Masking a UIView

I use the following code all the time in my view controller:

UIView *view = [[CustomView alloc] init]; UIView *mask = [[CustomMask alloc] init]; [view layer].mask =[mask layer]; 

and it masks the view as I want.

However, when it is not in a view controller I get the error:

'Request for member 'mask' in something not a structure or a union'

E.g. I want to apply the mask in the CustomView class itself. So I would have:

UIView *mask = [[CustomMask alloc] init]; [self layer].mask =[mask layer]; 

This produces the error. If I do it in my AppDelegate class with two images I get the same error again.

Can anyone explain how I can get the result I want.

Many thanks