// 下载资源

    downLoad(){

    const downloadTask=  wx.downloadFile({

        url: 'https://image.baidu.com/search/detail?ct=503316480&z=0&ipn=d&word=%E5%9B%BE%E7%89%87&step_word=&hs=0&pn=6&spn=0&di=217690&pi=0&rn=1&tn=baiduimagedetail&is=0%2C0&istype=0&ie=utf-8&oe=utf-8&in=&cl=2&lm=-1&st=undefined&cs=2574107783%2C3717363313&os=1932447857%2C3979870278&simid=3353588432%2C341469820&adpicid=0&lpn=0&ln=1850&fr=&fmq=1627202924602_R&fm=&ic=undefined&s=undefined&hd=undefined&latest=undefined&copyright=undefined&se=&sme=&tab=0&width=undefined&height=undefined&face=undefined&ist=&jit=&cg=&oriquery=&objurl=https%3A%2F%2Fgimg2.baidu.com%2Fimage_search%2Fsrc%3Dhttp%3A%2F%2Fimg.pconline.com.cn%2Fimages%2Fupload%2Fupc%2Ftx%2Fphotoblog%2F1210%2F26%2Fc2%2F14676275_14676275_1351218242935_mthumb.jpg%26refer%3Dhttp%3A%2F%2Fimg.pconline.com.cn%26app%3D2002%26size%3Df9999%2C10000%26q%3Da80%26n%3D0%26g%3D0n%26fmt%3Djpeg%3Fsec%3D1629794924%26t%3D61ccaeb3f5c99ae4938a49e8722c2906&gsm=1e&rpstart=0&rpnum=0&islist=&querylist=&nojc=undefined',

        success(res){

          console.log(res);

        }

      });

      console.log(downloadTask);

      downloadTask.onProgressUpdate(result=>{

        console.log(result);

      })

    }

返回的result 里面的progress为null 为什么啊