You will have to set the textbox's
AutoPostBack="true"
and also set the
OnTextChanged
of the textbox. The textbox's text changed event will fire only when you tab out of the control, it will not fire for each key press.
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Always">
<ContentTemplate>
<fieldset>
<asp:TextBox ID="TextBox1" runat="server" AutoPostBack="true" OnTextChanged="TextBox1_TextChanged"></asp:TextBox>
<br />
<br />
<asp:TextBox ID="TextBox2" runat="server" AutoPostBack="true" OnTextChanged="TextBox2_TextChanged"></asp:TextBox>
<br />
<br />
<asp:Label ID="Label1" runat="server"></asp:Label>
<br />
<br />
<asp:Label ID="Label2" runat="server"></asp:Label>
</fieldset>
</ContentTemplate>
</asp:UpdatePanel>
</div>
</form>
</body>
</html>