protected void districtDropDownList_SelectedIndexChanged(object sender, EventArgs e) { int id = Convert.ToInt32(districtDropDownList.SelectedValue); thanaDropDownList.DataSource = dropDownManager.GetAllThana(id); thanaDropDownList.DataTextField = "Name"; thanaDropDownList.DataValueField = "Id"; thanaDropDownList.DataBind(); ListItem liThana = new ListItem("Select Thana", "-1"); thanaDropDownList.Items.Insert(0, liThana); }