Learning Objective-C — Informal Protocol

Use formal protocol with @optional instead of informal protocol

One of the nice thing about new Objective-C 2.0 is the introduction of @optional and @required keyword of protocol declaration. Prior to Objective-C 2.0 (released in Mac OS X Leopard and after), you can only declared informal protocol using category to NSObject.
Now all you need to do is to declare the optional methods with @optional keyword. This is a much welcomed feature because this allows better compile-time type checking, as well as better readability.

The delegate pattern makes use of this Objective-C feature, for example, NSApplicationDelegate.

@protocol NSApplicationDelegate
@optional
- (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication *)sender;
:

Most (if not all) of the Cocoa API from Apple have been rewritten in this fashion.

http://developer.apple.com/mac/library/releasenotes/Cocoa/Foundation.html

So make good use of it.

About these ads

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s