Delegates and Notifications

Delegates and Notifications

An object that has made itself the delegate of a standard Cocoa object is probably interested in receiving notifications from that object as well. For example, if you have implemented a delegate to handle the windowShouldClose: delegate method for a window, that same object is likely to be interested in the NSWindowDidResizeNotification from that same window.

If a standard Cocoa object has a delegate and posts notifications, it is automatically registered as an observer for the methods the object implements. If you are implementing such a delegate, how would you know what to call the method?

The naming convention is simple: Start with the name of the notification. Remove NS from the beginning, and make the first letter lowercase. Remove Notification from the end. Add a colon. For example, to be notified that the window has posted anNSWindowDidResizeNotification, the delegate would implement the following method:

- (void)windowDidResize:(NSNotification *)aNotification

This method will be called automatically after the window resizes. You can also find this method listed in the documentation and header files for the class NSWindow.