void mbtnNewSoftwareUpgrade_Click(object sender, EventArgs e)
        {
            // Die Kundennummer ermitteln.
            var   title = "Kunden für neues Software-Upgrade suchen";
            Kunde kunde = null;
            var   csv   = new CustomerSearchView(title, false);

            csv.ShowDialog(this);
            if (csv.DialogResult == System.Windows.Forms.DialogResult.OK)
            {
                var customerRow = csv.SelectedCustomer;
                if (customerRow != null)
                {
                    kunde = Model.ModelManager.CustomerService.GetKunde(customerRow.Kundennummer, false);
                }

                // Die zu aktualisierende Kundensoftware ermitteln.
                Kundensoftware alteSoftware = null;
                var            ksv          = new KundensoftwareSearchView(kunde);
                ksv.ShowDialog(this);
                if (ksv.DialogResult == System.Windows.Forms.DialogResult.OK)
                {
                    alteSoftware = ksv.SelectedKundensoftware;
                }
                if (kunde != null && alteSoftware != null)
                {
                    var newUpgrade = Model.ModelManager.SoftwareService.AddSoftwareUpgrade(kunde, alteSoftware);
                    var suv        = new SoftwareUpgradeView(newUpgrade);
                    suv.Show();
                }
            }
        }
        void mlnkNeueVersion_Click(object sender, EventArgs e)
        {
            var ksv = new KundensoftwareSearchView(this.mySoftwareUpgrade.Kunde);

            ksv.ShowDialog(this);
            if (ksv.SelectedKundensoftware != null)
            {
                var versionId = ksv.SelectedKundensoftware.UID;
                var lizenz    = ksv.SelectedKundensoftware.Lizenzschluessel;
                this.mySoftwareUpgrade.NeueVersionId = versionId;
                this.mySoftwareUpgrade.NeueLizenz    = lizenz;
                this.mtxtNeueLizenz.Text             = lizenz;
            }
        }