Validating Checkboxlist using CustomValidator

You might be knowing that required field validator doesn't works with required field validator... so to accomplish that purpose we can use custom validator to validate checkbox list.

<asp:CheckBoxList ID="chkModuleList"runat="server" >
</asp:CheckBoxList>

1) Using ClientValidationFunction

<asp:CustomValidator runat="server" ID="cvmodulelist" ClientValidationFunction="ValidateModuleList" ErrorMessage="Please Select Atleast one Module" ></asp:CustomValidator>

function ValidateModuleList(source, args)
{
var chkListModules= document.getElementById ('<%= chkModuleList.ClientID %>');
var chkListinputs = chkListModules.getElementsByTagName("input");
for(var i=0;i<chkListinputs .length;i++)
{
if(chkListinputs [i].checked)
{
args.IsValid = true;
return;
}
}
args.IsValid = false;
}

2) Using OnServerValidate

<asp:CustomValidator runat="server" ID="cvmodulelist" OnServerValidate="ValidateModuleList" ErrorMessage="Please Select Atleast one Module" ></asp:CustomValidator>

private void ValidateModuleList(object sender, ServerValidateEventArgs e)
{
int cnt= 0;

for(int i=0;i<chkModuleList.Items.Count;i++)
{
if(chkModuleList.Items[i].Selected)
{
cnt++;
}

e.IsValid = (cnt== 0) ? false : true;
}
}