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C# .Net Source Code for /Articles/ASP.NET/CreatingEventsCSharp.aspx

This ASP.NET page was written by Mike Gonzalez.
<% @ Page Language="C#" Debug="True" %>
<% @ Register TagPrefix="DotNetFun" TagName="Header" Src="/Header.ascx" %>
<% @ Register TagPrefix="DotNetFun" TagName="Footer" Src="/Footer.ascx" %>
<script language="C#" runat="Server">
	private void Page_Load() {
		ltrCategories.Text = CtrlHeader.ArticleCategory1 + "|" + CtrlHeader.ArticleCategory2 + "|" + 
			CtrlHeader.ArticleCategory3 + "|" + CtrlHeader.ArticleCategory4;
		ltrCategories.Text = DotNetFun.Common.AddCommas(ltrCategories.Text, '|');
	}
	private void Add_Click(Object source, EventArgs e) {
		try {
			MTG m = new MTG();
			// you can use the 'new' keyword to create an instance of a delegate (virtual method):
			m.NumberTooHighEvent += new MTG.NumberTooHighDelegate(MTG_NumberTooHigh);
			txtAns.Value = m.AddTwoNumbers(Convert.ToInt32(txtNum1.Value), 
				Convert.ToInt32(txtNum2.Value)).ToString();
		}
		catch (Exception err) {
			ltrStatus.Text = err.Message;
		}
	}
	// this is the Delegate method for the MTG.NumberTooHigh event:
	private void MTG_NumberTooHigh(int Number) {
		ltrStatus.Text = "The sum of two numbers provided exceeded 100!";
	}
	// this is the new test class for the event
	public class MTG {
		private int intA, intB;
		// note: both delegate and event declarations MUST be made public
		public delegate void NumberTooHighDelegate(int Number);
		// public event [Delegate Variable] [Event Variable];
		public event NumberTooHighDelegate NumberTooHighEvent;
		public int AddTwoNumbers(int Number1, int Number2) {
			if (Number1 + Number2 > 100) NumberTooHighEvent(Number1 + Number2);
			return Number1 + Number2;
		}
	}
</script>
<dotnetfun:header id="CtrlHeader" runat="Server" enableviewstate="False" allowrobotindex="true" pagetitle="Creating Events with C#" pagedescription="Learn how to define events in classes using C#." pagekeywords="c#, asp.net, event, delegate, .net, framework, class" authorname="Mike Gonzalez" authordate="1-2-2003" articlecategory1=".Net Framework" articlecategory2="C#" articlecategory3="ASP.NET" articlecategory4="Events" articletitle="Creating Events with C#" articledescription="Learn how to define events in classes using C#." allowviewsource="true"/>
<h2><font face="arial" color="darkblue">
	<%# CtrlHeader.ArticleTitle %>
</font></h2>
<font face="arial" size="2" color="darkblue">
	<b><%# CtrlHeader.ArticleDescription %></b><br/>
	<em>Category:</em> <asp:literal id="ltrCategories" runat="Server" enableviewstate="False"/> 
	<em>Posted</em> <%# CtrlHeader.AuthorDate.ToShortDateString() %>, 
	<em>By</em> <%# CtrlHeader.AuthorName %><br/>
</font>
<hr noshade="true" size="5" color="<%# CtrlHeader.SiteDataSet.Tables[0].Rows[0][" navbackgroundcolor"] %>" />
<table width="100%" bgcolor="#DDDDDD">
<form runat="Server">
<tr><th align="left" bgcolor="#FFFFDD"><font face="arial" size="2">C# Event Example:</font></th></tr>
<tr><td>
<font face="arial" size="2">
<b>Add two numbers here - if the answer is calculated to be over 100 an event will be fired.</b><br/>
<input type="text" size="5" id="txtNum1" runat="Server"/> + 
<input type="text" size="5" id="txtNum2" runat="Server"/> 
<input type="submit" value="=" runat="Server" onserverclick="Add_Click"/> 
<input type="text" size="5" id="txtAns" runat="Server" readonly="True"/>
<br/>
<font color="red"><asp:literal id="ltrStatus" runat="Server" enableviewstate="False"/></font>
</font>
</td></form></tr>
</table><br/><br/>
<font face="arial" size="2">
Events are defined as variables. When defining an event variable you must assosiate with it a delegate it can 
use to invoke a target method.<br/><br/>
<img src="images/EventDelegatesExampleDiagram.gif" border="0" alt="<%# CtrlHeader.ArticleTitle %> - Diagram Example"/><br/><br/>
<ol>
<li><b>Creating the delegate:</b>
<xmp style="background-color:#FFFFDD; font-size:10pt">
public delegate void NumberTooHighDelegate(int Number);
</xmp></li>
<li><b>Creating the event:</b>
<xmp style="background-color:#FFFFDD; font-size:10pt">
public event NumberTooHighDelegate NumberTooHighEvent;
</xmp></li>
<li><b>Raising the event:</b>
<xmp style="background-color:#FFFFDD; font-size:10pt">
NumberTooHighEvent(Number1 + Number2);
</xmp></li>
<li><b>Creating the delegate, creating the event and raising the event should be confined to a given class:</b>
<xmp style="background-color:#FFFFDD; font-size:10pt">
public class MTG {
	private int intA, intB;
	// note: both delegate and event declarations MUST be made public
	public delegate void NumberTooHighDelegate(int Number);
	// public event [Delegate Variable] [Event Variable];
	public event NumberTooHighDelegate NumberTooHighEvent;
	public int AddTwoNumbers(int Number1, int Number2) {
		if (Number1 + Number2 > 100) NumberTooHighEvent(Number1 + Number2);
		return Number1 + Number2;
	}
}
</xmp></li>
<li><b>Assigning an Event Handler to the event outside of the class/object:</b>
<xmp style="background-color:#FFFFDD; font-size:10pt">
// this is the event handler method that handles an HtmlInputInput ServerClick event in ASP.NET:
private void Add_Click(Object source, EventArgs e) {
	try {
		MTG m = new MTG();
		// you can use the 'new' keyword to create an instance 
		// of a delegate (virtual method):
		m.NumberTooHighEvent += new MTG.NumberTooHighDelegate(MTG_NumberTooHigh);
		txtAns.Value = m.AddTwoNumbers(Convert.ToInt32(txtNum1.Value), 
			Convert.ToInt32(txtNum2.Value)).ToString();
	}
	catch (Exception err) {
		ltrStatus.Text = err.Message;
	}
}
// this is the Delegate method for the MTG.NumberTooHigh event:
private void MTG_NumberTooHigh(int Number) {
	ltrStatus.Text = "The sum of two numbers provided exceeded 100!";
}
</xmp></li>
</ol>
</font>
<dotnetfun:footer id="CtrlFooter" runat="Server" enableviewstate="False"/>