private void btnNew_Click(object sender, EventArgs e)
        {
            switch (((Control)sender).Name)
            {
            case "btnNew":
                ITiers tier = new Tiers();
                id = tier.Nouveau();
                break;

            case "btnSave":
                Save_tier(true);
                break;

            case "btnDelete":
                Save_tier(false);
                break;
            }
        }