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.Net Delegates

Delegates, Anonymous Delegates, Lambdas, 

This article (part1) forms part of a mini series which will

 and Generics

What is a Delegate?

You may be wondering why another article on delegates. If you are already comfortable using them, maybe you are done here, or maybe you have the job of mentoring other developers in your team and have found it tricky to explain in the real world, or maybe you have sat down with a team member and they still don't really get them. On my travels i frequently meet developers who failed to really grasp delegates earlier on and thus struggle with many other topics which build on a solid understanding of what delegates are. For example: Lambda Expressions, Reading and Writing queries targeted at LINQ to EntitiesEvents and Generics to name a few.

If we search MSDN the definition we find is as follows
delegate is a reference type that can be used to encapsulate a named or an anonymous method. Delegates are similar to function pointers in C++; however, delegates are type-safe and secure.

You may come from a C++ background like myself in which case function pointers were an essential part of calling libraries from third party vendors and frameworks to get hold of OS information and tooling. However if not, it may take a while and some understanding of what problems are solved through using delegates to really start using them day to day and at which point they will become second nature.

This article, Part 1, aims to form a series of articles with source code that will build on top of one another to progressively build the delegate story...

Can i ask again, What is a Delegate?

My first answer would be "You can think of a delegate as an object that holds one or more methods".
 Normally we don't just go ahead and execute an object, but rather we do the following:

  • Declare the type
  • Declare a variable of the type
  • Instantiate the variable and set properties
  • Use the variable
//Declare the type
public class Car
{
private int speed = 0;

public string Make{get;set;}
public string Model{get;set;}

public void Accelerate()
 {
  speed = 210
 }
}

//Declare a variable of the type
Car fastCar;

//Instantiate the variable and set properties
fastCar = new Car(){ Make = "Porshe", Model = "950" };

//Use the variable
fastCar.Accelerate();


A delegate is a type that has already been created by the .Net team.
For a delegate we do something similar:

  • Declare the delegate type
  • Declare a variable of the delegate type
  • Create an instance of the delegate and set it's reference 



A delegate is already a type that is part of the .Net framework class library



Multicast

Every delegate is a 'multicast delegate', which means each delegate maintains an invocation list of all the methods it needs to invoke when the delegate itself is invoked or called.


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