无法解析json数据

Question

尝试解析从Web服务返回的以下有效json数据;

{"SwipeArray":[
    {"UserID": "@xxxxxxxx",
     "Date": "8/24/2011 10:41:38 AM",
     "Lab": "5"
    }
]}

使用此代码;

      $.ajax({
             type: "POST",
             ... etc
             contentType: "application/json; charset=utf-8",
             dataType: "json",
             success: function (json1) {
var y = json1.SwipeArray[0].Lab;

在上面的第一行获取此错误;

Microsoft JScript runtime error: 'SwipeArray.0' is null or not an object