private void DgvDonhang_CellContentClick(object sender, DataGridViewCellEventArgs e)
 {
     txtMadh.Text      = dgvDonhang.CurrentRow.Cells[0].Value.ToString();
     txtTenKH.Text     = db.getTenKH(Convert.ToInt32(dgvDonhang.CurrentRow.Cells[1].Value.ToString()));
     txtPhi.Text       = dgvDonhang.CurrentRow.Cells[2].Value.ToString();
     txtNgaydat.Text   = dgvDonhang.CurrentRow.Cells[4].Value.ToString();
     cbbTinhtrang.Text = dgvDonhang.CurrentRow.Cells[3].Value.ToString();
 }