Delegates in c#

C# > Delegate

A delegate in C# is similar to a function pointer in C++. This allows encapsulating a reference to a method inside a delegate object.

A delegate is a type that defines a method signature. When you instantiate a delegate, you can associate its instance with any method with a compatible signature. You can invoke (or call) the method through the delegate instance.

An interesting and useful property of a delegate is that it does not know or care about the class of the object that it references

Delegates are especially used for implementing events and the call-back methods.

1. Basic delegate example

// declaration

        private delegate void TestDelegate();

        private  void StartTestDelegate()

        {
            MessageBox.Show("StartTestDelegate"); 
        }
        private void StopTestDelegate()
        {
            MessageBox.Show("StopTestDelegate");
        }

// Instantiation

        TestDelegate del1 = new TestDelegate(StartTestDelegate);
        TestDelegate del2 = new TestDelegate(StopTestDelegate);

// Invocation

        del1();
        del2();

2. Math Operator delegate example

  private class Math

  {
            public int Add(int x, int y)
            {
                return x + y;
            }
            public int Sub(int x, int y)
            {
                return x - y;
            }
            public MathDelegate Operator(int op) 
            {
                MathDelegate objDelegateMath = null;  // delegate reference
                if (op == 1)
                    objDelegateMath = Add;  // point the reference to methods
                else
                    objDelegateMath = Sub;  // point the reference to methods
               return objDelegateMath; 
            }
  }

  Math objMath = new Math();

  //Invoke the methods through delegate
  MessageBox.Show(objMath.Operator(1).Invoke(1, 2).ToString());
  MessageBox.Show(objMath.Operator(2).Invoke(5, 4).ToString()); 

3. Logger class delegate example 

Multicast delegates >>