Invalid cast from 'WinRT.IInspectable' to 'IMemoryBufferByteAccess' (`GeneratedComInterface`)

[lostmsu]

It's basically this issue, but it only happens when I replace [ComImport] with [GeneratedComInterface].

Describe the bug
Given

[GeneratedComInterface]
[Guid("5B0D3235-4DBA-4D44-865E-8F1D0E4FD04D")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public unsafe partial interface IMemoryBufferByteAccess
{
    void GetBuffer(out IntPtr buffer, out uint capacity);
}

Attempting to convert IMemoryBufferReference reference to IMemoryBufferByteAccess fails with

System.InvalidCastException: 'Invalid cast from 'WinRT.IInspectable' to 'ChatGPT.Platforms.Windows.Core.IMemoryBufferByteAccess'.'

To Reproduce
See the linked issue

1. IMemoryBufferReference reference = ...
2. reference.As<IMemoryBufferByteAccess>()

Expected behavior
Should get IMemoryBufferByteAccess

Version Info
.NET SDK 8.0 - net8.0-windows10.0.22621.0

Additional context

[dongle-the-gadget]

GeneratedComInterface isn’t allowed right now as the NuGet version does not contain the .NET 8 WinRT.Runtime that contains this functionality.

[Sergio0694]

Yeah this is caused by the fact we're not shipping the .NET 8 TFM yet, so this is expected. That said, it definitely shouldn't be needed to manually define IMemoryBufferByteAccess, do interop with that interface and use that directly just to get data out of an IMemoryBufferReference instance. I've opened #1673 to add a helper API to do this much more easily (and efficiently) 🙂