谁能解决这个问题？谢谢了

//一级下拉框改变事件

public void field1_Changed(object sender, XmlEventArgs e)

        {

            XPathNavigator me = (XPathNavigator)sender;

            if (me.Value == "")

                return;

            // 主数据源

            XPathNavigator MainXpn = MainDataSource.CreateNavigator();

           //辅助数据源

            XPathNavigator RequestXpn = this.DataSources["getCodeTable"].CreateNavigator();

            RequestXpn.SelectSingleNode("/dfs:myFields/dfs:queryFields/tns:getCodeTable/tns:codeTabelSetType", NamespaceManager).SetValue("codetable.xml");

           

           

            //开始取参数

            RequestXpn.SelectSingleNode("/dfs:myFields/dfs:queryFields/tns:getCodeTable/tns:codeTabelType", NamespaceManager).SetValue(me.Value);

            //开始更新辅助数据源，问题出在这里：所有的二级下拉框菜单均访问这个数据源！

            //所以二级下拉框菜单将同时更新！

            this.DataSources["getCodeTable"].QueryConnection.Execute();

 

   //尝试遍历？

            XPathNodeIterator NodeIter = this.MainDataSource.CreateNavigator().Select("/my:myFields/my:group1/my:group2", this.NamespaceManager);

            string str1="";

            foreach (XPathNavigator item in NodeIter)

            {

                XPathNavigator n1 = item.SelectSingleNode("my:field1", NamespaceManager);

                str1 += n1.Value+",";

                //遍历毫无意义！因为所有的二级下拉框菜单还是访问最后一次遍历得到的数据源

    //只要下拉框使用数据源，下拉框的列表数据都将无法持久，选用其他方式的数据源还是会出现同样问题

                RequestXpn.SelectSingleNode("/dfs:myFields/dfs:queryFields/tns:getCodeTable/tns:codeTabelType", NamespaceManager).SetValue(n1.Value);

                this.DataSources["getCodeTable"].QueryConnection.Execute();

            }