public BillingEntryDetailPage()
        {
            InitializeComponent();

            var item = new BillingEntry()
            {
                Id = Guid.NewGuid()
            };

            viewModel      = new BillingEntryDetailViewModel(item);
            BindingContext = viewModel;
        }
        public BillingEntryDetailPage(BillingEntryDetailViewModel viewModel)
        {
            InitializeComponent();

            BindingContext = this.viewModel = viewModel;
        }