ASP.NET RegularExpressionValidator, validate on a non-match?

Is there a way to use the RegularExpressionValidator to validate only when the ValidationExpression does not match? In particular use a PO BOX regex to validate an address that is NOT a PO BOX.

Thanks!

From stackoverflow

• Create a regular expression that validates NOT a PO BOX or use custom validator.

  ccook : I agree, this would be ideal. But inverting an existing regex is non trivial?

  Alex Reitbort : It depends on the regexp itself, but as far as I know there is no magic 'not' switch on the whole expression.

  ccook : Right, characters can be negated but not the whole expression (as far as i can tell). In the mean time it's a custom validator.

• Just use NegativeRegularExpressionValidator :)

  [ToolboxData("<{0}:NegativeRegularExpressionValidator runat=\"server\" ErrorMessage=\"NegativeRegularExpressionValidator\"></{0}:NegativeRegularExpressionValidator>")]
  public class NegativeRegularExpressionValidator : RegularExpressionValidator
  {
      protected override bool EvaluateIsValid()
      {
       return base.EvaluateIsValid() == false;
      }
  }
  

  ccook : Nice, I am going to give it a shot. ty

  Canavar : +1, but what about client side validation ?

  Mike Chaliy : Unfortunately, nothing about client side :(. Thank you for pointing this out. My aim was to give an idea, not more.

• Mike Chaliy's solution is very good, but it doesn't validate in client-side.

  I think you should use a custom validator control and write a javascript function that validates not a POBox. copy pattern from regular expression validator and use this site to write your own client side validation.

• You can effectively invert your regular expression using a negative look-ahead.

  For example, consider the following regular expression that matches only a string of digits:

  ^\d+$
  

  This expression could be inverted as follows:

  ^(?!\d+$).*$