Implement NSNotificationCenter using Swift!

If NSNotificationCenter didn’t exist, how might you implement it?

You have to think quite deeply about NSNotificationCenter, what it does and how it might work.

Terminology

NSNotificationCenter: A notification dispatch mechanism that enables the broadcast of information to registered observers.

Observers: An object that subscribes to an observable and responds the the message(s) that are send.

Observable: In this case NSNotification, and object than can be subscribed to.

Subscribe: An observer subscribes to an observable in order to register to be sent messages.

The problem

NSNotification broadcasts information to the observers when they are subscribed to it. In all probability, NSNotification is probably a Singleton. When you add an observer, it gets moved into what is probably an array of observers (delegate).

When you remove an observer, it is removed from the array of observers.

When you post a notification, NSNotification loops through the array of observers and initiates the callback method assigned with each delegate in the array.

The Approach

Since we are using Swift, a protocol-based approach will be helpful to us.

The subscriber class will use a simple callback mechanism for receiving the messages from NSNotificationCenter where we declare an Observer:

which is then involved in the following subscriber class:

Related posts:

Smartphone Paper Prototyping Frame

We UX Designers conduct a usability testing after creating a lo-fi interface design to test if a user can understand and navigate the screens. Then, we iterate the design over and over again until it… Read more

Statement from Chairman John Stanton on Seattle Mariners workplace culture

Today the Seattle Times published a story about the Seattle Mariners workplace environment. We do not believe it accurately reflects the values and culture of our organization. I want to be very… Read more

What Is the Difference Between Cryptocurrency Trading and Stocks Trading?

Many investors who want to enter the cryptocurrency market have never before encountered such financial instruments. However, most of them have at least some understanding of the stock market. But… Read more