iPhone - UIView adding a subView vs drawRect?

Question

What are the differences between adding a view as a subView VS drawing the view in that view's drawRect method?.

I use both approaches, but I was wondering apart from the obvious such as, if you do in drawRect it will be a single View, as opposed as two views, or adding as a subview is just easier. Are there any specific situations where you should definitely use one over the other?

score 4 · Accepted Answer · answered Jan 12 '12 at 21:36

4

Overriding -drawRect: can be a good way to draw complex UITableViewCells. Having all of the subviews composited and drawn as one view helps table view scrolling performance immeasurably.

Having said that, I typically stick with the highest level API available and drop down to a lower level only if performance suffers.

answered Jan 12 '12 at 21:36

Mark Adams

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Thanks for this. In my app, cells can have lots of subviews (no limit, but usually between 5 and 20), and I've been reported that with the 3GS it's not really smooth. Now I have an idea why! – ksol Jan 12 '12 at 21:41
It's a huge problem if those subviews have any alpha at all. The GPU is definitely working hard trying to do all that compositing for every frame in 1/60th of a second. If the drawing doesn't finish in time, that frame is dropped resulting in a choppy performance. – Mark Adams Jan 12 '12 at 21:42
the subviews are custom labels with a gradient background, I don't tweak with opacity. But still, might come from that – ksol Jan 12 '12 at 21:45

score 4 · Answer 2 · answered Jan 12 '12 at 21:40

Adding a subview is easier as you point out, and I really see this as no contest in 90% of cases. You should generally add a subview and let the libraries handle drawing of subviews in their correct position.

I only use -drawRect: to accomplish custom drawing within my view, but not to draw subviews, it creates unnecessary complexity. If you need a lot of performance, -drawRect: can help you there. Also, in the case of simple drawing, -drawRect: is very nice as opposed to making several subviews. But in general, it pays to just add a subview.

If in the future you decide you want these subviews to receive touch events or handle things interactively, it is more difficult to refactor your -drawRect: code.

iPhone - UIView adding a subView vs drawRect?

2 Answers2