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);
        }