namespace ObserverDesignPatternĬreate a class file with the name Observer.cs and then copy and paste the following code in it. The Observer defines an updating interface for objects that should be notified of changes in a Subject. So notifying all Registered users ") įoreach (IObserver observer in observers)Ĭreate a class file with the name IObserver.cs and then copy and paste the following code in it. Public void RemoveObserver(IObserver observer)
Public void AddObservers(IObserver observer) Public void RegisterObserver(IObserver observer)Ĭonsole.WriteLine("Observer Added : " + ((Observer)observer).UserName ) Public void setAvailability(string availability)Ĭonsole.WriteLine("Availability changed from Out of Stock to Available.") Public Subject(string productName, int productPrice, string availability) The ConcreteSubject objects store the states of interest to the Observers and also responsible for sending the notification to its observers when its state changes. Void RegisterObserver(IObserver observer) Ĭreate a class file with the name Subject.cs and then copy and paste the following code in it. The Subject knows its Observers and provides an interface for adding or removing any number of Observer objects. Step1: Creating the Subject interfaceĬreate a class file with the name ISubject.cs and then copy and paste the following code in it. Let us see the step by step implementation of the Observer Design Pattern in C#. Out of Stock to Available the Subject will send a notification to all the subscribers.
In our case, the three users are registered to the notification option of the Subject. For better understanding please have a look at the following image.Īs per the Observer Design Pattern, the Observers need to be registered to the Subject. User1, User2, and User3) are the Observers. In our examples, the Mobile is the Subject and three users (i.e. As we already discussed the Observer Design Pattern has two main components i.e. So, what Amazon will do is send notifications to all the users who are registered. What the above three users do is, they registered with the above option, so that when the product is available, the Amazon site will send a notification to them.Īfter a few days, the Product is available, and so the status is changed from Out Of Stock to available. On the Amazon site, there is an option called to notify me when the product is available. But the above three users want to buy that particular mobile. Unfortunately, at that time the Mobile phone is out of stock i.e. Here, we are taking the example of Amazon.Īs you can see in the above image, three users come to the Amazon site for buying a Mobile Phone. Please have a look at the following diagram. Let us understand the Observer Design Pattern with an example. A real-time example of the Observer Design Pattern: Once the observer gets the notification from the subject, it will call one of the methods of the subject to get the change state data. Whenever there are some changes that occurred in the state, then the subject will notify all the observers which are registered in the subject by calling one of the observer methods. Again if any observer wants to unregister then he/she simply needs to call the unregister method of the subject. If any new observer wants to register then he/she needs to call the Register method of the Subject. As you can there are three observers are registered within the subject. The Subject having methods to Register and unregister the observers. Please have a look at the following diagram.Īs shown in the above image, we can define the Subject as an object which maintains a list of observers. They simply listen to the changes in the subjects.Īnother name of the Observer is the Listener. When a change occurs to a subject it should notify all of its subscribers. The observer design pattern is having two main components. How does the Observer Design Pattern work? The Other names of this pattern are Producer/Consumer, Publish/Subscribe. The Observer Design Pattern defines a one-to-many dependency between objects so that when one object’s state changes, all its dependents are notified and updated automatically.
#Observer pattern software#
The Observer Design Pattern is a Software Design Pattern in which an object (called as Subject) maintains a list of its dependents (called as Observers) and notifies them automatically whenever any state changes by calling one of their methods. When to use the Observer Design Pattern in C#?Īccording to GoF, the Observer design Pattern should “Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically”.Example to understand the Observer Design Pattern in C#.
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