点网核心 dll 为 COM dll 与事件

Question

Given it is possible to create a COM dll in Dot Net Core, in at least version 3.1 onwards...

Is it possible to create a COM dll that is capable of raising COM EVENTS that the client application (NOT dot net of any description) can hook up to?

I have succeeded in doing this with a dll built in Framework 3.5, but have had no success in the three times I've tried this in CORE.

Has anyone succeeded in doing this and have any tips or core they'd be kind enough to share.

Answer 1

Yes, it works as it should.

Here is a .NET Core 3.1 or .NET 5 COM class (follow more or less this tutorial and register: Exposing .NET Core components to COM ):

namespace ClassLibrary1
{
    [ComVisible(true)]
    [Guid("f39feec6-dd52-4da3-967a-c1e67de9346d")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    public interface IServer
    {
        void ComputePi();
        double GetComputedPi();
    }

    [ComVisible(true)]
    [Guid("5ff4acc2-2faa-4ea3-bae9-8c90fa67d75b")]
    [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)] // this is marked obsolete in .NET Core 3.1 but not any more in .NET 5
    public interface IServerEvents
    {
        [DispId(1234)]
        void OnPiComputed();
    }

    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    [ComSourceInterfaces(typeof(IServerEvents))] // this is marked obsolete in .NET Core 3.1 but not any more in .NET 5
    [Guid("32c58b14-b6fb-41f5-8368-52dc9289ae19")]
    public class Server : IServer
    {
        private event OnPiComputedEvent OnPiComputed;

        public delegate void OnPiComputedEvent();

        public void ComputePi()
        {
            Console.WriteLine("PI is being computed...");
            OnPiComputed?.Invoke();
        }

        public double GetComputedPi() => Math.PI;
    }
}

And for example, a .NET Framework COM client (interface are redefined exactly the same but you could create a common type library/.TLB or share a.cs):

class Program
{
    static void Main()
    {
        var type = Type.GetTypeFromCLSID(new Guid("32c58b14-b6fb-41f5-8368-52dc9289ae19"));
        var obj = (IServer)Activator.CreateInstance(type);

        var container = (IConnectionPointContainer)obj;
        var iid = typeof(IServerEvents).GUID;
        container.FindConnectionPoint(ref iid, out var point);
        
        var sink = new ServerEvents();
        point.Advise(sink, out var cookie);
        
        obj.ComputePi();
        Console.ReadKey(true);

        point.Unadvise(cookie);
    }
}

public class ServerEvents : IServerEvents
{
    public void OnPiComputed()
    {
        Console.WriteLine("PI was computed!");
    }
}

[ComVisible(true)]
[Guid("f39feec6-dd52-4da3-967a-c1e67de9346d")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface IServer
{
    void ComputePi();
    double GetComputedPi();
}

[ComVisible(true)]
[Guid("5ff4acc2-2faa-4ea3-bae9-8c90fa67d75b")]
[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
public interface IServerEvents
{
    [DispId(1234)]
    void OnPiComputed();
}

When ran, it should display:

PI is being computed...
PI was computed!