Difference Between Events and Delegates and Its Respective Applications

Difference between events and delegates and its respective applications

From the technical standpoint, other answers have addressed the differences.

From a semantics perspective, events are actions raised by an object when certain conditions are met. For example, my Stock class has a property called Limit, and it raises an event when the stock prices reaches the Limit. This notification is done via an event. Whether anyone actually cares about this event and subscribes to it is beyond the concern of the owner class.

A delegate is a more generic term to describe a construct similar to a pointer in C/C++ terms. All delegates in .Net are multicast delegates. From a semantics perspective, they are generally used as a kind of input. In particular, they are a perfect way to implement the Strategy Pattern. For example, if I want to sort a List of objects, I can provide a Comparator strategy to the method to tell the implementation how to compare two objects.

I have used the two methods in production code. Tons of my data objects notify when certain properties are met. Most basic example, whenever a property changes, a PropertyChanged event is raised (see INotifyPropertyChanged interface). I have used delegates in code to provide different strategies of turning certain objects into string. This particular example was a glorified ToString() list of implementations for a particular object type to display it to users.

What are the differences between delegates and events?

An Event declaration adds a layer of abstraction and protection on the delegate instance. This protection prevents clients of the delegate from resetting the delegate and its invocation list and only allows adding or removing targets from the invocation list.

C# // Why use events and/or delegates?

Difference between delegates and events

So what’s really the difference between delegates and events other than the sugar coated syntax of events. The main difference is that event provides one more level of encapsulation over delegates.
So when we pass delegates it’s naked and the destination / subscriber can modify the delegate. When we use events the destination can only listen to it.

Summarizing Use of delegates

There are 6 important uses of delegates:-
1. Abstract and encapsulate a method (Anonymous invocation)
This is the most important use of delegates; it helps us to define an abstract pointer which can point to methods and functions. The same abstract delegate can be later used to point to that type of functions and methods. In the previous section we have shown a simple example of a maths class. Later addition of new algorithm functions does not affect the UI code.

1. Callback mechanismMany times we would like to provide a call back mechanism. Delegates can be passed to the destination and destination can use the same delegate pointer to make callbacks.

2. Asynchronous processingBy using ‘BeginInvoke’ and ‘EndInvoke’ we can call delegates asynchronously. In our previous section we have explained the same in detail.

3. Multicasting - Sequential processing Some time we would like to call some methods in a sequential manner which can be done by using multicast delegate. This is already explained in the multicast example shown above.

4. Events - Publisher subscriber modelWe can use events to create a pure publisher / subscriber model.

C# Event Implementation Fundamentals, Best Practices and Conventions

6 important uses of Delegates and Events

What is the use of Events when Delegates can do the job

They are essentially the same yes, but the simple difference is that delegates can be invoked from any scope (visibility permitting), but an event can only be invoked by a member on the class that declares it.

Do events create instance of the assigned delegate or it's just a convention?

According to Microsoft Docs => Here

An event is a special kind of multicast delegate that can only be invoked from within the class that it is declared in. Client code subscribes to the event by providing a reference to a method that should be invoked when the event is fired. These methods are added to the delegate's invocation list through event accessors.

So, the answer would be: Yes. Events are basically a special type of multicast delegate.

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