protected void thanaDropDownList_SelectedIndexChanged(object sender, EventArgs e) { int id = Convert.ToInt32(thanaDropDownList.SelectedValue); List <Center> aCenterList = aCenterManager.GetAllCenterByThanaId(id); centerDropDownList.DataSource = aCenterList; centerDropDownList.DataTextField = "Name"; centerDropDownList.DataValueField = "Id"; centerDropDownList.DataBind(); }