How do I dynamically add images to a UIScrollView?

I'm working on an an app that updates both a UITableView and a UIScrollView. I like how UITableView updating works. As I add, remove, or update items, I call insertRowsAtIndexPaths:withRowAnimation:, reloadRowsAtIndexPaths:withRowAnimation:, and deleteRowsAtIndexPaths:withRowAnimation: as appropriate. However, updating the UIScrollView has turned out to be more of a challenge.

So how can I do it? My UIScrolLView contains images, and I want to be able to insert, update, and remove individual images -- with animation -- efficiently and smoothly, and perhaps in random order. How does one do this sort of thing?

As an example, I have code like this in my UIScrollViewDelegate implementation for adding a new image:

if (newImageindex == currentImageIndex) {
    [scrollView setNeedsDisplay];
    [scrollView setContentOffset:portalView.contentOffset animated:YES];
} else if (newImageIndex < currentImageIndex) {
    currentImageIndex++;
    CGPoint offset = portalView.contentOffset;
    offset.x += portalView.frame.size.width;
    portalView.contentOffset = offset;
}

This is close, I think, but not quite right. I end up with the images added, but the UIScrollView seems to scroll to a position before the first image in the view. If I start scrolling it by hand, the first image appears. It's like it's scrolled to position -1 in my images.

The example may not help to highlight my problem much, but surely it's a common need to dynamically rejigger the images appearing in a UIScrollView. What's the state of the art on this?

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How do I dynamically add images to a UIScrollView?

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