代码片段： wx.downloadFile({       url: this.data.onUrl,       method:'GET',       success(res) {         console.log(res)         const fs = wx.getFileSystemManager();         fs.saveFile({           tempFilePath:res.tempFilePath, fileType: 'pdf',           filePath: wx.env.USER_DATA_PATH + '/' + Date.parse(new Date()) + '.pdf',           success:function(res){             console.log(res)             wx.openDocument({               filePath: res.savedFilePath,               showMenu: true,               success: function (res) {                 console.log('打开成功');               }             })           },           fail:function(res){             console.log(res)           }})       },       fail(res) {         console.log(res)       }     })