Ajax in UserControl

i have a signup page and i want to check username exists or not with ajax

 <%@ Control Language="C#" AutoEventWireup="true" CodeFile="Simple.ascx.cs" Inherits="UserControls_Simple" %>
<div style="direction:rtl;">
<table style="font-family:Tahoma;font-size:12px;width:200px;">
<tr>
<td>نام کاربری:</td>
<td><asp:TextBox ID="txtUserName" runat="server"></asp:TextBox></td>
</tr>
<tr>
<td>
    <asp:Label ID="lblMessage" runat=开发者_如何学JAVA"server" Text="Username Already Exists" Visible="False"></asp:Label>
</td>
<td>
</td>
</tr>
<tr>
<td>کلمه عبور</td>
<td><asp:TextBox ID="txtPassword" runat="server"></asp:TextBox></td>
</tr>
</table>
</div>

i want to show label if user exists

how can i do that?

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Using Ajax to check if a user exists in your DB via a User Control (or whatever method you are using) is the same method you would use in a Web Page.

What kind of Ajax do you want to use? MS Ajax, jQuery, what?

Regardless, you will need to Call Web Services from Client Script to perform an AJAX request.