What follows is a quick introduction to working with protocols. This is good background information to understand as protocols are common in various Cocoa frameworks. A protocol is means to define a list of required and/or optional methods that a class implements. If a class adopts a protocol, it must implement all required methods in the protocols it adopts.

Cocoa uses protocols to support interprocess communication through Objective-C messages. In addition, since Objective-C does not support multiple inheritance, you can achieve similar functionality with protocols, as a class can adopt more than one protocol.
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What follows is a brief guide to working with Notifications in Cocoa. I’ll cover the basics, including registering an observer and posting notifications, just enough to start using notifications in your apps.

There is an instance of NSNotificationCenter available to every running application. This class acts as an intermediary to facilitate communication between objects that are interested in being notified at some point in the future (these objects are known as the observers) and a poster that posts to the notification center, resulting in all observers (registered for a specific notification) being called.
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Subtle typos and the problems they bring, it’s enough to drive one nuts. Let me share a recent experience that will shed some light on my most recent experience. Below is a short snippet of code that show something similar to what I was recently attempting to do. It’s nothing more than a variable definition, and in one place incrementing the variable, in another I decrementing.
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