title: asp:RequiredFieldValidator validation based on conditions
body: <p>I have validation as below but only like to triggered if the checkbox is ticked.</p>
  
  <pre class="lang-asp prettyprint-override"><code>&lt;!-- TextBox and its validator --&gt;
  Name: &lt;asp:TextBox ID="TextBox1" runat="server" /&gt;
  
  &lt;asp:RequiredFieldValidator runat="server"
          ID="RequiredFieldValidator1" 
          Text="*"
          ErrorMessage="Name is required" 
          ControlToValidate="TextBox1" /&gt;
  </code></pre>
  
  <p>Can I get it done using asp:RequiredFieldValidator?<br>
  I only like to validate if a certain condition matched.<br>
  Currently it is validating every time the 'Save' button is clicked.</p>