UWP应用中如何将字符串写入日志文件

/// <summary>
        /// 写文本到系统缓存目录下 C:\Users\linzi\AppData\Local\Packages\316d8b79-0dd1-43cf-b834-09c991b404c6_fc3wzsjzxgev4\LocalState\OutputStreamLogs\
        /// </summary>
        /// <param name="PageOrClassName">错误来自哪个页面或者类</param>
        /// <param name="funName">方法名</param>
        /// <param name="text">日志信息</param>
        /// <param name="result">返回结果</param>
        public async static void WriteLog(string PageOrClassName, string funName, string text, string result)
        {
            try
            {
                StorageFolder rootFolder = null;

                var userFolder = await ApplicationData.Current.LocalFolder.TryGetItemAsync("OutputStreamLogs") as StorageFolder;
                string time = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss");
                if (userFolder == null)
                {
                    rootFolder = ApplicationData.Current.LocalFolder;
                    userFolder = await rootFolder.CreateFolderAsync("OutputStreamLogs");
                }
                string filename = DateTime.Now.ToString("yy-MM-dd") + ".log";
                var file = await userFolder.TryGetItemAsync(filename) as StorageFile;
                if (file == null)
                {
                    file = await userFolder.CreateFileAsync(filename, CreationCollisionOption.ReplaceExisting);
                    string str = "Exception:" + PageOrClassName + System.Environment.NewLine + "Time:" + time + System.Environment.NewLine + "Method:" + funName + System.Environment.NewLine + "Message:" + text + System.Environment.NewLine + "Result:" + result + System.Environment.NewLine + System.Environment.NewLine;
                    await Windows.Storage.FileIO.WriteTextAsync(file, str);
                }
                else
                {