regular+required validation
<pre><code>&lt;asp:TextBox ID="Textboxtotalamount" OnTextChanged="AmountChanged"
         Width="90px" AutoPostBack="true" runat="server"&gt;
&lt;/asp:TextBox&gt;
&lt;asp:RequiredFieldValidator ID="RequiredFieldValidator" runat="server" 
         ControlToValidate="Textboxtotalamount"
         SetFocusOnError="True" ValidationGroup="val"&gt;*&lt;/asp:RequiredFieldValidator&gt;
&lt;asp:RegularExpressionValidator ID="RegularExpressionValidator1" runat="server"
         ControlToValidate="Textboxtotalamount"
         ValidationExpression="^[-+]?[1-9]\d{0,13}(\.\d{1,3})?%?$"
         SetFocusOnError="True"&gt;F&lt;/asp:RegularExpressionValidator&gt;
</code></pre>

<p>in this above code can validate correctly.......but in text box i  call "OnTextChanged"
event ....suppose if i type(characters)in textbox errormesge shown at the same time ontextchanged event also called hen error occured ....i ve to stop OnTextChanged event when regularexpression raised......
pls help</p>
