How can I try out the NativeAOT compatible interfaces with CsWinRT 3.0?

[Jan Martin (catmanjan)]

e.g. I have a csproj:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net10.0-windows10.0.26100.1</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
	  <CsWinRTIncludes>Windows.Storage.Provider</CsWinRTIncludes>
	  <PublishAot>true</PublishAot>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Windows.CsWinRT" Version="3.0.0-preview.260319.2" />
    <PackageReference Include="Microsoft.Windows.SDK.Contracts" Version="10.0.26100.1" />
  </ItemGroup>

</Project>

When I have a look at the type definitions coming from cswinrt they're missing the ComGeneratedInterface attribute - is there perhaps another flag I need to set?

[Dongle (dongle-the-gadget)]

CsWinRT 3.0 doesn't use GeneratedComInterface, as it does not use .NET's source generated COM Wrappers. It uses its own COM Wrappers implementation.

[Jan Martin (catmanjan)]

Does that mean I won’t be able to use it to implement interfaces for COM with NativeAOT?

…

On Fri, 17 Apr 2026 at 5:45 pm, Minh Dang Binh ***@***.***> wrote: CsWinRT 3.0 doesn't use GeneratedComInterface, as it does not use .NET's source generated COM Wrappers. It uses its own COM Wrappers implementation. — Reply to this email directly, view it on GitHub <#2394 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AABBRBS3OP3HRTLCEZ5R2PT4WHOKNAVCNFSM6AAAAACX4RLIL6VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTMNRQGAYDGOI> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[Jan Martin (catmanjan)]

My bad, see attached ComIssue.zip

I changed my ClassFactory to implement a custom IClassFactory definition rather than the CsWin32 one - I noticed there is a test in this repo that does the same (https://github.com/search?q=repo%3Amicrosoft%2FCsWinRT%20iclassfactory&type=code) and I now get an accessviolationexception, unsure if that is progress in the right direction... haha...

[Jan Martin (catmanjan)]

Dongle (@dongle-the-gadget) sorry I don't want to mess up that PR anymore than I already have - here is a sample of what I am trying to do, as far as I can tell I've done everything right to get NativeAOT COM interop working but I either get no interface, or an accessviolationexception

Can you have a look at ComIssue.zip for me? e.g. do I need to implement the ABI.* methods?

[Dongle (dongle-the-gadget)]

Jan Martin (@catmanjan) so there are two issues you need to solve:

• Access violation: Replace the ref Guid riid in IClassFactory with in Guid riid. riid here is an immutable field so in needs to be used instead of ref.
• Missing interface: This is caused by the CsWinRT CCW generator being disabled by default on libraries. There are two ways to solve this:
  • Add [GeneratedWinRTExposedType] to your StorageProviderStatusUIFactory class.
  • Set <CsWinRTAotOptimizerEnabled>Auto</CsWinRTAotOptimizerEnabled> in your ShellService project.

[Jan Martin (catmanjan)]

Dongle (@dongle-the-gadget) thanks for that! That did it...

One more question - CsWin32 generates an IClassFactory with a CreateInstance definition of public unsafe void CreateInstance([MarshalAs(UnmanagedType.Interface), Optional] object pUnkOuter, Guid* riid, [MarshalAs(UnmanagedType.Interface)] out object ppvObject)

Unlike the custom IClassFactory which passes out an IntPtr...

Is there any way to use the cswin32 classfactory with cswinrt? setting object ppvObject to the iinspectable pointer doesn't work, no does "re-marshalling" using As<>

e.g.

    [GeneratedComClass]
    [Guid("7E9C7DDD-CB25-4D98-AECB-5BCD3D66C935")]
    public partial class ClassFactory : Windows.Win32.System.Com.IClassFactory
    {
        public unsafe void CreateInstance([MarshalAs(UnmanagedType.Interface), Optional] object pUnkOuter, Guid* riid, [MarshalAs(UnmanagedType.Interface)] out object ppvObject)
        {
            var instance = new StorageProviderStatusUIFactory();

            // none of these work
            ppvObject = instance;
            ppvObject = MarshalInspectable<IStorageProviderStatusUISourceFactory>.FromManaged(instance);
            ppvObject = MarshalInspectable<IStorageProviderStatusUISourceFactory>.FromManaged(instance).As<IStorageProviderStatusUISourceFactory>();
        }

        public void LockServer(BOOL fLock)
        {
        }
    }
    ```

[Dongle (dongle-the-gadget)]

Unfortunately there's no way, since CsWin32 in this case uses .NET StrategyBasedComWrappers which is incompatible with CsWinRT's its own `ComWrappers'.