关于函数wx.getImageInfo的src未定义的问题

controlWH: function(obj) {

var that = this;

var tmpUrl = obj.url;

wx.getSystemInfo({

success: function(res) {

var screenW = res.screenWidth;

var screenH = res.screenHeight;

wx.getImageInfo({

src: that.data.tmpUrl,

success: function© {

that.setData({

screenW: res.screenWidth,

screenH: c.height / (c.width / res.screenWidth)

})

}

})

},

})

},

请大神指导，obj是一个数组，到wx.getImageInfo的src就报：

fail parameter error: parameter.src should be String instead of Undefined;

应该如何将tmpUrl赋值给src ？