遍历一个实体对象，该实体对象是一个树形，并且获取所有的值类型，若是引用类型继续向下递归，如何实现？

遍历一个实体对象，该实体对象是一个树形，并且获取所有的值类型，若是引用类型继续向下递归，如何实现？
 internal void Test(Type type, string _xPath, XmlNamespaceManager _xmlNamespaceManager, XmlDocument _xmlDocument, object instance)
        {            System.Reflection.PropertyInfo[] _ropertyInfos = type.GetProperties();
            foreach (System.Reflection.PropertyInfo _propertyInfo in _ropertyInfos)
            {
                //Find all the attributes
                object[] _objects = _propertyInfo.GetCustomAttributes(false);
                //Assume the current property has not the XmlElementAttribute attribute.
                bool isHasNoXmlAttribute = false;
                foreach (object o in _objects)
                {
                    XmlAttributeAttribute _xmlAttributeAttribute = o as XmlAttributeAttribute;
                    if (_xmlAttributeAttribute != null)
                    {
                        isHasNoXmlAttribute = true;                        if (_propertyInfo.PropertyType == typeof(String))
                        {
                            string propertyValue = _propertyInfo.GetValue(关键是这里，无法获取孩子孙子对象的实体, null).ToString();
                           
                            XmlNode _xmlNode = _xmlDocument.DocumentElement.SelectSingleNode(_xPath, _xmlNamespaceManager);
                            //Assert.AreEqual(propertyValue, _xmlNode.Attributes[_xmlAttributeAttribute.a].Value);
                        }
                    }
                    XmlElementAttribute _xmlElementAttribute = o as XmlElementAttribute;
                    if (_xmlElementAttribute != null)
                    {
                        //the XmlElementAttribute attribute is existed.
                        isHasNoXmlAttribute = true;
                        string xmlns = this.GetXPath(_xmlElementAttribute.Namespace);
                        string typeName = _xmlElementAttribute.ElementName;
                        _xPath += "/" + xmlns + ":" + typeName;
                        instance = 这里很难实现.
                        this.Test(_propertyInfo.PropertyType, _xPath, _xmlNamespaceManager, _xmlDocument, instance);
                    }
                }
                //In the end, not find the XmlElementAttribute attribute.
                if (!isHasNoXmlAttribute)
                {
                    Assert.Fail("ASDFASDFASDFASDFASDFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF");
                }
            }
        }
谢谢!