Proposal: Allow binding scopes in x:Bind

[weitzhandler]

Hi,

I used to set the DataContext to deeper scopes whenever necessary, so I can use shorter binding expressions: (ViewModel is of type ContactViewModel, that exposes a Phones collection property):

<Page DataContext="{Binding ViewModel}">
  <ListView ItemsSource="{Binding Phones}"/>
</Page>

I'm trying to use the above with x:Bind as follows, but seems that x:Bind would always bind against the page, not the current DataContext scope, which can lead to very verbose expressions.
My suggestion is that you allow scoping of x:Bind as well.

<Page DataContext="{x:Bind ViewModel}">
  <ListView ItemsSource="{x:Bind Phones}"/>
</Page>

But I get the following error:

XLS0432: The property 'Phones' was not found in type 'ContactsPage'. | MyProject.Client.UWP

Cross posted from here.

[stevenbrix]

This seems like it would require a fundamental difference in design for {x:Bind}.

How do you propose we enable this to happen?

[MikeHillberg]

Haven't thought about syntax, but it feels like some kind of a let clause scenario.

[stevenbrix]

As the user sees things, x:Bind doesn't use DataContext - that is what I was referring to about the fundamental difference in design.

Now we want to add a mode where it does bind to DataContext in some scenarios, but in others it uses the Page/UserControl.

I'm all for this, just not sure how to rationalize it in a way that doesn't cause things to blow up in complexity

[ranjeshj]

Propagating DataContext down the tree is quite expensive. If we can selectively propagate and scope down the tree explicitly using x:Bind, that would be great. In this specific scenario would x:Bind ViewModel.Phones work ?

[michael-hawker]

🦙 This is related to #2508 as well I think?