Returnering af en konpleks struktur fra en dll

Jeg fik hjælp til at kalde en c++ dll funktion med en struktur i dette spm: http://www.eksperten.dk/spm/842083.

Men jeg har også funktioner der returnere strukturer og for tiden har jeg klaret det ved:

namespace wpGrabDotNet.DllCode
{
  public class PointerToStruct<T> : IDisposable
    where T : struct
  {
    private T? outputStruct = null;

    public T? ToStruct
    {
      get
      {
        return outputStruct;
      }
    }

    public PointerToStruct(IntPtr ptr)
    {
      try
      {
        if (ptr != IntPtr.Zero)
        {
          //outputStruct = new T();
          outputStruct = (T) Marshal.PtrToStructure(ptr, typeof(T));
        }
      }
      catch(Exception ex)
      {
        outputStruct = null;
        throw new Exception(ex.Message);
      }
    }

    public void Dispose()
    {
      outputStruct = null;
    }
  }
}

Og strukturen der modtages er defineret ved (WPGRAB_STATUS_ENUM er en enumeration):

[StructLayout(LayoutKind.Sequential, CharSet=DLL_CHAR_SET)]
    public struct WPGrabUrlResourceStruct
    {
      public int id;
      public int masterId;
      public int errCode;
      //char* localFileName;
      public string url;
      public string errMsg;
      public WPGRAB_STATUS_ENUM status;
    };

    [StructLayout(LayoutKind.Sequential)]
    public struct WPGrabResourceFoundStructInt
    {
      public int masterId;
      public int webpageCount;
      public int imagesCount;
      public int otherCount;
      public IntPtr webpagePtr;
      public IntPtr imagePtr;
      public IntPtr otherPtr;
    };

    public struct WPGrabResourceFoundStruct
    {
      public int masterId;
      public WPGrabUrlResourceStruct? webpagesList;
      public WPGrabUrlResourceStruct? imagesList;
      public WPGrabUrlResourceStruct? otherList;
    };

Jeg kalder så dll funktionen med:

[DllImport(DLL_NAME, CallingConvention = DLL_CC, CharSet = DLL_CHAR_SET, EntryPoint = "WPGrabGetFoundResources")]
private static extern IntPtr WPGrabGetFoundResourcesInt(int index);

public static WPGrabResourceFoundStruct? WPGrabGetFoundResources(int index)
    {
      using (var output = new PointerToStruct<WPGrabResourceFoundStructInt>(WPGrabGetFoundResourcesInt(index)))
      {
        WPGrabResourceFoundStruct tmp = new WPGrabResourceFoundStruct();
        tmp.webpagesList = (WPGrabUrlResourceStruct?) (new PointerToStruct<WPGrabUrlResourceStruct>(output.ToStruct.Value.webpagePtr)).ToStruct;
        tmp.imagesList = (WPGrabUrlResourceStruct?)(new PointerToStruct<WPGrabUrlResourceStruct>(output.ToStruct.Value.imagePtr)).ToStruct;
        tmp.otherList = (WPGrabUrlResourceStruct?)(new PointerToStruct<WPGrabUrlResourceStruct>(output.ToStruct.Value.otherPtr)).ToStruct;

        return tmp;
      }
    }

Det virker meget besværligt... Er man virkelig nødt til selv at kopiere inner strukturer (f.eks. webpagesList) som kan være nullable??? Eller er der en bedre løsning???