private bool KiemTraTraCuuSach() { var slSachSeMuon = dgvSachMuon.Rows.Count - 1; var slSachToiDa = DocGia_BUS.LaySachMuonToiDa(txtMaDocGia.Text.ToInt32()); if (slSachToiDa == null) { return(false); } if (slSachSeMuon == slSachToiDa) { return(false); } return(true); }