Change textbox's css class when ASP.NET Validation fails

Question

How can I execute some javascript when a Required Field Validator attached to a textbox fails client-side validation? What I am trying to do is change the css class of the

Answer 1

Alternatively, just iterate through the page controls as follows: (needs a using System.Collections.Generic reference)

const string CSSCLASS = " error";    

protected static Control FindControlIterative(Control root, string id)
{
   Control ctl = root;
   LinkedList ctls = new LinkedList();
   while ( ctl != null )
   {
     if ( ctl.ID == id ) return ctl;
     foreach ( Control child in ctl.Controls )
     {
       if ( child.ID == id ) return child;
       if ( child.HasControls() ) ctls.AddLast(child);
     }
     ctl = ctls.First.Value;
     ctls.Remove(ctl);
   }
   return null;
}



protected void Page_PreRender(object sender, EventArgs e)
{
  //Add css classes to invalid items
  if ( Page.IsPostBack && !Page.IsValid )
  {
    foreach ( BaseValidator item in Page.Validators )
    {
       var ctrltoVal = (WebControl)FindControlIterative(Page.Form, item.ControlToValidate);
       if ( !item.IsValid ) ctrltoVal.CssClass += " N";
       else ctrltoVal.CssClass.Replace(" N", "");
    }
  }
}

Should work for most cases, and means you dont have to update it when you add validators. Ive added this code into a cstom Pageclass so it runs site wide on any page I have added validators to.