var comboxWithTree = new Ext.form.ComboBox({
                store : new Ext.data.SimpleStore({
                            fields : [],
                            data : [[]]
                        }),
                id : 'comboxWithTree',
                emptyText : '请输入拼音,如北京,输入bj,或从列表选择',
                width : 250,
                fieldLabel : "请选择",
                mode : 'local',
                triggerAction : 'all',
                selectedClass : '',
                enableKeyEvents : true,
                onSelect : Ext.emptyFn,
                listeners:{
                'keyup' : function(){
                    setNull();
                    searchText = comboxWithTree.getValue();
                }
            }
            });
    var root = new Ext.tree.AsyncTreeNode();
    var tree = new Ext.tree.TreePanel({
        height : 300,
        width : 250,
        autoScroll : true,
        animate : true,
        containerScroll : true,
        rootVisible : false,
        border : false,
        allowUnLeafClick : true,
        root : root,
        loader : new Ext.tree.TreeLoader({
                    dataUrl : 'xxxxxxxxxxxxxx',
                    baseParams : {
                        //此处不方便展示
                    }
                })
    });
    comboxWithTree.on('beforeRender', function() {
                comboxWithTree.tpl = "<div  id='" + randomid + "' ><div>";
            });
    comboxWithTree.on('expand', function() {
                tree.render("" + randomid + "");
            });