Sunday, May 1, 2011 user control raise event parent form

Before I get into this topic, lets look at a few definitions

Event: An event in C# is an occurrence. For example if you click a button, that is a button click event.

Subscribing to an Event: Stating which method needs to be called when an event occurs

Event Handler: The method that will be executed when an event occurs (or raised).

Delegate: Delegate is a function pointer. Check this out for a discussion on delegates.

How to subscribe to an event

If you want to subscribe to the SelectedIndexChanged event of a dropdown (ddlDept) in the code behind, this is the syntax to do it

ddlDept.SelectedIndexChanged+=new EventHandler(ddlDept_SelectedIndexChanged);

In the line of code above:

What it means

The event that you are subscribing to
A delegate that is defined in the .net framework
The name of the method  (or function) you want to call when the event occurs

This is the general syntax for consuming any event

EventName+=new DelegateName(MethodName)

The publisher defines the delegate and the event. The subscriber, defines the event handler (a method).

How to create and raise an event and consume it somewhere else

Suppose you have a user control. In this user control you want to raise an event on a button click,  which you want to handle in the page containing the user control. This is a way to do it.

This is your code in the usercontrol ascx (Publisher)

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="MyUserControl.ascx.cs" Inherits="MyUserControl" %>

<asp:Button ID="Button1" runat="server" Text="ClickMe"
    onclick="Button1_Click"  />

The code behind for the user control

using System;
using System.Web;

public partial class MyUserControl : System.Web.UI.UserControl
    //Define the delagate (The method handling this event would need to have the same signature)
    public delegate void myDelegate(string s);

    //Define the event that needs to be raised
    public event myDelegate myEvent;

    protected void Page_Load(object sender, EventArgs e)
    protected void Button1_Click(object sender, EventArgs e)
        if (myEvent!=null)
           string s = "Hello from usercontrol!";

           //The event myEvent is raised in the next line

The aspx page that holds user control (Subscriber)

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>
<%@ Register Src="~/MyUserControl.ascx" TagPrefix="UserControl" TagName="EventEg" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "">

<html xmlns="">
<head runat="server">
    <title>Event example</title>
    <form id="form1" runat="server">
    <UserControl:EventEg id="ucEventEg" runat="server" />

The code behind for the aspx

 using System;

public partial class _Default : System.Web.UI.Page

    protected void Page_Load(object sender, EventArgs e)
        //Subscribe to the user control's event named myEvent
        ucEventEg.myEvent += new MyUserControl.myDelegate(UserCortolButtonClicked);


    private void UserCortolButtonClicked(string s)

When you run the web application, this is how the page would look like

When you click the button this is what happens

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