如何遍历块属性

Dim db As Database = Autodesk..ApplicationServices.Application.DocumentManager.MdiActiveDocument.Database
Dim ed As Editor = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument.Editor
Dim ent As PromptEntityResult = ed.GetEntity("请选择图框块")
        '判断是否选择成功
        If ent.Status = PromptStatus.OK Then
            Using transaction As Transaction = db.TransactionManager.StartTransaction()
                '获取选择的实体
                Dim entity1 As Entity
                entity1 = DirectCast(transaction.GetObject(ent.ObjectId, OpenMode.ForRead, True), Entity)