[求助]关于.net实现不了的功能，怎么办？

Public Class Class1
     Public Sub CreateBlockWithAttributes()
        Dim db As Database = HostApplicationServices.WorkingDatabase
        Dim blockId As ObjectId = ObjectId.Null
        Dim record As New BlockTableRecord
        record.Name = "RmNum"
        Using trans As Transaction = db.TransactionManager.StartTransaction
            Dim points As New Point3dCollection
            points.Add(New Point3d(-18, -6, 0))
            points.Add(New Point3d(18, -6, 0))
            points.Add(New Point3d(18, 6, 0))
            points.Add(New Point3d(-18, 6, 0))
            Dim pline As New Polyline2d(Poly2dType.SimplePoly, points, 0, True, 0, 0, Nothing)
            record.Origin = points(3)
            record.AppendEntity(pline)
            Dim attdef As New AttributeDefinition
            attdef.Position = New Point3d(100, 200, 0)
            attdef.Height = 8
            attdef.Rotation = 0
            attdef.HorizontalMode = TextHorizontalMode.TextMid
            attdef.VerticalMode = TextVerticalMode.TextVerticalMid
            attdef.Prompt = "Room Number;"
            attdef.TextString = "0000"
            attdef.Tag = "Number"
            attdef.Invisible = False
            attdef.Verifiable = False
            attdef.Preset = False
            attdef.Constant = False
            record.Origin = points(3)
            record.AppendEntity(attdef)
            Dim bt As BlockTable = trans.GetObject(db.BlockTableId, OpenMode.ForWrite)
            If bt.Has("RmNum") = False Then
                blockId = bt.Add(record)
                trans.AddNewlyCreatedDBObject(record, True)
                trans.Commit()
            End If
        End Using
    End Sub
End Class