private void btnThem_Click(object sender, EventArgs e)
        {
            FrLstNhaXuatBanEdit frm = new FrLstNhaXuatBanEdit();

            frm.Tag = ""; //Tín hiệu cho biết thêm mới
            frm.ShowDialog();
            HienThiLstNhaXuatBan(Gr);
        }
        private void btnSua_Click(object sender, EventArgs e)
        {
            FrLstNhaXuatBanEdit fr = new FrLstNhaXuatBanEdit();

            fr                = new FrLstNhaXuatBanEdit();
            fr.Tag            = this.Gr.CurrentRow.Cells["Ma_NhaXuatBan"].Value.ToString(); //Tín hiệu sửa
            fr.txtMaNXB.Text  = this.Gr.CurrentRow.Cells["Ma_NhaXuatBan"].Value.ToString();
            fr.txtTenNXB.Text = this.Gr.CurrentRow.Cells["Ten_NhaXuatBan"].Value.ToString();
            fr.txtDiaChi.Text = this.Gr.CurrentRow.Cells["Dia_Chi"].Value.ToString();
            fr.ShowDialog();
            HienThiLstNhaXuatBan(Gr);
        }