Delegate in C# Part 1 (Single cast delegate and Multicast delegate)

                

                This Article will give you brief description about delegate and its types; a delegate in C# is similar to a function pointer in C or C++. Unlike function pointers in C or C++, delegates are object-oriented, type-safe, and secure.

There are three steps in defining and using delegates:

1. Declaration

2. Instantiation and

3. Invocation

Delegate declaration:

          Declaration is done with keyword delegate, followed by return type, delegate name and parameters (optional).

public delegate void mydelegate(int x, int y);

Delegate Instantiation:

        It’s nothing but creating object for delegate and assigning function to it. There are different ways to instantiate delegate

        mydelegate del = new mydelegate(Add);

Or

        mydelegate del = Add;

Note:

                The function should have same return type (above one is void), with same parameter type and numbers, otherwise compiler will through error.

Delegate Invocation:

                Calling methods associate with the delegate is delegate invocation; it can be synchronous or asynchronous.

1. Synchronous invocation:

                It waits for the method to complete its execution, and then goes to next statement, why because it’s maintained in single thread.

                del(5,10);            

Or

del.Invoke(10, 10);

2. Asynchronous invocation:

                It won’t wait for the associated method to complete its execution; the method execution is maintained in separate thread, once the process complete it will return to Targetmethod.

del.BeginInvoke(5,10,new AsyncCallback(Targetmethod),null)

       The target method should have IAsyncResult as parameter 

 Based on method(s) associate with delegate, it’s classified into two types

1. Singlecast delegate

2. Multicast delegate

1. Single cast Delegate:

                Singlecast delegates provide functionality to execute only one method with or without return type.

Example:

            public delegate string SingleCastDelegate(string first,string second);

The function associated with single cast delegate is,

public string AddString(string firstName, string secondName)

        {

            return string.Concat(firstName, secondName);

        }

2. Multicast Delegate:

                Delegate who refers to more than one function is multicast delegate, unlike single cast delegate; there are some restrictions in multicast delegate.

Restriction:

                1.  Return type of multicast delegate is always void, because it involves more than one function.

                2. It’s always called in the order, which is assigned to it, for example its assigned in order like a(), b(), c() means it’s called in same order.

Example:

                I’m having four function Add, Difference, Product, Division, now I’m going to add all this four functions to my delegate, make sure that it follows same signature as delegate

//Multicast delegate

        public delegate void MultiCastDelegateCalculator(int x, int y);

//Adding functions to delegate

MultiCastDelegateCalculator delMulti =new MultiCastDelegateCalculator(calc.Add);

delMulti += calc.Difference;

            delMulti += calc.Product;

            delMulti += calc.Division;

            delMulti(5, 10);

And finally invoke the delegate with some input.

       We can also remove function from delegate if it’s not needed, to remove function from delegate replace + with -.

            delMulti -= calc.Product;

            delMulti(5, 10);

       Now the function Product will no longer available in delegate.

Attachment:

       I enclose sample project for the understanding of single cast and multicast delegate.

Download Delegate Sample