Named Delegates in C#

Vijay Prativadi
Mar 10, 2013
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Introduction

This article demonstrates an interesting and very useful concept in C#.

Question: What are named delegates?

In simple terms "Delegates that are associated with a named method, where the method can be used at an invocation point by passing respective input parameters to obtain an expected result".

Step 1: Create a new web application

Step 2: Add a new Addition class

Step 3: The complete code of Addition.cs is as in the following:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
namespace NamedDelegatesApp
{
    public class Addition
    {
        public double Add(double a, double b)
        {
            return a + b;
        }
    }
}

Step 4: The complete code of WebForm1.aspx is as in the following:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="NamedDelegatesApp.WebForm1" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
        <center>
            <div>
                <table>
                    <tr>
                        <td colspan="2" align="center">
                            <asp:label id="Label1" runat="server" text="Named Delegates" font-bold="true" font-size="Large" font-names="Verdana" forecolor="Maroon"></asp:label>
                        </td>
                    </tr>
                    <tr>
                        <td>
                            <asp:label id="Label6" runat="server" text="Please Enter FirstNumber" font-size="Large" font-names="Verdana" font-italic="true"></asp:label>
                        </td>
                        <td>
                            <asp:textbox id="TextBox4" runat="server"></asp:textbox>
                        </td>
                    </tr>
                    <tr>
                        <td>
                            <asp:label id="Label2" runat="server" text="Please Enter SecondNumber" font-size="Large" font-names="Verdana" font-italic="true"></asp:label>
                        </td>
                        <td>
                            <asp:textbox id="TextBox1" runat="server"></asp:textbox>
                        </td>
                    </tr>
                    <tr>
                        <td colspan="2" align="center">
                            <asp:button id="Button1" runat="server" text="Addition" font-names="Verdana" width="213px" backcolor="Orange" font-bold="True" onclick="Button1_Click" />
                        </td>
                    </tr>
                    <tr>
                        <td colspan="2" align="center">
                            <asp:label id="Label5" runat="server" font-bold="true" font-names="Verdana"></asp:label>
                        </td>
                    </tr>
                </table>
            </div>
        </center>
    </form>
</body>
</html>

Step 5: The complete code of WebForm1.aspx.cs is as in the following:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace NamedDelegatesApp
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e){ }
        public delegate double namedDelegate(double a, double b);
        protected void Button1_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(TextBox4.Text) || string.IsNullOrEmpty(TextBox1.Text))
            {
                Label5.Text = "Please Enter Some Values";
                Label5.ForeColor = System.Drawing.Color.Red;
            }
            else
            {
                namedDelegate namedDel = objAddition.Add;
                Label5.Text = "Addition Result is: " + namedDel(double.Parse(TextBox4.Text), double.Parse(TextBox1.Text));
                Label5.ForeColor = System.Drawing.Color.Green;
                TextBox4.Text = string.Empty;
                TextBox1.Text = string.Empty;
            }
        }
        #region Instance MembersAddition objAddition = new Addition();
        #endregion
    }
}

Step 6: The output of the application is as in the following:

Step 7: The addition data output of the application is as in the following:

I hope this article was useful for you.