Server Side Validation of CheckboxList in ASP.NET & C#

We can Validate CheckboxList using the CustomValidator on Client side and server-side as well.

Our approach here will be validating the checkboxlist on server-side.

1. Add the CheckboxList with some items as below.

<asp:CheckBoxList ID="CheckBoxList1" runat="server">
          <asp:ListItem>A</asp:ListItem>
          <asp:ListItem>B</asp:ListItem>
          <asp:ListItem>C</asp:ListItem>
 </asp:CheckBoxList>

2. Add a CustomValidator Control from the toolbox.

I have added a OnServerValidate event which will validate the checkboxlist on server side on button click.


            <asp:CustomValidator ID="CustomValidator1" runat="server" ErrorMessage="Please select alteast one option"  OnServerValidate="CustomValidator1_ServerValidate" ></asp:CustomValidator>

3. Add a Button to Check the Validations are working.

 <asp:Button ID="Button1" runat="server" Text="Button" />

4. the c# code for validating the list.

 protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args)
        {
            int count = 0;
            foreach (ListItem item in CheckBoxList1.Items)
            {
                if (item.Selected)
                {
                    count++;
                    break;
                }
            }

            if (count > 0)
                args.IsValid = true;
            else
                args.IsValid = false;

        }