Check the Username for Availability Using ASP.Net AJAX



I designed a registration page in which a user enters user details like username, word etc. When the username is entered into the textbox I need to validate the username for availability. Availability depends on whether the username has been taken by another user; for that I am checking the username in the database. Here I have the problem that after the username is entered into the textbox I am getting the data from the database and showing the result on the page of whether that username is available or not but at that time the page gets a postback and loses the entered values from the textboxes; for that reason I used ajax to check username availability.

Now we can see how to check username availability in our application without postback; first add a reference for the AjaxControlToolkit to your application and also add:

<%@ Register Namespace="AjaxControlToolkit" Assembly="AjaxControlToolkit" tagPrefix="ajax" %>

To your aspx page and design your page likes this:

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Check Username availability Using Ajax</title>
<style type="text/css">
.waitingdiv {
background-color: #F5F8FA;
border: 1px solid #5A768E;
color: #333333;
font-size: 93%;
margin-bottom: 1em;
margin-top: 0.2em;
padding: 8px 12px;
width: 8.4em;
}
</style>
</
head>
<
body>
<
form id="form1" runat="server">
<asp:ScriptManager ID="scriptmanager1" runat="server">
</asp:ScriptManager>
<
script type="text/javascript">
Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(BeginRequestHandler);
function BeginRequestHandler(sender, args) {
var state = document.getElementById('loadingdiv').style.display;
if (state == 'block') {
document.getElementById('loadingdiv').style.display = 'none';
} else {
document.getElementById('loadingdiv').style.display = 'block';
}
args.get_postBackElement().disabled = true;
}
</script>
<
div>
<
asp:UpdatePanel ID="PnlUsrDetails" runat="server">
<ContentTemplate>
<
table>
<
tr>
<
td>
UserName:
</td>
<
td>
<
asp:TextBox ID="txtUsername" runat="server" AutoPostBack="true" ontextchanged="txtUsername_TextChanged"/>
</td>
<
td>
<
div id="checkusername" runat="server" Visible="false">
<asp:Image ID="imgstatus" runat="server" Width="17px" Height="17px"/>
<asp:Label ID="lblStatus" runat="server"></asp:Label>
</div>
</
td>
</
tr>
</
table>
<
div class="waitingdiv" id="loadingdiv" style="display:none; margin-left:5.3em">
<img src="LoadingImage.gif" alt="Loading" />Please wait...
</div>
</
ContentTemplate>
</
asp:UpdatePanel>
</
div>
</
form>
</
body>
</html>
If you observe in the above code I placed a textbox in an update panel to allow only partial postback; based on that we can avoid the complete postaback of the page when getting the data from the database and I set the property AutoPostBack="true" and used the ontextchanged="txtUsername_TextChanged" event to display the result after entering the text in the textbox.

Now add a
using System.Data.SqlClient; reference in the codebehind and use the attached code to get the username from the database.