Create and Use Application Level Events in ASP.NET


Introduction

The Global.asax, also known as the ASP.NET application file, is located in the root directory of an ASP.NET application. This file contains code that is executed in response to application-level and session-level events raised by ASP.NET or by HTTP modules. You can also define ‘objects’ with application-wide or session-wide scope in the Global.asax file. These events and objects declared in the Global.asax are applied to all resources in that web application. The Global.asax is an optional file. If a user requests the Global.asax file, the request is rejected. 

About Global.asax page

Adding a Global.asax to your web project is quiet simple. Open Visual Studio 2005 or 2008 > Create a new website > Go to the Solution Explorer > Add New Item > Global Application Class > Add.
Now we will have three Application Event Handlers and two Session Event Handlers.

Here is the list of Application Event Handlers:

Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
' Code that runs on application startup
End Sub
   
Sub Application_End(ByVal sender As Object, ByVal e As EventArgs)
' Code that runs on application shutdown
End Sub
       
Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
' Code that runs when an unhandled error occurs
End Sub


Here is the list of Session Event Handlers:


Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs)
' Code that runs when a new session is started
End Sub

Sub Session_End(ByVal sender As Object, ByVal e As EventArgs)
' Code that runs when a session ends.
' Note: The Session_End event is raised only when the sessionstate mode
' is set to InProc in the Web.config file. If session mode is set to StateServer
' or SQLServer, the event is not raised.
End Sub


Note: About Session Event Handlers will learn in next article.

Application Event Handlers
Application_Start(): It gets fired when the first resource is requested from the web server and the web application starts. Application_End(): It gets fired when the web application ends. Application_Error(): It gets fired when an error occurs.

Working with Global.asax file:

<%@ Application Language="VB" %>
<script runat="server">
    Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
        Application("HitCount") = 0
        ' Code that runs on application startup
    End Sub
   
    Sub Application_End(ByVal sender As Object, ByVal e As EventArgs)
        ' Code that runs on application shutdown
    End Sub
       
    Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
        ' Code that runs when an unhandled error occurs
    End Sub

    Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Code that runs when a new session is started
    End Sub

    Sub Session_End(ByVal sender As Object, ByVal e As EventArgs)
        ' Code that runs when a session ends.
        ' Note: The Session_End event is raised only when the sessionstate mode
        ' is set to InProc in the Web.config file. If session mode is set to StateServer
        ' or SQLServer, the event is not raised.
    End Sub 
</script>

Working with Default.aspx file:

<%@ Page Language="VB" AutoEventWireup="false"
CodeFile="Default.aspx.vb" Inherits="_Default" %>

<!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 runat="server">
    <title>Create and Use Application Level Events in ASP.Net</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <strong>
        Total Hits:
        </strong>
        <asp:Label ID="Label1" runat="server"
Text="Label" Width="247px" Font-Size="Large" ForeColor="Red">
        </asp:Label>
    </div>
    </form>
</body>
</html>

Working with Default.aspx.vb file:

Protected Sub Page_Load(ByVal sender As Object,
ByVal e As System.EventArgs) Handles Me.Load
        Application("HitCount") = Application("HitCount")   1
        Label1.Text = Application("HitCount")
End Sub

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