
440 9 Chapter 20: Visualization: Views and Windows
overhead and you don't have to worry about the representa-
tion.
NSImage
NSImage is responsible for managing all of its representations
and for selecting (and drawing) the appropriate one for a giv-
en device. For convenience, images may be named.
Each NSImage may have a delegate that implements image-
DidNotDraw (aRect--NSRect). This method is called only if
NSImage was unable to draw the image. It returns an NSIm-
age*--which could be an alternative image to draw. If it re-
turns nil, NSImage no longer tries to draw the image,
assuming either that the delegate has done so or