What is Delegate? [closed]

Answer 1

A delegate is an object that can refer to a method. Thus, when we create a delegate, we are creating an object that can hold a reference to a method. Furthermore, the method can be called through this reference. Thus, a delegate can invoke the method to which it refers. The principal advantage of a delegate is that it allows us to specify a call to a method, but the method actually invoked is determined at runtime, not at compile time.

Simple Delegate

Declaration of delegate:
delegate-modifier delegate return-type delegate-name(parameters)
Implementation of delegate:
Delegate-name delegate-object=new Delegate-name(method of class)

http://knowpacific.wordpress.com/2012/01/26/delegate/

Answer 2

A great explanation and practical implementation of the Delegate pattern can be found in the Google Collections Forwarding Classes (also, the Decorator pattern).

Answer 3

In Event communication sender does not know which object will handle the event. Delegate is type which hold the reference of method. Delegate has signature and holds reference to method which matches its signature so Delegate is like type safe function pointer.

button1.Click += new System.EventHandler(button1_Click) System.EventHandler is declared as a delegate here In .net Events work on the concept of Delegate (like Button Click)

Delegate is used when you do not know which code to invoke at run time So at that time Delegate is used to handle Events

http://msdn.microsoft.com/en-us/library/ms173171(v=vs.80).aspx

Answer 4

A delegate is an object that represents a pointer to a function. However, it is not an ordinary function pointer in that it:

1) Is Object Oriented

2) Is type safe, i.e. it can only point to a method and you cannot read the raw memory address it is pointing to

3) Is strongly typed. It can only point to methods that match its signatures.

4) Can point to more than one method at the same time.

Answer 5

a delegate is simply a function pointer.
simply put you assign the method you wish to run your delegate. then later in code you can call that method via Invoke.

some code to demonstrate (wrote this from memory so syntax may be off)

delegate void delMyDelegate(object o);

private void MethodToExecute1(object o)
{
    // do something with object
}

private void MethodToExecute2(object o)
{
    // do something else with object
}

private void DoSomethingToList(delMyDelegate methodToRun)
{
    foreach(object o in myList)
        methodToRun.Invoke(o);
}

public void ApplyMethodsToList()
{
    DoSomethingToList(MethodToExecute1);
    DoSomethingToList(MethodToExecute2);
}

Answer 6

Taken from here

Q What are delegates?
A When an object receives a request, the object can either handle the request itself or pass the request on to a second object to do the work. If the object decides to pass the request on, you say that the object has forwarded responsibility for handling the request to the second object.

Or, as an easy pseudo example: something sends a request to object1. object1 then forwards the request and itself to object2 -- the delegate. object2 processes the request and does some work. (note: link above gives good examples)