Tutorial: Introduction to AJAX in ASP.NET 2.0 and VB
 
| Tutorial: Introduction to AJAX in ASP.NET 2.0 and VB |
AJAX, short for Asynchronous JavaScript And XML, isn't a technology but rather a grouping of technologies. AJAX uses a communication technology (typically SOAP and XML) to send and receive an asynchronous request/response to the server, and then leverages presentation technologies (JavaScript, DOM, HTML, and CSS) to process the response. Applications using AJAX are legitimate today, because most browsers support the necessary technology.
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First thing we need to do is to import the AJAX namespace from Ajax.DLL.The Ajax namespace contains Ajax.dll encapsule Asynchronous Javascript and XML in Bin folder. This is an combination of Javascript and XML. The data is transfered in the form of XML.
Imports Ajax
Imports System.Data.SqlClient
Imports System.Data |
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In this tutorial, the only configuration step beyond that is to add the following code in the web.config file, inside the <system.web> element.
| <httpHandlers>
<add verb="POST,GET" path="ajax/*.ashx" type="Ajax.PageHandlerFactory, Ajax"/>
</httpHandlers> |
In order to make server-side functions available through JavaScript, two things must be done. First, the function or functions in question must be marked with the Ajax.AjaxMethodAttribute. Second, the class containing these functions must be registered through a call to Ajax.Utility.RegisterTypeForAjax during the page load event. Then we use GetData() even of btnGetData and display() event of DropDownList to do the work. The button btnGetData is a html button. It display employee data without page post-back. When chose a particular record in the Dropdownlist, the employee name and employee ID will be displayed in the label.
The code below can go in the <head> tags of the ASPX page:
<script language="javascript" type="text/javascript">
function GetData()
{
var response;
Ajax_CSharp.GetData(GetData_CallBack);
}
function GetData_CallBack(response)
{
var response=response.value;
if(response=="Empty")
{
alert("No Record Found !!!");
}
else if(response=='Error')
{
alert("An Error occured in accessing the DataBase !!!");
}
else
{
var arr=response.split("~");
var empID=arr[0].split(",");
var empName=arr[1].split(",");
document.getElementById('dlistEmployee').length=0;
for(var i=0;i<empID.length;i++)
{
var o = document.createElement("option");
o.value = empID[i];
o.text = empName[i];
document.getElementById('dlistEmployee').add(o);
}
}
function display()
{
var selIndex=document.getElementById("dlistEmployee").selectedIndex;
var empName=document.getElementById("dlistEmployee").options(selIndex).text;
var empID=document.getElementById("dlistEmployee").options(selIndex).value;
document.getElementById("lblResult").innerHTML="You have selected " + empName + " ( ID : " + empID + " )";
}
</script> |
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The front end AjaxDataSearchVB.aspx page looks something like this:
<div align="center">
<input id="btnGetData" onclick="GetData();" type="button" value="To Get Employee Data From DB" style="width: 203px" />
<asp:DropDownList ID="dlistEmployee" runat="server" onchange="display();">
</asp:DropDownList><asp:Label ID="lblResult" runat="server" Text="No Record Selected"></asp:Label> |
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Register Ajax in PageLoad and get data from the employee table of Database.
| Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
Ajax.Utility.RegisterTypeForAjax(GetType(Ajax_CSharp))
End Sub
<Ajax.AjaxMethod(HttpSessionStateRequirement.ReadWrite)> _
Public Function GetData() As String
Try
Dim con As New SqlConnection(ConfigurationManager.AppSettings("conn"))
Dim cmd As New SqlCommand("SELECT * FROM employee", con)
cmd.Connection.Open()
Dim adapter As New SqlDataAdapter(cmd)
Dim ds As New DataSet("DataSet")
adapter.Fill(ds, "Table")
If ds.Tables(0).Rows.Count <= 0 Then
Return "Empty"
Else
Dim empID As String = ""
Dim empName As String = ""
Dim i As Integer
For i = 0 To ds.Tables(0).Rows.Count - 1
empID += ds.Tables(0).Rows(i)(0).ToString() + ","
empName += ds.Tables(0).Rows(i)(1).ToString() + ","
Next i
empID = empID.Substring(0, empID.Length - 1)
empName = empName.Substring(0, empName.Length - 1)
Return empID + "~" + empName
End If
Catch
Return "Error"
End Try |
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The flow for the code behind page is as follows.
Imports System
Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
Imports System.Collections
Imports System.Web
Imports System.Web.Security
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.WebControls.WebParts
Imports System.Web.UI.HtmlControls
Imports Ajax
Class Ajax_CSharp
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
Ajax.Utility.RegisterTypeForAjax(GetType(Ajax_CSharp))
End Sub
<Ajax.AjaxMethod(HttpSessionStateRequirement.ReadWrite)> _
Public Function GetData() As String
Try
Dim con As New SqlConnection(ConfigurationManager.AppSettings("conn"))
Dim cmd As New SqlCommand("SELECT * FROM employee", con)
cmd.Connection.Open()
Dim adapter As New SqlDataAdapter(cmd)
Dim ds As New DataSet("DataSet")
adapter.Fill(ds, "Table")
If ds.Tables(0).Rows.Count <= 0 Then
Return "Empty"
Else
Dim empID As String = ""
Dim empName As String = ""
Dim i As Integer
For i = 0 To ds.Tables(0).Rows.Count - 1
empID += ds.Tables(0).Rows(i)(0).ToString() + ","
empName += ds.Tables(0).Rows(i)(1).ToString() + ","
Next i
empID = empID.Substring(0, empID.Length - 1)
empName = empName.Substring(0, empName.Length - 1)
Return empID + "~" + empName
End If
Catch
Return "Error"
End Try
End Function |
|
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The key line is where the document is added to the current user's queue, which adds it to the session. Next, we'll create a user control, which can be placed on any page, used to notify the user when a queued document has become available. This user control will contain a single AJAX method, along with the code necessary to register the class with AJAX.
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