protected void thanaDropDownList_SelectedIndexChanged(object sender, EventArgs e) { int id = Convert.ToInt32(thanaDropDownList.SelectedValue); centerDropDownList.DataSource = dropDownManager.GetAllCenter(id); centerDropDownList.DataTextField = "Name"; centerDropDownList.DataValueField = "Id"; centerDropDownList.DataBind(); ListItem liCenter = new ListItem("Select Center", "-1"); centerDropDownList.Items.Insert(0, liCenter); }