Observer Design Pattern

Observer pattern deals in communication between objects. It defines a one-to-many relationship, when an object changes state it notifies a list of objects. Observer pattern is classified as the behavioral design pattern. It ultimately helps decouple senders and receivers.

Radio station can be an example for this pattern, as we all know it broadcasts music to all it’s listeners. As long as listeners are interested (or rather driving car) they listen to radio and before they are off to work, they turn it off and no longer receives the broadcast but radio station doesn’t stop broadcasting so, whenever listeners are interested they can join in.

Let’s see an Example:

Apple platform have a similar component called NSNotificationCenter in Swift it is NotificationCenter. We can use NotificationCenter to send and receive notifications.

Pros:

— Makes Sender and Listeners loosely coupled

— Sender and Listeners are independent of each other, therefore, changes will not affect each other.

Cons:

— If misused, it can add complexity and lead to performance issues, like not unsubscribing even when listener is not listening.

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