Can't get iOS platform to build due to "error CS0006: Metadata file could not be found"

[VRage]

I try to compile a uno multi platform project for windows, wasm, android and ios. I've also referenced a multiplatform library which uses skiasharp. But the iOS platform gives me headache. I get 'CS0006: Metadata file 'D:\P\GdViewerControl.Views.Multi\obj\Debug\net8.0-ios\ref\GdViewerControl.Views.Multi.dll' could not be found' error while building.

Here is the binlog:
E3_CloudViewDemo_Multi_Debug_AnyCPU_Build_2024-09-02T07_04_02.8477278+02_00.binlog.zip

Csproj:

<Project Sdk="Uno.Sdk">
  <PropertyGroup>
    <TargetFrameworks>
      net8.0-android;
      net8.0-ios;
      net8.0-windows10.0.19041;
      net8.0-browserwasm;
    </TargetFrameworks>
      
    <OutputType>Exe</OutputType>
    <UnoSingleProject>true</UnoSingleProject>
      
    <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
        <!--<InvariantGlobalization>true</InvariantGlobalization>-->
    <!--<RuntimeIdentifiers Condition="$(TargetFramework.Contains('-android'))">android-arm;android-arm64;android-x86;android-x64</RuntimeIdentifiers>-->
    <!--<RuntimeIdentifier Condition="$(TargetFramework.Contains('-ios'))">ios-arm64</RuntimeIdentifier>-->

    <RootNamespace>Zuken.E3.Client.UI.Demo.$(MSBuildProjectName.Replace(" ", "_"))</RootNamespace>

      <!-- Display name -->
    <ApplicationTitle>E3_CloudViewDemo_Multi</ApplicationTitle>
    <!-- App Identifier -->
    <ApplicationId>Zuken.E3.Client.UI.Demo.E3_CloudViewDemo_Multi</ApplicationId>
    <!-- Versions -->
    <ApplicationDisplayVersion>1.0</ApplicationDisplayVersion>
    <ApplicationVersion>1</ApplicationVersion>
    <!--
      If you encounter this error message:

        error NETSDK1148: A referenced assembly was compiled using a newer version of Microsoft.Windows.SDK.NET.dll.
        Please update to a newer .NET SDK in order to reference this assembly.

      This means that the two packages below must be aligned with the "build" version number of
      the "Microsoft.Windows.SDK.BuildTools" package above, and the "revision" version number
      must be the highest found in https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref.
    -->
    <!-- <WindowsSdkPackageVersion>10.0.22621.28</WindowsSdkPackageVersion> -->

    <!--
      UnoFeatures let's you quickly add and manage implicit package references based on the features you want to use.
      https://aka.platform.uno/singleproject-features
    -->
    <UnoFeatures>
        Lottie;
        Storage;
        Hosting;
        Toolkit;
        Logging;
        Mvvm;
        Configuration;
        Navigation;
    </UnoFeatures>
      <UnoExtensionsVersion>4.1.24</UnoExtensionsVersion>
      <UnoToolkitVersion>6.0.24</UnoToolkitVersion>
      <UnoThemesVersion>5.0.13</UnoThemesVersion>
      <UnoCSharpMarkupVersion>5.2.14</UnoCSharpMarkupVersion>
  </PropertyGroup>
    <ItemGroup>
        <WasmShellExtraEmccFlags Include="-s INITIAL_MEMORY=64MB" />
        <WasmShellExtraEmccFlags Include="-s MAXIMUM_MEMORY=4GB" />
        <WasmShellExtraEmccFlags Include="-s ALLOW_MEMORY_GROWTH=1" />
        <WasmShellMonoEnvironment Include="MONO_GC_PARAMS" Value="soft-heap-limit=2048m,nursery-size=256m,evacuation-threshold=66,major=marksweep" />
    </ItemGroup>
    <PropertyGroup>
        <UnoSplashScreenFile>Assets\Splash\splash_screen.svg</UnoSplashScreenFile>
        <UnoSplashScreenBaseSize>600,600</UnoSplashScreenBaseSize>
    </PropertyGroup>
  <ItemGroup>
    <None Remove="Views\ProjectsPage.xaml" />
    <None Remove="Views\Shell.xaml" />
    <None Remove="Views\ViewerPage.xaml" />
  </ItemGroup>
  <ItemGroup>
    <ProjectReference Include="..\..\..\..\..\GdViewer\GdViewerControl.Views.Multi\GdViewerControl.Views.Multi.csproj" />
    <ProjectReference Include="..\..\Clients\ViewerModule.Client\ViewerModule.Client.csproj" />
  </ItemGroup>
    <ItemGroup>
      <UnoIcon Include="Assets\Icons\icon.svg" />
    </ItemGroup>
    <ItemGroup>
        <UnoImage Include="Assets\Icons\*" />
    </ItemGroup>
    <ItemGroup>
      <UnoImage Remove="Assets\Icons\icon.svg" />
      <UnoImage Remove="Assets\Icons\icon_foreground.svg" />
    </ItemGroup>
    <ItemGroup>
      <Reference Include="Flatbuffers">
        <HintPath>..\..\..\..\..\..\libs\flatbuffers\net\Flatbuffers\bin\Release\netstandard2.0\Flatbuffers.dll</HintPath>
      </Reference>
    </ItemGroup>
</Project>

[jeromelaban]

Thanks for the question. This generally means that the binary in question has not been built successfully. If you try building your app using the command line, you may get a different build error, or take a look at the very first build error from your build output in VS.

[VRage]

All projects and/or references were build without errors, also no projects were skipped. After digging depper the problem was, the references project were build into "net8.0-ios/win-x64" folder, instead of "net8.0/ios-arm64" or similar. I have no clue why. But that was the reason why the dll couldn't be copied to "net8.0-ios\ref".

[jeromelaban]

Thanks. In general, this happens if RuntimeIdentifiers is defined in a class library, when it should not. Did you define this property, and if so, why?

[VRage]

Yes, we have RuntimeIdentifiers defined:

<Project Sdk="Microsoft.NET.Sdk">
    <PropertyGroup>
        <TargetFrameworks Condition="$([MSBuild]::IsOSPlatform('windows')) or '$(EnableWindowsTargeting)' == 'true'">$(TargetFrameworks);net8.0-windows10.0.20348.0</TargetFrameworks>
        <TargetFrameworks>$(TargetFrameworks);net8.0;net8.0-ios;net8.0-android</TargetFrameworks>
        <!-- Ensures the .xr.xml files are generated in a proper layout folder -->
        <GenerateLibraryLayout>true</GenerateLibraryLayout>
        <RootNamespace>Zuken.E3.UI.GdViewerControl.Views.Multi</RootNamespace>
        <Platforms>AnyCPU</Platforms>
        <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
        <RuntimeIdentifiers Condition="$([MSBuild]::IsOSPlatform('windows')) or '$(EnableWindowsTargeting)' == 'true'">win-x64</RuntimeIdentifiers>
        <Configurations>Debug;Release</Configurations>
        <AppendRuntimeIdentifierToOutputPath>false</AppendRuntimeIdentifierToOutputPath>
    </PropertyGroup>
    <ItemGroup>
        <PackageReference Include="MathNet.Spatial" />
        <PackageReference Include="SkiaSharp" />
        <PackageReference Include="SkiaSharp.Views.Uno.WinUI" />
        <PackageReference Include="Uno.WinUI" />
    </ItemGroup>
    <Choose>
        <When Condition="$([MSBuild]::GetTargetPlatformIdentifier('$(TargetFramework)')) == 'windows'">
            <ItemGroup>
                <PackageReference Include="Microsoft.WindowsAppSDK" />
                <PackageReference Include="Microsoft.Windows.SDK.BuildTools" />
            </ItemGroup>
            <ItemGroup>
                <!--
				If you encounter this error message:

					error NETSDK1148: A referenced assembly was compiled using a newer version of Microsoft.Windows.SDK.NET.dll.
					Please update to a newer .NET SDK in order to reference this assembly.

				This means that the two packages below must be aligned with the "build" version number of
				the "Microsoft.Windows.SDK.BuildTools" package above, and the "revision" version number
				must be the highest found in https://www.nuget.org/packages/Microsoft.Windows.SDK.NET.Ref.
				-->
                <!-- <FrameworkReference Update="Microsoft.Windows.SDK.NET.Ref" RuntimeFrameworkVersion="10.0.22621.28" />
				<FrameworkReference Update="Microsoft.Windows.SDK.NET.Ref" TargetingPackVersion="10.0.22621.28" /> -->
            </ItemGroup>
        </When>
        <Otherwise>
            <ItemGroup>
                <Content Include="Assets\**" />
                <Page Include="**\*.xaml" Exclude="bin\**\*.xaml;obj\**\*.xaml" />
                <Compile Update="**\*.xaml.cs">
                    <DependentUpon>%(Filename)</DependentUpon>
                </Compile>
                <PriResource Include="**\*.resw" />
            </ItemGroup>
        </Otherwise>
    </Choose>
    <ItemGroup>
        <UpToDateCheckInput Include="**\*.xaml" Exclude="bin\**\*.xaml;obj\**\*.xaml" />
    </ItemGroup>
    <ItemGroup>
        <None Remove="Viewer.xaml" />
    </ItemGroup>
    <ItemGroup>
        <UpToDateCheckInput Remove="Viewer.xaml" />
    </ItemGroup>
    <ItemGroup>
        <ProjectReference Include="..\..\GdCommon\GdCommon.Types\GdCommon.Types.csproj" />
        <ProjectReference Include="..\GdViewerControl.Interfaces\GdViewerControl.Interfaces.csproj" />
        <ProjectReference Include="..\GdViewerControl.Rendering\GdViewerControl.Rendering.csproj" />
        <ProjectReference Include="..\GdViewerControl.ViewModels\GdViewerControl.ViewModels.csproj" />
    </ItemGroup>
    <ItemGroup Condition="'$(TargetFramework)' == 'net8.0-windows10.0.20348.0'">
        <PackageReference Include="SkiaSharp.Views.WinUI" />
        <PackageReference Remove="SkiaSharp.Views.Uno.WinUI" />
        <PackageReference Include="System.Drawing.Common" />
    </ItemGroup>
</Project>

Without defining it we get errors like error NETSDK1083: The specified RuntimeIdentifier 'win10-arm' is not recognized.

[jeromelaban]

Thanks. Then in this case, you may want to set the runtime identifiers only on the windows target frameworks. Note that this is a behavior that has been fixed when moving to uno.sdk class libraries.

[VRage]

Thank for the response, i guess the best way is to create a new cross platform library project, isn't it?