Reverse AJAX technique in ASP.NET (VBASPNETReverseAJAX)

Reverse Ajax is also known as Comet Ajax, Ajax Push, Two-way-web and HTTP server push. This technique persists a HTTP request to allow the server push data to a browser, without requesting the server in a individual time. This sample shows how to use thi

VB.NET (61.5 KB)
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'****************************** Module Header ******************************\
' Module Name:    Receiver.aspx.vb
' Project:        VBASPNETReverseAJAX
' Copyright (c) Microsoft Corporation
' The user will use this page to log in with a unique user name. Then when there is a 
' new message on the server, the server will immediately push the message to the client.
' This source is subject to the Microsoft Public License.
' See
' All other rights reserved.

Partial Public Class Receiver
    Inherits System.Web.UI.Page
    Protected Sub btnLogin_Click(ByVal sender As Object, ByVal e As EventArgs)
        Dim userName As String = tbUserName.Text.Trim()

        ' Join into the recipient list.
        If Not String.IsNullOrEmpty(userName) Then

            Session("userName") = userName
        End If
    End Sub

    Protected Sub Page_PreRender(ByVal sender As Object, ByVal e As EventArgs)
        ' Activate the JavaScript waiting loop.
        If Session("userName") IsNot Nothing Then
            Dim userName As String = DirectCast(Session("userName"), String)

            ' Call JavaScript method waitEvent to start the wait loop.
            ClientScript.RegisterStartupScript(Me.[GetType](), "ActivateWaitingLoop", "waitEvent();", True)

            lbNotification.Text = String.Format("Your user name is <b>{0}</b>. It is waiting for new message now.", userName)

            ' Disable the login.
            tbUserName.Visible = False
            btnLogin.Visible = False
        End If
    End Sub
End Class