使用云开发上传多个图片，希望每个图片独立显示上传进度，但是进度永远只在图片数组最后一个的里面更新，这是为什么？

data: {
  // ...
  uploadImages: [],
}

user.chooseImage({
      count: count,
      sizeType: ['compressed'],
      sourceType: ['album', 'camera'],
    })
    .then(res=>{
      
      // 开始遍历
      for (var index in res.tempFilePaths) {
        var array = {
          'path': res.tempFilePaths[index],
          'progress': 0
        }
        that.data.uploadImages[index] = array

          const filePath = that.data.uploadImages[index].path
          const cloudPath = 'post-images_' + app.globalData.openid + '_' + common.getUniqueCode(new Date()) + '_' + index + filePath.match(/\.[^.]+?$/)[0]
          
          var uploadTask = wx.cloud.uploadFile({
            cloudPath,
            filePath,
            success: res => {
              console.log('上传成功', res.fileID)
            }
          })

          uploadTask.onProgressUpdate((res) => {
            // 把进度数据放入uploadImages数组
            that.data.uploadImages[index].progress = res.progress
            // 打印结果永远是最后一个数组对象更新progress，前几个progress一直都是0
            console.log('progress: ', that.data.uploadImages)

            that.setData({
              uploadImages: that.data.uploadImages
            })
         
          })
        }
     })