[C#] TEXT 로그남기기

/// ms까지 시간을 구하는 함수
public string GetDateTime()
{
    DateTime NowDate = DateTime.Now;
    return NowDate.ToString("yyyy-MM-dd HH:mm:ss") + ":" + NowDate.Millisecond.ToString("000");
}
 
 
/// 로그 기록
/// 로그내용
public void Log(string str)
{
    string FilePath = Application.StartupPath + @"\Logs\Log" + DateTime.Today.ToString("yyyyMMdd") + ".log";
    string DirPath = Application.StartupPath + @"\Logs";
    string temp;
 
    DirectoryInfo di = new DirectoryInfo(DirPath);
    FileInfo fi = new FileInfo(FilePath);
 
    try
    {
        if (di.Exists != true) Directory.CreateDirectory(DirPath);
 
        if (fi.Exists != true)
        {
            using (StreamWriter sw = new StreamWriter(FilePath))
            {
                temp = string.Format("[{0}] : {1}", GetDateTime(), str);
                sw.WriteLine(temp);
                sw.Close();
            }
        }
        else
        {
            using (StreamWriter sw = File.AppendText(FilePath))
            {
                temp = string.Format("[{0}] : {1}", GetDateTime(), str);
                sw.WriteLine(temp);
                sw.Close();
            }
        }
    }
    catch (Exception e)
    {
        MessageBox.Show(e.ToString());
    }
}