xamarin/Xamarin.Forms

[Bug] Compiled bindings to work when also Binding the BindingContext in XAML

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#7,698 opened on Sep 26, 2019

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a/Xaml </>a/binding ⛓e/5 :clock5:help wantedt/bug :bug:up-for-grabs

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Description

Summary

Not sure if this a bug or a feature request.

When setting the BindingContext in XAML there is then no way to use compiled bindings.

For example

<custom:MyCustomView x:DataType="{x:Null}" BindingContext="{Binding PresenterViewModel}" IsVisible="{Binding IsVisible}" >
       <Label Text="{Binding Text}"/>
</custom:MyCustomView>

In the above code the datatype can only be Null

If you set it to any object, the two properties will conflict and say that either PresenterViewModel or IsVisible does not exist.

The bottom line is when ever you set BindingContext in Xaml, there is then no way to set DataType correctly

Contributor guide

Research direction
Investigate how compiled bindings resolve DataType when BindingContext is set in XAML; examine the binding infrastructure to understand the conflict and propose a fix.
Tech stack
csharp
Domain
mobile
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#XAMLXamarin.Forms
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45