Practical Use of Delegate in real time Application -1

Introduction

Many time we get questions like where can we use delegate ?  Give us a practical example .In fact I saw 2-3 similar questions in this forum so thought of writing this article.

In this age programmers are more interested in building dynamic and reusable component. There are scenarios where a normal function will not help to fulfil the purpose. Below are two important features in delegate which helps to make a component dynamic.

1-      1. It allows to inject code by the client(I will describe in this article)

2-      2. Multi-casting (I will describe in the next article)

Inject functions by client code.

Ok let's do a practical  example to make it clear. One important use of delegate is with the help of delegate  we can develop a component which client can use and inject their functionality to it. In the below example I have shown a UserRegistration Component. Client will call this component to register a user ,however it entirely depends on the client  to implement how they want to notify users about their registration via email or via SMS .

namespace RegistrationModule

{ 

    public delegate void NotifyUser(ContactDetail objContact); 

    class RegisterUser
    {

        public void Register(Userinfo objUser, NotifyUser myFunc)
        {

            //code to save the user details to the database

            // 

            myFunc(objUser.objContact);

        } 

    }

    class Userinfo
    {

        public string name;
        public int age;
        public ContactDetail objContact;
    }

    class ContactDetail
    {

        public string email;
        public string mobNo;
    }

}

Client Code:

Lets say first client wants to send SMS to notify their user.So below will be their implementation.

I have given the comment to explain the code.

//Below function is having same signature as delegate NotifyUser and will be attached to the delegate.
public void SendSMS(ContactDetail objContact)

        {

            string MobNo = objContact.mobNo;
            //Add your code to send Registration success message to the user mobile number.

        }

        public void RegisterUser()

        {
  //Create an Object of Userifo and fill the user details to it.
            Userinfo obj = new Userinfo();           

            obj.name = "Satya Sahoo";

            obj.age = 29;

            ContactDetail objC = new ContactDetail();

            objC.mobNo = "977788888";

            objC.email = "esensahoo@sweetcrazyboy.net";

            obj.objContact = objC;

   //Create a delegate instance and attach the SendSMS() to it.
            NotifyUser sendSMS = new NotifyUser(SendSMS);

            RegisterUser objReg = new RegisterUser();

//Invoke the register function with the Delegate Instance sendSMS

            objReg.Register(obj, sendSMS); 

        }

Now lets say the second client wants to notify the user via email:

public void SendEmail(ContactDetail objContact)

        {
            string strEmail = objContact. email;

            //Add your code to send Registration success email to the user email address.

        }

        public void RegisterUser()

        {

            Userinfo obj = new Userinfo();           

            obj.name = "Satya Sahoo";

            obj.age = 29;

            ContactDetail objC = new ContactDetail();

            objC.mobNo = "977788888";

            objC.email = "esensahoo@sweetcrazyboy.net";

            obj.objContact = objC; 

            NotifyUser sendEmail = new NotifyUser(SendEmail); 

            RegisterUser objReg = new RegisterUser();

            objReg.Register(obj, sendEmail);

         }

That's it.Now client-1 user will get user registration success message as an SMS and client-2 will get user registration success message as an email.  Important thing to notice here is SendSMS and SendEmail is the code written by the client however it is invoked by the RegistrationModule what in other words we can say delegates allow us to inject functionality.

Conclusion