Xamarin.forms: Support binding to attached BP

[StephaneDelcroix]

The current Binding system doesn't allow to use an attached bindable property as binding source, like in

<Grid>
    <Label x:Name="label0" Grid.Row="1"/>
    <Label Text="{Binding (Grid.Row), Source={x:Reference label0}}" />
</Grid>

Of course, it can be combined as part of a complex path

<Label Text="{Binding label0.(Grid.Row)}" />

If the attached BP owner type is not in the default xmlns, the type has to be prefixed

<Label Text="{Binding label0.(local:MyLayout.Altitude)}" />

For this reason, this syntax is restricted to xaml only.

Challenges:

• attach changed handlers to attached BPs
• keep the current bindings working while refactoring

Formal syntax for Binding Path

_part-element-list_:

• _empty_
• _part-separator_
• _first-part_ _part-list_(opt)

_empty_:

_part-separator_:

• .

_first-part_:

• _part_
• _part-separator_ _part_

_part-list_:

• _part-separator_ _part_
• _part-separator_ _part_ _part-list_(opt)

_part_:

• _part-id_
• _indexer_

_part-id_:

• identifier
• (_type_._bp_)

_type_:

• identifier
• xmlnsprefix:identifier

_indexer_:

• _part_id_[index]

[AtosNicoS]

This issue is listed for the x:Bind project:
https://github.com/xamarin/Xamarin.Forms/projects/7

What is the current status of the x:bind implementation?

[ddobrev]

When is this planned for fixing?

[groege]

Bump

[YZahringer]

Any news on that?

[tuyen-vuduc]

I am also looking for this feature to work as well.

[JunkyXL86]

Same here

[mattleibow]

Nooo! I _just_ needed to use this in my templated view!

[YZahringer]

Could be 5.0.0 candidate?