what is Delegate?
A delegate is a type that references a method. Once a delegate is assigned a method, it behaves exactly like that method. The delegate method can be used like any other method, with parameters and a return value, as in this example:
Example:
public delegate int PerformCalculation(int x, int y);
Delegates have the following properties:
- Delegates are similar to C++ function pointers, but are type safe.
- Delegates allow methods to be passed as parameters.
- Delegates can be used to define callback methods.
- Delegates can be chained together; for example, multiple methods can be called on a single event.
- Methods don't need to match the delegate signature exactly. For more information, see Covariance and Contravariance
- C# version 2.0 introduces the concept of Anonymous Methods, which permit code blocks to be passed as parameters in place of a separately defined method.
Sample for Delegate
delegate void Del(string s);
class TestClass
{
static void Hello(string s)
{
System.Console.WriteLine(" Hello, {0}!", s);
}
static void Goodbye(string s)
{
System.Console.WriteLine(" Goodbye, {0}!", s);
}
static void Main()
{
Del a, b, c, d;
// Create the delegate object a that references
// the method Hello:
a = Hello;
// Create the delegate object b that references
// the method Goodbye:
b = Goodbye;
// The two delegates, a and b, are composed to form c:
c = a + b;
// Remove a from the composed delegate, leaving d,
// which calls only the method Goodbye:
d = c - a;
System.Console.WriteLine("Invoking delegate a:");
a("A");
System.Console.WriteLine("Invoking delegate b:");
b("B");
System.Console.WriteLine("Invoking delegate c:");
c("C");
System.Console.WriteLine("Invoking delegate d:");
d("D");
}
}
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