Change Text Box Color using Required Field Validator. No Extender Controls Please

Question

I need to change color of TextBox whenever its required field validator is fired on Clicking the Submit button

Answer 1

I too liked Alexanders and Steves answer but I wanted the same as in codebehind. I think this code might do it but it differes depending on your setup. My controls are inside a contentplaceholder.

protected void cvPhone_ServerValidate(object source, ServerValidateEventArgs args)
{
    bool is_valid = !string.IsNullOrEmpty(args.Value);
    string control = ((CustomValidator)source).ControlToValidate;
    ((TextBox)this.Master.FindControl("ContentBody").FindControl(control)).CssClass = is_valid ? string.Empty : "inputError";
    args.IsValid = is_valid;
}