private void btnAdd_Click(object sender, EventArgs e)
        {
            FrmEdit      form = new FrmEdit(0, this.customers);
            DialogResult res  = form.ShowDialog();

            if (res == DialogResult.OK)
            {
                this.UpdateView();
                this.WriteCustomerDB();
            }
        }
        private void btnBalance_Click(object sender, EventArgs e)
        {
            if (this.lbxCustomer.SelectedIndices.Count > 1)
            {
                this.lbxCustomer.SelectedIndex = this.lbxCustomer.SelectedIndices[0];
            }
            FrmEdit      editForm = new FrmEdit(2, this.customers, lbxCustomer.SelectedIndex);
            DialogResult res      = editForm.ShowDialog();

            if (res == DialogResult.OK)
            {
                this.WriteCustomerDB();
                this.UpdateView();
            }
        }