在代码隐藏中访问XAML绑定

Question

I am working in Xamarin but I believe this applies to any UWP application using XAML.

First I have two ContentPages. On the first page, I want to pass some data to the second page, so I do this as part of the navigation:

    async void BuyTickets(object sender, EventArgs e)
    {
        var ticketOrderTotal = new TicketOrder
        {
            OrderTotal = lblOrderAmount.Text,
            OrderTotalList = ticketsPrices.Where(o => o.TicketQuantity > 0).ToList<Ticket>()
        };

        var paymentPage = new PaymentPage();

        paymentPage.BindingContext = ticketOrderTotal;

        await Navigation.PushAsync(paymentPage);
    }

The above works fine in XAML. On the second page (PaymentPage), I am able to reference the BindingContext like this, for example, and the Text property is correct:

<Label x:Name="lblOrderAmount" Text="{Binding OrderTotal}" />

What I would like to do is access the "{Binding OrderTotal}" value in the C# code-behind of the second page. I found a way to do this, too, but it just does not seem optimal. This is the kludge I have in place:

<Label x:Name="lblOrderAmount" Text="{Binding OrderTotal}" BindingContextChanged="GetChargeAmount" />

And this is the code-behind for the label:

    public static string m_charge_amount = "";
    ...
    private void GetChargeAmount(object sender, EventArgs e)
    {
        var lbl = ((Label)sender);
        m_charge_amount = lbl.Text;
    }

So my question is this: is there a better way to do this? It is particularly hard to research as XAML seems to be rooted in WPF, Silverlight, Xamarin, Windows 8, and now Windows 10 (UWP). It is all over the place. I am constantly fighting with the framework to do things that I think should be quite easy to do....like this. Please help but do be nice .

Thank you.

EDIT:

Per @Jason's comment, you can pass an object to the page constructor, and that will work. This is what the re-worked function looks like now:

    async void BuyTickets(object sender, EventArgs e)
    {
        var ticketOrderTotal = new TicketOrder
        {
            OrderTotal = lblOrderAmount.Text,
            OrderTotalList = ticketsPrices.Where(o => o.TicketQuantity > 0).ToList<Ticket>()
        };

        var paymentPage = new PaymentPage(ticketOrderTotal);

        paymentPage.BindingContext = ticketOrderTotal;

        await Navigation.PushAsync(paymentPage);
    }

And then the result from debugging:

Answer 1

instead of having PageA set PageB's BindingContext , instead pass the ticketOrderTotal object as a parameter on PageB's constructor. Then PageB can set it's own BindingContext as well as keep a local reference to the ticketOrderTotal object.