidth ) + 1; if( localPage != currentPage ) { currentPage = localPage; [self loadPageIntoScrollView:localPage - 1]; [self loadPageIntoScrollView:localPage]; [self loadPageIntoScrollView:localPage + 1]; } } // scrollViewDidScroll </code></pre> <p>And here is my <code>loadPageIntoScrollView</code> method. I'm only creating a UIImageView and loading an image into that - I don't see how that could be much "leaner". But somehow it's causing the pause. Again, it's not a HUGE pause, just one of those things you notice and is enough to make the scrolling look like it has a very. very slight hiccup.</p> <p>Thank you in advance for any help you could provide.</p> <pre><code> - (void) loadPageIntoScrollView: (int)page { if( page < 0 || page >= kNumberOfPages ) return; UIImageView *controller = [pages objectAtIndex:page]; NSLog( @"checking pages" ); if( (NSNull *)controller == [NSNull null] ) { UITapGestureRecognizer *singleTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleSingleTap:)]; NSString *pageName = [[NSString alloc] initWithFormat:@"%d.jpg", page]; controller = [[UIImageView alloc]initWithImage:[UIImage imageNamed:pageName]]; [controller setUserInteractionEnabled:YES]; [controller addGestureRecognizer:singleTap]; [pages replaceObjectAtIndex:page withObject:controller]; [controller release]; } // if controller == null // add the page to the scrollview if( controller.superview == nil ) { NSLog(@"superview was nil, adding page %d", page ); CGRect frame = scrollView.frame; frame.origin.x = frame.size.width * page; frame.origin.y = 0; controller.frame = frame; [scrollView addSubview:controller]; } // if } // loadPageIntoScrollView </code></pre>

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