Use 4Guys Creating CheckBox and CheckBoxList Validators in ASP.NET 2.0, you can build a custom validator control for your Checkbox and checkboxlist. But if you have more than one CheckBoxList in your page, the validator will not work because the Javascript will only apply to one control.

What you can do is modify the validator class to create an individual javascript for each validator.

In GenerateClientValidation method

change to:


Attributes["evaluationfunction"] = "VerifyItemSelected_" + <strong>ControlToValidate</strong>;

StringBuilder scriptBuilder = new StringBuilder();

scriptBuilder.Append(@"&lt;script language='javascript'&gt;");
scriptBuilder.Append(string.Format("function VerifyItemSelected_{0}", <strong>ControlToValidate</strong>));
scriptBuilder.Append(@"() {");
scriptBuilder.Append(string.Format("var targetControlName = document.getElementById('{0}')", this.ClientID));



Page.ClientScript.RegisterClientScriptBlock(typeof(CheckBoxListValidator), “CustomCheckboxListValidationScript_” + ControlToValidate, scriptBuilder.ToString());

By changing the code, we can ensure all the validator scripts are being registered.