Enpatika

In general, the most relevant SOLID principle related to Observer is the Open/Close Principle : Once you have written the code of the observed object, you need not change the code when you want additional observers to know it, yet it is easy to add such observers – this is exactly what “closed for modifications, open …

The Observer Pattern is the foundation of the Model View Controller (MVC) pattern, in which a view is updated automatically whenever the model’s state changes . … The subject interface defines a contract for attaching and detaching an observer to the subject, as well as notification of changes to any attached observers.

Observer is a behavioral pattern. Decorator is a structural pattern . Using observer implements event handling (it binds some method calls of different classes with each other).

Observer is a behavioral design pattern that lets you define a subscription mechanism to notify multiple objects about any events that happen to the object they’re observing.

The observer pattern is a software design pattern in which an object, named the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.

The Observer Design Pattern is also known as the Event-Subscriber or the Listener pattern .