let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: FileManager.SearchPathDomainMask.userDomainMask).first            let fileUrl = documentsUrl?.appendingPathComponent(response.suggestedFilename!)                        print(fileManager.fileExists(atPath: (fileUrl?.absoluteString)!))            //然而Swift检查不了视频是否存在.