public void OnConfirm(object sender, EventArgs e)
{
string confirmValue = Request.Form["confirm_value"];
if (confirmValue == "Yes")
{
//Your logic for OK button
ScriptManager.RegisterStartupScript(this, this.GetType(), "alert", "alert('you clicked yes'); OpenConfirmDialog();", true);
}
else
{
//Your logic for cancel button
ScriptManager.RegisterStartupScript(this, this.GetType(), "alert", "alert('you clicked no'); OpenConfirmDialog();", true);
}
}