I'm trying to learn how to use and implement CALayer
in a Mac Objective-C application, but I can't seem to probably do the most basic thing - add a new layer and set its background colour/frame size. Can anyone see what is wrong with my code?
CALayer *layer = [CALayer layer];
[layer setFrame:CGRectMake(0, 0, 100, 100)];
[layer setBackgroundColor:CGColorCreateGenericRGB(1.0, 0.0, 0.0, 1.0)];
[self.layer addSublayer:layer];
[layer display];
I put this in the - (void)drawRect:(NSRect)rect
method of my custom NSView
subclass, but when I run the application, it just shows a blank view, with no background colour or evidence of the layer I created.
First of all, you don't want to add a layer in the drawRect:
method of a view, this gets called automatically by the system and you'd probably end up with a lot more layers than you actually want. initWithFrame:
or initWithCoder:
(for views that are in a nib file) are better places to initialize your layer hierarchy.
Furthermore, NSView
s don't have a root layer by default (this is quite different from UIView
on iOS). There are basically two kinds of NSView
s that use a layer: layer-backed views and layer-hosting views. If you want to interact with the layer directly (add sublayers etc.), you need to create a layer-hosting view.
To do that, create a CALayer
and call the view's setLayer:
method. Afterwards, call setWantsLayer:
. The order is important, if you'd call setWantsLayer:
first, you'd actually create a layer-backed view.