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

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

            fr     = new FrLstLoaiSachEdit();
            fr.Tag = this.GrLoaiSach.CurrentRow.Cells["Ma_LoaiSach"].Value.ToString(); //Tín hiệu sửa
            fr.txtMaLoaiSach.Text    = this.GrLoaiSach.CurrentRow.Cells["Ma_LoaiSach"].Value.ToString();
            fr.txtTenMaLoaiSach.Text = this.GrLoaiSach.CurrentRow.Cells["Ten_LoaiSach"].Value.ToString();
            fr.ShowDialog();
            hienthi(GrLoaiSach);
        }