请问微信小程序，将以下代码绑定到view组件上，点击上传图片后为什么报错

upLoadImage: function(event) {
       var id = event.currentTarget.id
       var that = this
       wx.chooseImage({
           count: 1, 
           sizeType: ['original', 'compressed'], 
           sourceType: ['album', 'camera'], 
           success: function(res) {
               var tempFilePaths = res.tempFilePaths
               wx.uploadFile({
                   url: '/wx/upload',
                   filePath: tempFilePaths[0],
                   name: 'image_file',
                   success: function (res) {

                   }
               })
           },
       })
    }

错误代码是：

uploadFile:fail Cannot read property '0' of null

感觉是tempFilePaths参数没有传入uploadFile函数中，但是函数中不是应该能读取外层函数的变量吗？