Different behavior of DataTemplateSelector with enabled and disabled trim function

[M-Muluc]

Describe the bug

trim removes the code section used in WinUI to modify DataTemplate

protected override DataTemplate? SelectTemplateCore(object item, DependencyObject container)
{
    // some code
}

Steps to reproduce the bug

1. Enable trim and build project (in the attached repository trim is already enabled in the release and disabled in debug)

code

Expected behavior

Trim function does not delete used code sections.

Screenshots

Debug build:

2025-01-15.180449.mp4

Release build:

2025-01-15.180208.mp4

NuGet package version

None

Windows version

Windows 11 (24H2): Build 26100

Additional context

No response

[marcelwgn]

When trying to run your repro app in release, I get the following error:

1>C:\Program Files\dotnet\sdk\9.0.102\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Publish.targets(208,5): warning NETSDK1198: A publish profile with the name 'win-x64.pubxml' was not found in the project. Set the PublishProfile property to a valid file name.
1>C:\Users\User\.nuget\packages\microsoft.net.illink.tasks\8.0.12\build\Microsoft.NET.ILLink.targets(197,5): error NETSDK1102: Optimizing assemblies for size is not supported for the selected publish configuration. Please ensure that you are publishing a self-contained app.

Are there any steps I'm missing to run it in release?

[ghost1372]

@M-Muluc Disable Trim for Release Mode: (i tested on Release Mode and it is working fine @marcelwgn also Optimizing assemblie error will be fixed by disabling Trim)

<PublishTrimmed Condition="'$(Configuration)' != 'Debug'">False</PublishTrimmed>

or if you dont want to disable trim, you can add a publish profile.
add win-x64.pubxml under Properties\PublishProfile folder:

<?xml version="1.0" encoding="utf-8"?>
<!--
https://go.microsoft.com/fwlink/?LinkID=208121.
-->
<Project>
  <PropertyGroup>
    <Configuration>Release</Configuration>
    <Platform>x64</Platform>
    <PublishDir>bin\x64\Release\net8.0-windows10.0.19041.0\publish\</PublishDir>
    <PublishProtocol>FileSystem</PublishProtocol>
    <_TargetId>Folder</_TargetId>
    <TargetFramework>net8.0-windows10.0.19041.0</TargetFramework>
    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
    <SelfContained>false</SelfContained>
    <PublishSingleFile>false</PublishSingleFile>
    <PublishReadyToRun>false</PublishReadyToRun>
  </PropertyGroup>
</Project>

[M-Muluc]

@marcelwgn Sorry, gitignore deleted the files in question. I didn't modify them. I added them to the repository just in case.

Thanks @ghost1372 for the suggested solutions to the problem, it worked.

I'll leave the Issue open for now, as I believe trim should not remove these sections of code since they are used inside the WinUI. If I am wrong, you can close the Issue.

protected override DataTemplate? SelectTemplateCore(object item, DependencyObject container)
{
    return (item as ContentViewModel) switch
    {
        GreenContentViewModel => GreenTemplate,
        RedContentViewModel => RedTemplate,
        _ => new DataTemplate()
    };
}

[ghost1372]

@marcelwgn Sorry, gitignore deleted the files in question. I didn't modify them. I added them to the repository just in case.

Thanks @ghost1372 for the suggested solutions to the problem, it worked.

I'll leave the Issue open for now, as I believe trim should not remove these sections of code since they are used inside the WinUI. If I am wrong, you can close the Issue.

protected override DataTemplate? SelectTemplateCore(object item, DependencyObject container)
{
    return (item as ContentViewModel) switch
    {
        GreenContentViewModel => GreenTemplate,
        RedContentViewModel => RedTemplate,
        _ => new DataTemplate()
    };
}

enable trim again, and this time test with

<TrimMode>partial</TrimMode>
by default trimmode is full

[M-Muluc]

enable trim again, and this time test with

<TrimMode>partial</TrimMode> by default trimmode is full

Unfortunately this didn't work, the behavior remained the same

[lhak]

If you add <CsWinRTAotWarningLevel>2</CsWinRTAotWarningLevel> to the project file you will get some additional warnings. One of those is to mark the TemplateSelector class as partial. In my test, it will then work in release mode

[marcelwgn]

Closing this since it for NAOT trimming, some precautions need to be taken including making types partial. You can find more information on WinUI 3, C# and NAOT trimming here: https://github.com/microsoft/CsWinRT/blob/b1733e95c6d35b551fc8cf6fe04e2a0c287346dd/docs/aot-trimming.md