'Interface not Registered' error on ATL ou

Question

I have an ATL in-process server that implements a callback interface like so:

.idl

interface IClientEvents : IUnknown{
    [] HRESULT TestEvent(void);
};

interface IATLSimpleObject : IDispatch{

    [id(1)] HRESULT Advise([in] IClientEvents* clientEvents);
    [id(2)] HRESULT Unadvise(void);
};

.h

private:
    IClientEvents* m_ClientEvents;
public:
    STDMETHOD(Advise)(IClientEvents* clientEvents);
    STDMETHOD(Unadvise)(void);

.cpp

STDMETHODIMP CATLSimpleObject::Advise(IClientEvents* clientEvents)
{
    m_ClientEvents = clientEvents;
    m_ClientEvents->AddRef();

    return S_OK;
}

STDMETHODIMP CATLSimpleObject::Unadvise(void)
{
    m_ClientEvents->Release();
    m_ClientEvents = NULL;

    return S_OK;
}

C# client

public partial class Form1 : Form, ATLProject1Lib.IClientEvents
{
    private ATLProject1Lib.ATLSimpleObject ATLSimple = new ATLProject1Lib.ATLSimpleObject();

    private void Form1_Shown(object sender, EventArgs e)
    {
        ATLSimple.Advise(this);
    }

    private void Form1_FormClosing(object sender, FormClosingEventArgs e)
    {
        ATLSimple.Unadvise();
    }

It works fine, but I need to do exactly the same in an out-of-process server, however, on execution I get an 'Interface not Registered' (80040105) error when calling 'ATLSimple.Advise(this)'.

I've spent hours searching for similar problems, but can't find anything. Any help would be greatly appreciated.

Answer 1

In order for this to work out-of-proc you need the interfaces to be marshalled between processes. Most likely you will want to rely on Automation marshalling which uses a typelib generated from your IDL to find what and how to marshall. The problem is that will only work for interfaces that are marked [oleautomation], [dual] or both in the IDL. See this answer for more details.

You best bet is marking the interfaces you want marshalled as [oleautomation] and adding a comment like "Marshalling magic goes away if you remove this".