Understading Delegates

What are delegates?
Delegates are object that refer to an method. Normally we refer to objects, however referring to an object isn’t any different from referring a method they too have physical location in memory.

Why use delegate?
One delegate can be used to call different methods during runtime of a program by simply changing the method to which the delegate refers.
and Delegates Support Events.

delegate ret-type name(paramerter-list);
e.g. delegate string MyDelegate();

The MyDelegate can call any method whose return type is string and accepts no parameter. It can be instance method or a static method.

delegate string MyDelegate(String s);
class Program
{
static string GetNameLower(String s)
{
return s.ToLower() ;
}
static string GetNameUpper(string s)
{
return s.ToUpper();
}
static void Main(string[] args)
{
MyDelegate myD = new MyDelegate(GetNameLower); //or myD=GetNameLower
string s1 = myD(“Hi Nishant”);
Console.WriteLine(s1);
myD = new MyDelegate(GetNameUpper); //or myD=GetNameUpper
string s2 = myD(“Hi Nishant”);
Console.WriteLine(s2);
}
}

Understanding Multicasting

We can have chain of methods that will be called automatically when a delegate is invoked.
For this we will use += operator to add methods to chain and -= to remvove a method.
If delegate returns value than value returned by the last method becomes the return value of entire deleagation invocation. Thus a delegate making use of multicasting will have void as return type.

delegate void MyDelegate();
class Program
{
static void GetNameLower()
{
Console.WriteLine(“GetNameLower Called”);
}
static void GetNameUpper()
{
Console.WriteLine(“GetNameUpper Called”);
}
static void Main(string[] args)
{
MyDelegate myD = GetNameLower;
myD +=GetNameUpper;
myD(); //invoking the delegate
}