title: Implement a RequiredIf and RequiredIfNot attribute validator, which depends on two values
body: <p>I need to implement a RequiredIF validator which depends on two values, a checkbox and a value selected from a dropdown.
  I need if possible something like</p>
  
  <pre><code>  [RequiredIf("Property1", true,"Property2,"value", ErrorMessageResourceName = "ReqField", ErrorMessageResourceType = typeof(RegisterUser))]
  </code></pre>