Validating multi-line text input when using .NET

Question

I have an HtmlTextArea and I want to restrict the number of characters users can input to 500.

Currently I've used a RegularExpressionValidator...

RegularExpressiondValidator val = new RegularExpressiondValidator ();
val.ValidationExpression = "^.{0,500}$";
val.ControlToValidate = id;
val.ErrorMessage = "blah";

... this is fine when the text is entered on a single line but it instantly fails validation whenever the text includes a new line character (ie. is multi-line).

I realise there are different regular expression engines and I need to test with the .NET one (can anyone point me in the direction of a good one online?) but I've tried a couple of other things including prepending "(?m)" to my expression string, and replacing ^ and $ with \A and \Z but so far no luck.

A further related question, can I avoid using a regular expression at all and link this validator to my own validation function somehow?

Answer 1

the "." does not include new lines.

^((.|\n){0,500})$

This page might also help, its a regex cheat sheet.

Answer 2

Change your regex to the following

"^(.|\n){0,500}$";

The . character matches everything except a newline. The or clause will fix your problem.

Answer 3

I would do this in two ways, if you know javascript and want to restrict the client side character length you could do it with jQuery (a popular javascript extension library).

$(document).ready(function(){
  var $TextBox = $("#<%=TextBox.ClientID %>");

  $TextBox.keyup(function(){
     return $TextBox.length <= <%=TextBox.MaxLength %>;
  });
});

Then do a similar check server-side with a Custom Validator or in your button click method.

There are also ways to enable and disable ASP.Net Validators with javascript so you could look into that as well.