来来来，都往这里看。以下代码不会再报错异常。

onSaveClick:function(){
    var that = this;
    wx.showLoading({
      title: '下载中...',
    })
    var filename = new Date().getTime()+".jpg";
    var savePath = wx.env.USER_DATA_PATH+"/"+filename
    wx.downloadFile({
      header:'content-type: image/jpg',
      url: that.data.img,
      filePath:savePath,
      success:function(res){
        wx.hideLoading({
          success: (res) => {},
        })
        var filePath = res.filePath
        that.setData({filePath:filePath})
        wx.getSetting({
          success: (res) => {
            console.log('getSetting', res);
            var writePhotosAlbum = res.authSetting['scope.writePhotosAlbum'];
            if (writePhotosAlbum == true) {
              that.saveImg()
            }else if(writePhotosAlbum==false){
              wx.showModal({
                title: '是否授权保存到相册',
                content: '需要获取您的保存图片权限，请确认授权，否则图片将无法保存到相册',
                success: function (tip) {
                  if (tip.confirm) {
                    wx.openSetting({
                      success: function (data) {
                        if (data.authSetting["scope.writePhotosAlbum"] === true) {
                          that.saveImg()
                        } else {
                          wx.showToast({
                            title: '授权失败',
                          })
                        }
                      }
                    })
                  }
                }
              })
            }else{
              that.saveImg()
            }
          },
          fail: function(res) {},
          complete: () => {}
        })
      }
    })
   
  },

  saveImg:function(){
    var filePath = this.data.filePath
    wx.showLoading({
      title: '保存中...',
    })
    wx.saveImageToPhotosAlbum({
      filePath: filePath,
      success: function (res) {
        wx.hideLoading({
          success: (res) => {},
        })
        wx.showToast({
          title: '保存成功',
          icon: 'success',
          duration: 1500,
        })
      },
      fail: function (res) {
        wx.showToast({
          title: "保存失败："+res.errMsg,
          icon: 'none',
          duration: 1500,
        })
      },
      complete: function (res) { },
    })
  },

这俩路径是一样的吧

save的时候应该用这个路径：