下面附上核心代码

      let that = this

      wx.getSetting({

        success(res) {

          if (!res.authSetting['scope.writePhotosAlbum']) {

            wx.authorize({

              scope: 'scope.writePhotosAlbum',

              success(re) {

                that._saveToBlumNet(url)

              }

            })

          } else {

            that._saveToBlumNet(url)

          }

        }

      })

  _saveToBlumNet (url) {

    let that = this

    wx.downloadFile({

      url: url || that.shareobj.url,

      success: function (res) {

        wx.saveImageToPhotosAlbum({

          filePath: res.tempFilePath,

          success(result) {

            wx.showToast({

              title: '保存成功',

              icon: 'success',

              duration: 1000

            })

          },

          fail(result) {

            wx.showToast({

              title: '保存图片：' + result,

              icon: 'none',

              duration: 1000

            })

          }

        })

      },

      fail: function (res) {

        wx.showToast({

          title: '下载图片：' + res,

          icon: 'none',

          duration: 1000

        })

      }

    })

  }