Overriding drawRect & memory

[twitter-archive]

Overriding drawRect & memory

[joshaber]

Take a look in -[TUIView displayLayer:]. If you don't implement -drawRect: then the view doesn't have to create a backing store. That saves time and memory.

Also note that if your view just needs a background color and nothing else, it's much more efficient to implement that by setting the backgroundColor property instead of implementing -drawRect: and filling manually. That's because CALayer has a built-in fast path for drawing a filled view that also avoids the need to create a backing store.

[joshaber]

(And if you come from UIKit land, the same is true there. UIView only creates a backing store if your subclass implements -drawRect:.)

[mrjjwright]

Oh yes, I read about this in the comments of the Chameleon UIView implementation and how it handles displayLayer and displayLayer:inContect. BigZaphod notes that the basic machinery is as follows:

// Here's how CALayer appears to work:
// 1- something call's the layer's -display method.
// 2- arrive in CALayer's display: method.
// 2a-  if delegate implements displayLayer:, call that.
// 2b-  if delegate doesn't implement displayLayer:, CALayer creates a buffer and a context and passes that to drawInContext:
// 3- arrive in CALayer's drawInContext: method.
// 3a-  if delegate implements drawLayer:inContext:, call that and pass it the context.
// 3b-  otherwise, does nothing

Thanks Josh, this is very helpful to understand when creating simple container views!