Delegates and Events

Delegates are the function to pointer. A delegate keeps the reference of function. Like as pointer in C/C++, same in C# we have delegates. Delegates in C# are reference types. They are type safe, managed function pointers in C# that can be used to invoke a method that the delegate refers to. The signature of the delegate should be the same as the signature of the method to which it refers.

The signature of a delegate type comprises of the following.

• The name of the delegate
• The arguments that the delegate would accept as parameters
• The return type of the delegate 

Let us see the working of delegates with this simple example. Here in this example, I am using a button click event. A message appears when the button is clicked.

Creation a button control can be seen below.

this.button1 = new System.Windows.Forms.Button();

this.SuspendLayout();

//

// button1

//

this.button1.Location = new System.Drawing.Point(93, 71);

this.button1.Name = "button1";

this.button1.Size = new System.Drawing.Size(75, 23);

this.button1.TabIndex = 0;

this.button1.Text = "button1";

this.button1.UseVisualStyleBackColor = true;

//Here we see that on clicking on button a Event Handler is calling named as  button1_click 
this.button1.Click += new System.EventHandler(this.button1_Click);

The form1.cs code is:

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

namespace AnApplicationOfDelagatesNEvent

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            MessageBox.Show("Hi this is  Button click event");

        }

        public void MyMessage( object sender , System.EventArgs e)

        {

            MessageBox.Show("Hi this from My Method");

        }

    }

}

Here on the button click event a message appears. Here I also write a method.

Here if user run the application and click on button then:

Figure 1.

Now I am calling MyMessage on the click of Button. Here we see that now if user click on button then the defination of button1_click will not be called because here Event is calling from MyMessage.

this.button1.Click += new System.EventHandler(MyMessage);



Figure 2.