将Addin对象转换为runtimeInterface Null或Exception

Question

当我尝试将COMAddIn强制转换回runtimeInterface时，我得到一个异常。 我尝试执行以下操作：

    foreach (COMAddIn addin in this.wordInstance.COMAddIns)
     {
        if (addin != null)
        {
           if (addin.Description == "Word2013AddIn")
           {
              this.runtimeInterface = (IRuntimeInterface)addin.Object;

           }
        }
     }

[ComVisible(true)]
[InterfaceType(ComInterfaceType.InterfaceIsDual)]
public interface IRuntimeInterface
{
   event EventHandler<EventArgs> Saving;
   void OnSaving(EventArgs e);
}

 [ComVisible(true)]
 [ClassInterface(ClassInterfaceType.None)]
 public class RuntimeInterface : StandardOleMarshalObject, IRuntimeInterface
 {
  public event EventHandler<EventArgs> Saving;
  public void OnSaving(EventArgs e)
  {
     EventHandler<EventArgs> handler = Saving;
     if (handler != null)
     {
        handler(this, e);
     }
  }
}

这是我得到的例外：

Unable to cast COM object of type 'System.__ComObject' to interface type 
'IRuntimeInterface'. This operation failed because the QueryInterface call on the COM
 component for the interface with IID '{E3FE02D2-EB95-383D-8301-3AF3260E92ED}' failed 
 due to the following error: No such interface supported (Exception from HRESULT:
 0x80004002 (E_NOINTERFACE)).