struct foo : public IDispatch
{
  // 通过 IDispatch 继承
  virtual ULONG AddRef(void) override{return 0;}
  virtual ULONG Release(void) override{return 0;}
    virtual HRESULT QueryInterface(REFIID riid, void ** ppvObject) override
     {
      if (riid == __uuidof(IUnknown))
      {
    *ppvObject = (IUnknown*)this;
    return S_OK;
      }
      IID uid;
      IIDFromString(L"{C#声明接口的GUID/IID}", &uid);
      if (riid == uid)
      {
         *ppvObject = (IDispatch*)this;// (IUnknown*)this;
         return S_OK;
       }
       if (riid == __uuidof(IDispatch))
       {
         *ppvObject = (IDispatch*)this;
         return S_OK;
       }
       return E_NOTIMPL;
　　　}
 
  virtual HRESULT GetTypeInfoCount(UINT * pctinfo) override{return S_OK;}
  virtual HRESULT GetTypeInfo(UINT iTInfo, LCID lcid, ITypeInfo ** ppTInfo) override{return S_OK;}
  virtual HRESULT GetIDsOfNames(REFIID riid, LPOLESTR * rgszNames, UINT cNames, LCID lcid, DISPID * rgDispId) override
  {
        *rgDispId = 1;
    return S_OK;
  }
 
  virtual HRESULT Invoke(DISPID dispIdMember, REFIID riid, LCID lcid, WORD wFlags, DISPPARAMS * pDispParams, VARIANT * pVarResult, EXCEPINFO * pExcepInfo, UINT * puArgErr) override
  {
        cout << "be called" << endl;
    return S_OK;
  }
};  

extern "C" __declspec(dllexport)
foo* WINAPI GetTestObject()
{
  return new foo;// 简单粗暴leak :)
}

[DllImport(@"foo.dll")]
static extern IntPtr GetTestObject();
 
 
[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
[Guid("your uiid")]
interface Test
{
  int func();
}
 
var v = GetTestObject();
obj = (Test)Marshal.GetObjectForIUnknown(v);
var value = obj.func();// 输出be called