UIScrollView performance problem because of lots of labels

Question

I've got a pretty big UIScrollView (contentSize 8000 x 960) with a lot of small labels.

The labels are only added if you scroll to the area where the label belongs to. So, at first, the scrooling is smooth, but as more and more labels are loaded, the performance suffers more and more.

What's the best solution to keep the scrolling smooth? Is CATiledLayer the way to go? Or should the labels off the view should be hidden or something like that?

Thanks a lot for your help!

Stefan

EDIT: I got a huge performance boost when drawing some objects instead of using views; but now, I've got another problem; if I draw directly onto the UIScrollView, everything performs great. But if I lay a UIView on the UIScrollView and draw on that, performance goes down again (both times calling setNeedsDisplayInRect: in scrollViewDidScroll:).

So hierarchy:
UIWindow
UIView
UIScrollView <== drawing here

works fine.

But hierarchy:
UIWindow
UIView
UIScrollView (size 8000x960)
UIView (size 8000 x 960) <== drawing here

performs bad.

Any ideas why? I need the UIView above because the drawing should be ABOVE some UIViews; so I place the UIViews in the scrollView and draw in the view above...

Answer 1

The label reuse is one of possible solutions. Sometimes it doesn't help a lot. When a new UIView appears the drawRect method will be called and that may cause problems with animation.

Sometimes the best solution is to draw your labels (I mean text) directly using Core Graphics without creating UILabel object or something else. The CALayer will increase performance, but there is a possibility that it will not help you a lot.

But first of all you should remember that views with alpha = 0 or hidden = YES will not be drawn at all, so there is no penalty for using them. Maybe you should try to hide unused ones before using Core Graphics.