private void LoadData()
        {
            var        data = context.layDanhSachUserLogin();
            DataTable  dt   = new DataTable();
            DataColumn dc0  = new DataColumn("Mã", typeof(string));
            DataColumn dc1  = new DataColumn("Tên đăng nhập", typeof(string));
            DataColumn dc2  = new DataColumn("Mật khẩu", typeof(string));
            DataColumn dc3  = new DataColumn("Quyền", typeof(string));
            DataColumn dc4  = new DataColumn("Mã nhân viên", typeof(string));
            DataColumn dc5  = new DataColumn("Tên nhân viên", typeof(string));

            dt.Columns.Add(dc0);
            dt.Columns.Add(dc1);
            dt.Columns.Add(dc2);
            dt.Columns.Add(dc3);
            dt.Columns.Add(dc4);
            dt.Columns.Add(dc5);

            foreach (var item in data)
            {
                DataRow row = dt.NewRow();
                row[0] = item.ma.ToString().Trim();
                row[1] = item.tendangnhap.ToString().Trim();
                row[2] = item.matkhau.ToString().Trim();
                row[3] = item.quyen.ToString().Trim();
                row[4] = item.manv.ToString().Trim();
                row[5] = item.ten.ToString().Trim();

                dt.Rows.Add(row);
            }
            gridControl.DataSource = dt;
            gridView1.Columns[0].AppearanceHeader.TextOptions.HAlignment = DevExpress.Utils.HorzAlignment.Center;
            gridView1.Columns[1].AppearanceHeader.TextOptions.HAlignment = DevExpress.Utils.HorzAlignment.Center;
            gridView1.Columns[2].AppearanceHeader.TextOptions.HAlignment = DevExpress.Utils.HorzAlignment.Center;
            gridView1.Columns[3].AppearanceHeader.TextOptions.HAlignment = DevExpress.Utils.HorzAlignment.Center;
            gridView1.Columns[4].AppearanceHeader.TextOptions.HAlignment = DevExpress.Utils.HorzAlignment.Center;
            gridView1.Columns[5].AppearanceHeader.TextOptions.HAlignment = DevExpress.Utils.HorzAlignment.Center;
        }