You can validate this in client side like this
if i click on that checkbox i want that corrsponding ID that' why am saving that id in hidden field. if you did't select any check box the checkedIDs length will be zero
$('[id^="MainContent_rptrFollowup_chkSelect_"]').live("click", CheckCheckBox);
var checkedIDs = "";
function CheckCheckBox() {
var tempid = $(this)[0].id.split('_')[parseInt($(this)[0].id.split('_').length) - 1];
if ($(this).is(":checked")) {
if (checkedIDs.search($("#MainContent_rptrFollowup_hdnchkPatientAppointmentID_" + tempid).val()) < 0) {
checkedIDs += $("#MainContent_rptrFollowup_hdnchkPatientAppointmentID_" + tempid).val() + ":";
}
}
else {
if (checkedIDs.search($("#MainContent_rptrFollowup_hdnchkPatientAppointmentID_" + tempid).val()) >= 0) {
checkedIDs = checkedIDs.replace($("#MainContent_rptrFollowup_hdnchkPatientAppointmentID_" + tempid).val() + ":", '');
}
}
}
function chekCkeckBox() {
var isChecked = false;
if (checkedIDs.length > 0) {
$('#MainContent_hdnChkSendMail').val(checkedIDs);
isChecked = true;
}
if (isChecked)
return true;
else {
AlertDialog('You are required to select at least one item from the list to send email.', "eMeditime - Send Mail");
return false;
}
return true;
}