Prevent closing of Ajax ModalPopupExtender on postback

This is the general problem face by developer even I also suffered from this problem. In my scenario, I was using RadioButtonList inside ModalPopupExtender. what i was facing when i changed the selection of RadioButton option, it was closing the Ajax ModalPopupExtender.

So what i did to prevent closing of ModalPopupExtender.

I put the modalpopupextender inside the UpdatePanel and in RadioButtonList1_SelectedIndexChanged event I called the  ModalPopupExtender show method. like that

 protected void RadioButtonListShippingMode_SelectedIndexChanged(object sender, EventArgs e)
{
        ModalPopupExtender1.Show();
}

It really solved my problem.