let downloadTask = wx.downloadFile({
      url: 'https://img.pic88.com/preview/2020/08/05/15966366371435355.jpg!s640',
      success: res => {
        if (res.statusCode == 200) {
          // 保存到相册
          wx.saveImageToPhotosAlbum({
            filePath: res.tempFilePath,
            success: res => {
              wx.showToast({
                title: '保存图片成功!~',
              });
            },
            fail: function (res) {
              wx.showToast({
                title: '保存图片失败!~',
                icon: 'none'
              });
            }
          })
        }
      }
    })
    //下载的进度
    downloadTask.onProgressUpdate((res) => {
      // console.log(res)
      if (res.progress === 100) {
        this.setData({
          progress: ''
        });
      } else {
        this.setData({
          progress: res.progress + '%'
        });
      }
    })