如何解析windows phone 8中的JSON文件

我在windows phone 8应用程序工作。我有一些JSON文件在我的项目。他们有html扩展。我想解析这些文件并获取内容，请帮忙。

[
{  "heading":"Employee details",
  "Sub":
    [
       {
            "Name":"james",
        "id":"ID1"
        },{
            "Name":"varun",
        "id":"ID2"
        },{
            "Name":"francis",
        "id":"ID4"
        }   
    ]
}
]

我已经尝试了以下代码

WebClient webClient = new WebClient();
                Uri uri = new Uri("http://Contents/details.html");
                webClient.OpenReadCompleted +=webClient_OpenReadCompleted;
                webClient.OpenReadAsync(uri);
void webClient_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
        {
            DataContractJsonSerializer ser = null;
            try
            {
                ser = new DataContractJsonSerializer(typeof(ObservableCollection<RootObject>));
                ObservableCollection<RootObject> details = ser.ReadObject(e.Result) as ObservableCollection<RootObject>;
                foreach (RootObject em in details)
                {
                    string name = em.Name;                    
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.InnerException.Message);
            }
        }  
    }