ExtJs Ext.tree.AsyncTreeNode 在loader的时候如何传参，使树刷新？？？

 //定义一个树  

　　var root=new Ext.tree.AsyncTreeNode({
            id:"-1",
            loader:new Ext.tree.TreeLoader({
                url:"GetData.aspx?temp="+temp,

　　　　　//此处temp的值想通过下面FormPanel的选择框传递过来
                listeners:{
                    "beforeload":function(treeloader,node)
                    {
                        treeloader.baseParams={
                        id:node.id,
                        method:'POST'
                        };
                    }
                }
            })
        });

//定义一个FormPanel

　var AddInfofp = new Ext.FormPanel(
    {
        region:'center',
        resizable:false,
        labelWidth:90,
        collapsible:true,
        closeAction:'hide',
        closable:true,
        plain : true,
        frame:true,
        border:false,
        layout: 'form',
        bodyStyle:"padding:5px 5px 5px 5px",
        items:[{
                    name:"dp_id",                           
                    xtype:"combo",
                    store:DataPrivstore,
                    mode:"remote",
                    displayField:"dp_name",
                    valueField:"dp_id",
                    forceSelection:true,
                    fieldLabel:"数据权限级",
                    editable:false,
                    typeAhead:true,
                    selectOnFocus:false,
                    triggerAction:"all",
                    allowBlank:false,
                    anchor:"90%",
                    listeners:{scope:this,
                               render : function(combo) {combo.setValue("门店");},
                               select:function()
                               {
                                    field=AddInfofp.form.findField("dp_id");
                                    if(field.isValid())
                                    {
                                        var valued=field.getValue();
                                        此处想根据COMBO下拉选择值来传递给上面的树，使树的数据重新加载

                                    }
                               }
                            }
                }]
      });

//后台GetData.aspx.cs
string temp = Request.Form["temp"];
此处获取前台temp值