Simple and Multicast Delegate in C#

A useful property of delegate objects is that multiple objects can be assigned to one delegate instance by using the + operator. The multicast delegate contains a list of the assigned delegates. When the multicast delegate is called, it invokes the delegates in the list, in order. Only delegates of the same type can be combined.

The "-" operator can be used to remove a component delegate from a multicast delegate.

1. Open Visual Studio go to>>File>>New>>Website>>Asp.net Empty Website and name anything but named DelegatesExplained:

2. Add New WebForm to your Project and Name DelegateExplained.aspx,you can name anything:

3. Add the following under the body tag of Desing page of DelegatesExplained.aspx:

<form id="form1" runat="server">
<div>
<asp:Label ID="Label1" runat="server"></asp:Label>
<asp:Label ID="Label2" runat="server"></asp:Label>
<asp:Label ID="Label3" runat="server"></asp:Label>
</div>
</form>

4. Now open .DelegatedExplained.cs and define the delegate name Delegates:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public delegate void Delegates();

5. Create three functions name First,Second and Third outside the pageload() function:

protected void Page_Load(object sender, EventArgs e)
{
}
public void First()
{
Label1.Text = "First";
}
public void Second()
{
Label2.Text = "Second";
}
public void Third()
{
Label3.Text = "Third";
}

6. Create Objects Of Delegate under pageload() method:

protected void Page_Load(object sender, EventArgs e)
{
MultipleDelegate m1,m2,m3;
}
public void First()
{
Label1.Text = "First";
}
public void Second()
{
Label2.Text = "Second";
}
public void Third()
{
Label3.Text = "Third";
}

7. Now add refrence of Function name First() to m1 and calling the function by calling m1():

protected void Page_Load(object sender, EventArgs e)
{
MultipleDelegate m1;
m1 = First; //adding reference to the First Function
m2=Second; //adding reference to the SecondFunction
m3=Third; //adding reference to the Third Function
m1();
m2();
m3();
}
public void First()
{
Label1.Text = "First";
}
public void Second()
{
Label2.Text = "Second";
}
public void Third()
{
Label3.Text = "Third";
}

Now run by pressing ctrl+f5;

Now see output will be:

Now Multicast Delegates by using + operator rather then calling each object separately create a new object m4 and add all the delegates objects in it.

Only delegates of the same type can be combined.

protected void Page_Load(object sender, EventArgs e)
{
MultipleDelegate m1, m2, m3,m4;
m1 = First; //adding reference to the First Function
m2 = Second; //adding reference to the SecondFunction
m3 = Third; //adding reference to the Third Function
m4 = m1 + m2 + m3; //casting all three objects of MuticastDelegate to one object;
m4();
}
public void First()
{
Label1.Text = "First";
}
public void Second()
{
Label2.Text = "Second";
}
public void Third()
{
Label3.Text = "Third";
}

Now see output will be the same:

You Can also use the "-" operator to remove any object as given below:

Create new object m5:

protected void Page_Load(object sender, EventArgs e)
{
MultipleDelegate m1, m2, m3,m4,m5;
m1 = First; //adding reference to the First Function
m2 = Second; //adding reference to the SecondFunction
m3 = Third; //adding reference to the Third Function
m4 = m1 + m2 + m3; //casting all three objects of MuticastDelegate to one object;
m5 = m4 - m3;
m5();
}
public void First()
{
Label1.Text = "First";
}
public void Second()
{
Label2.Text = "Second";
}
public void Third()
{
Label3.Text = "Third";
}

Now output will change and show only two functions: First and Second:

Thanks.