private void btnLapPhieuMoi_Click(object sender, EventArgs e)
{
i = 0;
Tien = 0;
txtTongtien.Text = "0";
btnGhiPhieu.Enabled = true;
btnLapPhieuMoi.Enabled = false;
btnThemSach.Enabled = false;
cboNXB.Enabled = true;
txtSoPN.Text = PhieuNhapBUS.GetIDPhieuNhap();
txtMaSach.ResetText();
txtTenSach.ResetText();
txtSoLuong.ResetText();
txtTacgia.ResetText();
txtGiaNhap.ResetText();
txtTheloai.ResetText();
dtkNgayNhap.Value = DateTime.Now;
dgvDanhSach.Rows.Clear();
}