title: Stop postback on TextChanged
body: <p>I have a textbox in an aspx page that has a TextChanged event attached to it.
  I also have a validator attached to the textbox.</p>
  
  <p>When the text is changed, the validate triggers but in case there is an error the textchanged event is still called. Do you know if it's possible to stop the postback on textchanged if the validator fires?</p>
  
  <pre><code>&lt;asp:TextBox ID="txtQuantity" runat="server" AutoPostBack="true" ontextchanged="txtQuantity_TextChanged"&gt;&lt;/asp:TextBox&gt;
  &lt;asp:RequiredFieldValidator ID="reqQuantity" ControlToValidate="txtQuantity" runat="server" ErrorMessage="The quantity is mandatory."&gt;&lt;/asp:RequiredFieldValidator&gt;
  </code></pre>