ClipboardRedux.RCW_IAgileReference.cs

using System;
using System.Runtime.InteropServices;

namespace WindowsFormsClipboardRedux
{
    partial class ClipboardRedux
    {
        internal class RCW_IAgileReference
        {
            private unsafe struct AgileReferenceVTable
            {
#pragma warning disable CS0649
                // Due to a bug in .NET Core 3.1 (3.1.18 as of now) we must inline IUnknown interface
                // members explicitly, and can't do the following:
                //
                //      public IUnknownVTable UnknownVTable;
                public delegate* unmanaged[Stdcall]<IntPtr, Guid*, IntPtr*, HRESULT> QueryInterface;
                public delegate* unmanaged[Stdcall]<IntPtr, HRESULT> AddRef;
                public delegate* unmanaged[Stdcall]<IntPtr, HRESULT> Release;

                // IAgileReference
                public delegate* unmanaged[Stdcall]<IntPtr, ref Guid, out IntPtr, HRESULT> Resolve;
#pragma warning restore CS0649
            }

            private readonly IntPtr _instance;
            private readonly unsafe AgileReferenceVTable* _vtable;

            public unsafe RCW_IAgileReference(IntPtr instance)
            {
                _instance = instance;
                _vtable = *(AgileReferenceVTable**)instance;
            }

            // An IAgileReference instance handles release on the correct context.
            ~RCW_IAgileReference()
            {
                if (_instance != IntPtr.Zero)
                {
                    Marshal.Release(_instance);
                }
            }

            public unsafe IntPtr Resolve(Guid iid)
            {
                // Marshal and dispatch
                _vtable->Resolve(_instance, ref iid, out IntPtr resolvedInstance)
                    .ThrowIfFailed();

                // Unmarshal
                return resolvedInstance;
            }
        }
    }
}