Cocoa in a Nutshell

Working with Images

NSImage and NSImageRep are Cocoa’s image-handling workhorses. NSImage provides a convenient and easy-to-use frontend to a powerful and flexible backend comprised of NSImageRep’s many subclasses. NSImage provides a high level interface for loading, saving, and drawing images onscreen. NSImageRep and its subclasses, on the other hand, provide interfaces for working with specific image formats.

NSImage

NSImage provides the high-level interface for working with images, which includes the ability to load and save images and draw them to screen. With NSImage, you don’t need to worry about image formats, which are handled internally by NSImage and the NSImageRep set of classes. To initialize instances of NSImage use these methods:

• initByReferencingFile:

• initByReferencingURL:

• initWithContentsOfFile:

• initWithContentsOfURL:

• initWithData:

• initWithPasteboard:

• initWithSize:

When you initialize anything by reference, as with the first two methods, the data is not loaded until the object actually needs it. This contrasts with initWithContents..., which loads the data and initializes the object immediately. The last method, initWithSize:, initializes an empty image.

imageNamed: is a useful method for creating image objects with images contained in the application bundle. With this method, you don’t have to provide a path to the file or include the file extension in the name—NSImage knows where to find it within the bundle.

NSImageView

NSImageView is a subclass of NSControl ...