Why do I get a “Can’t cache image” error when I try alloc’ing an NSImage?
It’s a bit difficult to answer this question because NSImage is a complex class and you haven’t provided any code, so it is not known exactly what you’re doing wrong. It sounds like you’re only alloc’ing and initing an NSImage without adding any imagerep to it (e.g. an NSBitmapImageRep). If so, the page on this site describing NSBitmapImageRep has some example code showing how to create an imagerep suitable for drawing. You might find it useful.
I get a “Can’t cache image” error when the size of my image is 0.0 or negative in either dimension.
The reason for this exception is given in the documentation of NSImage:
This method does not add any image representations to the image object.. It is permissible to initialize the receiver by passing a size of (0.0, 0.0); however, the receiver�s size must be set to a non-zero value before the NSImage object is used or an exception will be raised.
Removed non-essential parts in this discussion.