private void txtTimKiem_KeyUp(object sender, KeyEventArgs e) { Class.XuLyThuVien KiemTra = new Class.XuLyThuVien(); if (txtTimKiem.Text == " " || txtTimKiem.Text == " ") { } else { GridViewTraCuuSach.DataSource = KiemTra.TraCuuSach(txtTimKiem.Text); if (GridViewTraCuuSach.DataSource == null || txtTimKiem.Text == null) { GridViewTraCuuSach.Rows.Clear(); GridViewTraCuuSach.Refresh(); } } }