ASP.NET CheckboxList Validation with RequiredFieldValidator

In order to use a RequiredFieldValidator with a CheckBoxList, you need to define your own CheckBoxList class that inherits from CheckBoxList , but also implements a ValidationPropertyAttribute  method:

    [ValidationPropertyAttribute("ValidateableProperty")]
    public class ValidateableCheckBoxList : CheckBoxList
    {
 
        public string ValidateableProperty
        {
            get
            {
                string result = "";
                int count = 0;
                foreach (ListItem item in this.Items)
                {
                    if (item.Selected)
                    {
                        count++;
                    }
 
                }
                if (count > 0)
                {
                    result = count.ToString();
                }
                else
                {
                    result = "";
                }
                return result;
            }
        }
    }

You can then create a ValidateableCheckBoxList and point a required validator's controlToValidate attribute to it.

SOURCE:
http://pedroliska.wordpress.com/2009/08/13/getting-an-asp-net-checkboxlist-to-work-with-a-requiredfieldvalidator/