c# 调用Delphi接口，接口返回的还是接口，而且返回的对象不在参数当中

Question

Delphi中方法定义
function CoDoorIntfFactory: IDoorIntfFactory; stdcall;

接口定义
IDoorIntfFactory = interface(IInterface)

['{F573C1C3-E0FD-44F4-8A32-4337B2FCF680}']

function CreateDDB(_host: wideString; _port: Integer): IDoorIntf; stdcall; end;

C#中实现
接口定义
[DllImport("DoorIntf.dll", EntryPoint = "CoDoorIntfFactory", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)]
//public static extern IDoorIntfFactory CoDoorIntfFactory();
public static extern void CoDoorIntfFactory([MarshalAs(UnmanagedType.Interface)] out IDoorIntfFactory instance);

方法调用
IDoorIntfFactory factory;

IAPApi.CoDoorIntfFactory(out factory);//调用成功，并返回IDoorIntfFactory
IDoorIntf xxx = factory.CreateDDB(dataIP, 0); //执行CreateDDB的时候无法执行。

报错了，调用不了，求大神助攻。

Answer 1

这是com dll，调用方法是
项目，添加引用，选择com引用，浏览，找到这个dll