easyui 不识别json

<ul id="tt2"></ul>



$(function() {

    $('#tt2').tree({

        animate: true,

        url: 'data/test.ashx',

        onBeforeExpand: function(node, param) {

            $('#tt2').tree('options').url = "data/test.ashx";

        },               

        onClick:function(node){             

        alert(node.id); 

        } 



    })

后台代码

public void ProcessRequest(HttpContext context)

        {

            string str = "[{'id':1,'text':'Folder1','iconCls':'icon-ok','children':[{'id':2,'text':'File1','checked':true},{'id':3,'text':'Folder2','state':'open','children':[{'id':4,'text':'File2','attributes':{'p1':'value1','p2':'value2'},'checked':true,'iconCls':'icon-reload'},{'id':8,'text':'Folder3','state':'closed','children':[{'id':9,'text':'File31'},{'id':10,'text':'File32'}]}]}]},{'text':'Languages','state':'closed','children':[{'id':'j1','text':'Java'},{'id':'j2','text':'C#'}]}]";

            context.Response.ContentType = "text/plain";

            context.Response.Write(str);

            context.Response.End();

        }

但是页面无法显示，求助大神帮忙看一下
------解决方案--------------------
改成下面标准json格式试试，应该jq版本为1.4+怪异模式的json导致没执行success回调，参考：jQuery dataType指定为json的问题

//string str = "[{'id':1,'text':'Folder1','iconCls':'icon-ok','children':[{'id':2,'text':'File1','checked':true},{'id':3,'text':'Folder2','state':'open','children':[{'id':4,'text':'File2','attributes':{'p1':'value1','p2':'value2'},'checked':true,'iconCls':'icon-reload'},{'id':8,'text':'Folder3','state':'closed','children':[{'id':9,'text':'File31'},{'id':10,'text':'File32'}]}]}]},{'text':'Languages','state':'closed','children':[{'id':'j1','text':'Java'},{'id':'j2','text':'C#'}]}]";

//===>

string str ="[{\"id\":1,\"text\":\"Folder1\",\"iconCls\":\"icon-ok\",\"children\":[{\"id\":2,\"text\":\"File1\",\"checked\":true},{\"id\":3,\"text\":\"Folder2\",\"state\":\"open\",\"children\":[{\"id\":4,\"text\":\"File2\",\"attributes\":{\"p1\":\"value1\",\"p2\":\"value2\"},\"checked\":true,\"iconCls\":\"icon-reload\"},{\"id\":8,\"text\":\"Folder3\",\"state\":\"closed\",\"children\":[{\"id\":9,\"text\":\"File31\"},{\"id\":10,\"text\":\"File32\"}]}]}]},{\"text\":\"Languages\",\"state\":\"closed\",\"children\":[{\"id\":\"j1\",\"text\":\"Java\"},{\"id\":\"j2\",\"text\":\"C#\"}]}]";