Question

So, UITableView supports essentially “infinite” scrolling. There’ may be a limit but that sucker can scroll for a looonnnggg time. I would like to mimic this behavior with a UIScrollView but there are two fundamental impediments:

1) scrollView.contentSize is fixed at creation time.
2) zooming can blow any lazy-loading scheme all to hell since it can cause infinte data explosion.

Have others out there pondered this idea? Yah, I know, we are essentially talking about re-creating Google Maps here. Any insights would be much appreciated.

Cheers,
Doug

Answer 1

While it’s impossible to have a truly infinite UIScrollView, there are some simple tricks you can use to emulate that behavior.

1. Handling the fixed contentSize: have some fixed-size view handled by your scroll view, and at launch or instantiation, set the content offset so that you’re seeing the middle of the handled view. Then just watch the content offset (using KVO or some other method), and if you near any edge, update the content of the view with a new set of content (offset appropriately) and reset the scroll view’s contentOffset property to be back in the middle.
2. Handling zooming: do something similar, only this time watch the zoom factor on the scroll view. Whenever it gets to a certain point, do some manipulation to whatever data you’re presenting so that it appears zoomed, then reset the zoom factor to 1.0. For example, if you’re scrolling an image and it gets zoomed to appear twice as large, programmatically apply some kind of transform to make the image twice as large, then reset the scroll view’s zoom factor to 1.0. The image will still appear zoomed in, but the scroll view will be able to continue zooming in further as necessary. (Google Maps takes this one step further where it lazy-loads more detailed views as the user zooms – you may or may not choose to implement this.)