test:function(){
    wx.request({
      url: this.data.url,
      data:{
        id:6
      },
      header:{
        token:登录令牌,
      },
      method: ‘post‘,
      responseType: "arraybuffer", //此处是请求文件流，必须带入的属性
      success: function (res) {
          if(res.statusCode === 200){
              var imgSrc =  wx.arrayBufferToBase64(res.data);//二进制流转为base64编码
              var save = wx.getFileSystemManager();
              var number = Math.random();
              save.writeFile({
                  filePath: wx.env.USER_DATA_PATH + ‘/pic‘ + number + ‘.png‘,
                  data: imgSrc,
                  encoding: ‘base64‘,
                  success: res => {
                      wx.saveImageToPhotosAlbum({ //保存为png格式到相册
                          filePath: wx.env.USER_DATA_PATH + ‘/pic‘ + number + ‘.png‘,
                          success: function (res) {
                              wx.showToast({
                                  title: ‘下载成功‘,
                                  icon: ‘none‘,
                                  duration: 2000, //提示的延迟时间，单位毫秒，默认：1500
                              })
                          },
                          fail: function (err) {
                              console.log(err)
                          }
                      })
                  }, 
                  fail: err => {
                      console.log(err)
                  }
              })
          }
      },
      fail: function (error) {
          console.log(error);
      }
  });
  },