private void btnSua_Click(object sender, EventArgs e)
{
PHONG phong = PhongBLL.Get(x => x.Sophong == txtSP.Text);
phong.Sluongsv = Convert.ToInt32(cboSL.Text);
phong.LoaiPhong = cboLoaiPhong.Text;
PhongBLL.Edit(phong);
LoadPhong();
}