[Desktop] x:Bind local does not work in Custom Control

[kucint]

Current behavior

Issue 1
binding to local constant works in Page but not working in Control

<Grid
  Width="{x:Bind local:MyControl.MyWidth}"
  Height="{x:Bind local:MyControl.MyHeight}" />

Code behind:

public sealed partial class MyControl : Control
{
    public const double MyWidth = 200;
    public const double MyHeight = 200;
}

Issue 2

Discrepancy between WinAppSDK and Desktop: WinAppSDK works fine with private const while Desktop requires public const

WinAppSDK

public sealed partial class MyControl : Control
{
    private const double MyWidth = 200;
    private const double MyHeight = 200;
}

Desktop

public sealed partial class MyControl : Control
{
    public const double MyWidth = 200;
    public const double MyHeight = 200;
}

Expected behavior

binding to local constant shall work in Control

How to reproduce it (as minimally and precisely as possible)

MINIMAL REPRO PROJECT: XBindLocalApp.zip

STEPS TO REPRODUCE:
run the app on Windows with WinAppSDK framework selected: all works fine:

run the app on Windows with Desktop framework selected: binding works in Page but fails in Control

Workaround

define constant in XAML rather than in C# code behind

Works on UWP/WinUI

Yes

Environment

No response

NuGet package version(s)

"Uno.Sdk": "5.4.8"

Affected platforms

Skia (WPF)

IDE

Visual Studio 2022

IDE version

No response

Relevant plugins

No response

Anything else we need to know?

No response

[kucint]

@MartinZikmund: still not working on "Uno.Sdk": "5.5.32"

[MartinZikmund]

@kucint This was more complex than I originally hoped. I think the PR I opened has the fix, but will need to validate it against all tests.

In the meantime a good way to workaround this could be to define the constants in XAML insted, e.g. in a resource dictionary you can do:

<x:Double x:Name="MyControlSize">200</x:Double>

And then use the resource in the template:

Width="{StaticResource MyControlSize}"

Ultimately the result should be equivalent, even performance-wise (and could actually even be more performant).

[kucint]

@MartinZikmund : defining constants in resources is XAML is not an option to me.
What could be an option to me is to add constant values to the resource dictionary from code behind.
Would it be as performant as adding them directly in XAML?

[MartinZikmund]

@kucint hopefully my PR will avoid the need for this, but yes, you could set the resources early on app startup from C#, it would have the same end result, while keeping the consts in C#

[kucint]

I upgraded my test app to the newest dotnet and newest "Uno.Sdk": "5.5.43": XBindLocalApp.zip
and it is still not working.

[kucint]

@MartinZikmund
Unfortunately, I ask you to reopen this issue, because the attached test app is still not working under newest dotnet and newest uno.sdk "Uno.Sdk": "5.5.43"

[jeromelaban]

The change is not present in uno 5.5, it will only be in Uno 5.6 at this time.

[kucint]

I see, is it present in dev branch?

[jeromelaban]

Not yet, we're currently ingesting the .NET 9 changes. It will be available in the dev branch most likely in the next few days.

[kucint]

Thanks @jeromelaban for info.