UIView's contentScaleFactor depends on implementing drawRect:?

Question

I have stumbled on a weird thing. It looks like UIView\'s contentScaleFactor is always 1, even on Retina devices, unless you implement drawRect:<

Answer 1

Presumably, if you don't override drawRect: then UIKit knows that a UIView doesn't draw anything so it takes the (presumably) fast case of having a layer that has a content scale of 1. As soon as you override drawRect: though, it knows it needs to set up a layer that is of the correct content scale that you can draw into if you want to. It doesn't know that you do nothing in drawRect: though so it can't make the same assumption as before.

In fact all that is alluded to in the docs:

For views that implement a custom drawRect: method and are associated with a window, the default value for this property is the scale factor associated with the screen currently displaying the view.

Why don't you just override drawRect: and in that, draw your image? Or you could probably get away with what you're currently doing and have a stub drawRect:. Given what the docs say, I'd say that's perfectly reasonable to assume it's going to continue to work and is correct behaviour.