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[Bug] Can not use relative binding to assign view-to-view bindings #13664

Open Tommigun1980 opened 3 years ago

Tommigun1980 commented 3 years ago

Description

Assigning a view's binding context (for view-to-view bindings to work) can be accomplished as such:

<ContentView
    ....
    x:Name="viewRoot"
    BindingContext="{x:Reference viewRoot}" />

    <Label Text="{Binding SomeBinding}" />
</ContentView>

However, the exact same logic but using a relative binding instead of a named reference doesn't work:

<ContentView
    ....
    BindingContext="{RelativeSource Mode=Self}" />

    <Label Text="{Binding SomeBinding}" />
</ContentView>

Any bindings come out as blank, so for example the label's text will be blank.

Very much related issue: https://github.com/xamarin/Xamarin.Forms/issues/13669#issuecomment-773918838

Steps to Reproduce

See above.

Expected Behavior

View-to-view bindings should work even when a relative binding is used.

Actual Behavior

View-to-view bindings come out as blank when a relative binding is used to assign a view's binding context.

Tested this only on iOS.

Basic Information

Environment

Show/Hide Visual Studio info ``` === Visual Studio Community 2019 for Mac (Preview) === Version 8.9 Preview (8.9 build 1451) Installation UUID: dd55cb01-53ac-478e-8a82-b998d6898680 GTK+ 2.24.23 (Raleigh theme) Xamarin.Mac 6.18.0.23 (d16-6 / 088c73638) Package version: 612000113 === Mono Framework MDK === Runtime: Mono 6.12.0.113 (2020-02/4fdfb5b1fd5) (64-bit) Package version: 612000113 === Xamarin Designer === Version: 16.9.0.266 Hash: c4842c761 Branch: remotes/origin/c4842c761b9b6a95407f72278ca7fb42f8f7fdf0 Build date: 2021-01-07 06:17:08 UTC === Roslyn (Language Service) === 3.9.0-3.20619.14+df59a33fd9beff9790e01a2a1ab21e4a1e6921b3 === NuGet === Version: 5.8.0.6860 === .NET Core SDK === SDK: /usr/local/share/dotnet/sdk/5.0.102/Sdks SDK Versions: 5.0.102 5.0.101 5.0.100 3.1.405 3.1.404 3.1.403 MSBuild SDKs: /Applications/Visual Studio.app/Contents/Resources/lib/monodevelop/bin/MSBuild/Current/bin/Sdks === .NET Core Runtime === Runtime: /usr/local/share/dotnet/dotnet Runtime Versions: 5.0.2 5.0.1 5.0.0 3.1.11 3.1.10 3.1.9 === .NET Core 3.1 SDK === SDK: 3.1.405 === Xamarin.Profiler === Version: 1.6.15.68 Location: /Applications/Xamarin Profiler.app/Contents/MacOS/Xamarin Profiler === Updater === Version: 11 === Apple Developer Tools === Xcode 12.4 (17801) Build 12D4e === Xamarin.Mac === Xamarin.Mac not installed. Can't find /Library/Frameworks/Xamarin.Mac.framework/Versions/Current/Version. === Xamarin.iOS === Version: 14.9.0.27 (Visual Studio Community) Hash: f4c9327fa Branch: main Build date: 2020-11-19 10:57:31-0500 === Xamarin.Android === Version: 11.2.0.0 (Visual Studio Community) Commit: xamarin-android/d16-9/f908d16 Android SDK: /Users/tommikiviniemi/Library/Developer/Xamarin/android-sdk-macosx Supported Android versions: None installed SDK Tools Version: 26.1.1 SDK Platform Tools Version: 30.0.4 SDK Build Tools Version: 30.0.2 Build Information: Mono: 5e9cb6d Java.Interop: xamarin/java.interop/d16-9@1d382be ProGuard: Guardsquare/proguard/v7.0.1@912d149 SQLite: xamarin/sqlite/3.32.2@cfe06e0 Xamarin.Android Tools: xamarin/xamarin-android-tools/main@ad80a42 === Microsoft OpenJDK for Mobile === Java SDK: /Users/tommikiviniemi/Library/Developer/Xamarin/jdk/microsoft_dist_openjdk_1.8.0.25 1.8.0-25 Android Designer EPL code available here: https://github.com/xamarin/AndroidDesigner.EPL === Android SDK Manager === Version: 16.9.0.21 Hash: 57e40ba Branch: remotes/origin/main Build date: 2021-01-08 01:57:14 UTC === Android Device Manager === Version: 16.9.0.14 Hash: 0fdccda Branch: remotes/origin/main Build date: 2021-01-08 01:57:36 UTC === Build Information === Release ID: 809001451 Git revision: cfd15313a6388ef8dada0182e22a058131c46f9d Build date: 2021-01-15 08:42:21-05 Build branch: release-8.9 Xamarin extensions: cfd15313a6388ef8dada0182e22a058131c46f9d === Operating System === Mac OS X 10.16.0 Darwin 20.3.0 Darwin Kernel Version 20.3.0 Thu Jan 21 00:07:06 PST 2021 root:xnu-7195.81.3~1/RELEASE_X86_64 x86_64 ```

Workaround

Use a named reference to assign the binding context.

adammeaney commented 3 years ago

You need a Binding.

<ContentView
    ....
    BindingContext="{Binding Source={RelativeSource Mode=Self}}" />

    <Label Text="{Binding SomeBinding}" />
</ContentView>
jsuarezruiz commented 3 years ago

Seems to be the same (or very related) as https://github.com/xamarin/Xamarin.Forms/issues/13669