What is a Delegate?
In the English language one of the meanings of a delegate is "To commit or entrust to another". Thats precisely what a delegate does in C#. When called, it entrusts (delegates) the job to another method (function). If you are coming from the C++ world, you must note that in C++ delegate is implemented as a function pointer, but C# it is implemented as a class.
In the example below I define a delegate. Then I use instances of that delegate to call two different methods.
One important thing to remember about delegates is that, it can be passed as a parameter (which you cannot do with methods)
Using Delegate as a parameter to a method
Using Delegate to create an anonymous method
Anonymous method is a shorthand way to assign a method to a delegate without having to declare a method separately. Anonymous method is an important (but simple) concept to be learned before you can learn Lambda expressions.
In this example below, instead of separately creating an add method, I will directly declare it when I instantiate the delegate.
In the English language one of the meanings of a delegate is "To commit or entrust to another". Thats precisely what a delegate does in C#. When called, it entrusts (delegates) the job to another method (function). If you are coming from the C++ world, you must note that in C++ delegate is implemented as a function pointer, but C# it is implemented as a class.
In the example below I define a delegate. Then I use instances of that delegate to call two different methods.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace DelegateExample
{
class Program
{
/*DECLARE THE DELEGATE WITH THE SAME SIGNATURE AS THE FUNCTION TO BE CALLED*/
delegate void myDelegate();
static void Main(string[] args)
{
/*INSTANTIATE THE DELEGATE INSTANCE TO THE FUNCTION THAT NEEDS TO BE CALLED*/
myDelegate myDel1= SayHello;
myDelegate myDel2 = SayGoodBye;
myDel1();
//Displays Hello!
myDel2();
//Displays Bye!
}
private static void SayHello()
{
Console.WriteLine("Hello!");
}
private static void SayGoodBye()
{
Console.WriteLine("Bye!");
}
}
}
Output window
One important thing to remember about delegates is that, it can be passed as a parameter (which you cannot do with methods)
Using Delegate as a parameter to a method
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Delagate
{
class Program
{
delegate int myDelegate(int x, int y);
static void Main(string[] args)
{
int a = 2;
int b = 3;
bool doYouWantToAdd = false;
myDelegate myDel;
if (doYouWantToAdd == true)
{
myDel = Add;
}
else
{
myDel = Subtract;
}
int z = AddOrSubtract(myDel, a, b);
Console.WriteLine(z);
}
static int Add(int a, int b)
{
return (a + b);
}
static int Subtract(int a, int b)
{
return (a - b);
}
static int
AddOrSubtract(myDelegate myDel, int a, int b)
{
//This method accepts a delegate as a parameter
return myDel(a, b);
}
}
}
Using Delegate to create an anonymous method
Anonymous method is a shorthand way to assign a method to a delegate without having to declare a method separately. Anonymous method is an important (but simple) concept to be learned before you can learn Lambda expressions.
In this example below, instead of separately creating an add method, I will directly declare it when I instantiate the delegate.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace DelegateExample
{
class Program
{
delegate int myDelegate(int a,int b);
static void Main(string[] args)
{
myDelegate myDel1 = new
myDelegate(delegate(int a, int b) { return (a + b); });//the
add method is an anonymous method here
int addResult=myDel1(1, 2);
Console.WriteLine(addResult);//displays 3
}
}
}
