ExtJs树展开报错

代码可能有点长，但是请大虾指教var TaskNode_MydhApplydo = new Ext.tree.TreeNode({
    text:'我的申请',
    expanded:false,
    leaf:false,
    id:'nod_myapplydo',
    qtip :'我的申请',
    iconCls:'add'
}); var TaskNode_MydhWaitdo = new Ext.tree.TreeNode({
    text:'我的待办',
    expanded:true,
    leaf:false,
    id:'nod_mywaitdo',
    qtip :'我的待办',
    iconCls:'add'
}); var TaskNode_MydhAllWaitdo = new Ext.tree.TreeNode({
    text:'全部流程',
    expanded:true,
    leaf:false,
    id:'nod_allWaitdo',
    qtip :'全部待办',
    iconCls:'add'
}); //树导航Panel
CTreePanel = function()
{
CTreePanel.superclass.constructor.call(this, {
id:'TreeNavPanel',
        region:'west',
        split:true,
        width: 180,
        minSize: 175,
        maxSize: 500,
        collapsible: true,
        margins:'0 0 5 5',
        cmargins:'0 0 0 0',
        rootVisible:true,
        lines:true,
        autoScroll:true,
        animCollapse:false,
        animate: false,
        collapseMode:'mini',
        collapseFirst:false,
root: new Ext.tree.TreeNode({
            text:'光路调度管理',
            id:'root',
            expanded:true         })
});
}
Ext.extend(CTreePanel, Ext.tree.TreePanel);
Ext.onReady(function(){    Ext.QuickTips.init();
pMain = new CMain();
    pTreePanel = new CTreePanel();
LoadDsTree();
pTreePanel.on('click', function(node, e) //树节点点击时 ，在TabPanel 中新增 tab 
{
if(node.attributes && node.attributes.href && node.attributes.href.length > 0)
{
e.stopEvent();
pMain.loadClass(node.attributes.href, node.id, node.text);
}
});

AddAllState();

var pViewPort = new Ext.Viewport({
        layout:'border',
        items:[pTreePanel, pMain]
    }); pViewPort.doLayout();
// AddHandler();
});function LoadDsTree()
{
    RemoveAllChildNode(pTreePanel.getRootNode()); //重新刷新树之前 将树节点清空一次
    pTreePanel.getRootNode().appendChild(DHManageNode); 
    pTreePanel.getRootNode().appendChild(DHApplyNode); 
    pTreePanel.getRootNode().appendChild(TaskNode_MydhApplydo);      
    pTreePanel.getRootNode().appendChild(TaskNode_MydhWaitdo);      
    pTreePanel.getRootNode().appendChild(TaskNode_MydhAllWaitdo);     
      
      LoadAllTree();        
}function LoadAllTree()
{
  LoadRsDsTree();
  LoadRAllDsTree();
   LoadRmyDsTree();
}//我的申请
function sendMyRequestLoadData(url,baseparams,pMyTreePanel)
{ 
   var NewAConnection = new Ext.data.Connection();   NewAConnection.request
   ({
        url: url,
        params: baseparams,     
        method: 'POST',
        callback: function(opts, success, response)  
        {
        if (success) 
        {                  
               
               var xrTable = new Ext.data.XmlReader({record: 'Table',id:''},[]);
               
               var rsTable = xrTable.read(response); 
               DealMyReaderString(rsTable,pMyTreePanel); 
        }    
        }
    });      
}//往节点里追加子节点
function DealMyReaderString(rsTable,pMyTreePanel)
{
    var tblNode = null ,rowText = null, rowUrl = null,rowId = null;    
    for(var i =0,len=rsTable.records.length;i<len;i++)  
    {
        tblNode = CreateMySubNode(rsTable.records[i],"my"+i);        pMyTreePanel.appendChild(tblNode); 
   }    pMyTreePanel.getRootNode().expand();
}//创建孙节点
function CreateMySubNode(record,i)
{
    var nodecount = record.node.attributes[0].value; //节点总数
    var tblUrl = record.node.attributes[1].value;    // url
    var tblText = record.node.attributes[2].value;  
    if(tblText!='已完成')
    {
      tblText = tblText.concat("("+nodecount+")");//节点文本
    }
    
    return CreateMyNode(tblText,i,tblUrl,false);
}/*
产生一个树节点
*/
function CreateMyNode(text,id,url,expanded)
{
    var nCreateNode = new Ext.tree.TreeNode({
                        text:text,
                        expanded:expanded,
                        id:id
                    });
    nCreateNode.attributes.href= url;
    
    return nCreateNode;            
}function LoadRsDsTree()
{    
    RemoveAllChildNode(TaskNode_MydhApplydo);  
   
    var RMyUrl = 'js/MyAddTree.asmx/GetMyAllNodes'
   sendMyRequestLoadData(RMyUrl,null,TaskNode_MydhApplydo);   
} setInterval(LoadRsDsTree, 60000);  // 1分钟读一次是数据库加载一次树节点function RemoveAllChildNode(parentNode)
{
    if(parentNode.childNodes.length == 0)
        return;
    
    while(parentNode.childNodes.length>0)
    {
        parentNode.removeChild(parentNode.childNodes[0]);
    }
}问题就是pMyTreePanel.getRootNode().expand();（//往节点里追加子节点
）这个方法里报我getRootNode()说不支持该属性或方法