Subclassing an UIView efficiently

Question

Guys I'm having some troubles subclassing an UIView. I'm creating an IconView. Simply it's a container for some other subviews. In my IconView i have this iVar: UIImageView _background UIImageView _icon UILabel _iconLabel.

When I initialize the IconView I setup this 3 iVar with images, text and some quartz effect like roundCorner and Shadow and then I add them to the self view. Everything is Ok but if I insert some of this IconView (i.e. 10) inside an empty scrollview the scroll effect is not smooth. I tried before inserting thousand of simple UIViews in a scrollview and the scroll animation works perfectly. With just 10 of my IconView the scroll animation works really bad.

I could approach differently retaining UIImages instead of UIImageViews and draw it inside drawRect: method but in this case I'm gonna loose Autoresizing property and Quartz effect.

Any suggests? Thank, Gabriele.

Answer 1

Unfortunately, a UIScrollView gets slow pretty fast. There are a lots of posts and articles on this topic out there, like this Question and this (defect) blogpost along with it's sample code. There are also three sessions about 'Performance optimization in iOS' in the 2010's WWDC videos which I highly recommend to watch. To summarize the conclusions: Use as few subviews as you can and take special care of avoiding transparencies.

Ok, so much for the general 'Performance in ScrollViews' talk, now to your case: Having the same problem, I used all the tips from the articles and videos above and while they improved the performance, it just wasn't enough. I had, like you, used rounded corners one some images and I found out that this absolutely kills performance. Just deactivating them helped more than everything else. It's probably the same with the shadow effects.

Now, most likely, you want to keep those rounded corners. I would suggest that you create a copy of your images (or take the original, if possible) and than manipulate them directly, using those awesome classes. This way, the effects will only be applied once. It works perfectly for me. For you shadows, you can probably just create some in Photoshop and use them in a new ImageView.

If that isn't enough, you should try to cache your IconViews, like TableViewCells are cached, if you don't already do this.

Answer 2

The problem will probably be the Quartz shadows. They can really slow the rendering down if used a lot.

Before you write them off, you might try setting your CALayer's shouldRasterize property to YES. This makes quartz render the shadow only once and store it in a buffer. See how it goes.