把一个base64 字符串解码后存为另外一个文件

void Main()  {      ConvertFromBase64String();  }    void ConvertFromBase64String()  {      string fileName = GetSaveFileName();      if ( fileName == null )      {          MessageBox.Show("No file name specified");      }      else      {          ConvertFromBase64String(fileName);      }  }    void ConvertFromBase64String(string saveFileName)  {      ConvertFromBase64String(Clipboard.GetText(), saveFileName);  }    void ConvertFromBase64String(string input, string saveFileName)  {      var contents = Convert.FromBase64String(input);        using (var fs = new FileStream(saveFileName, FileMode.Create, FileAccess.Write))      {          fs.Write(contents, 0, contents.Length);          fs.Flush();      }  }    string GetFileName(FileDialog fd)  {      bool? result = fd.ShowDialog();      if ( result != null && result.Value )      {          return fd.FileName;      }      return null;  }    string GetOpenFileName()  {      var ofd = new OpenFileDialog { Title = "Select text file", Filter = "All files (*.*)|*.*",          RestoreDirectory = true };      return GetFileName(ofd);  }    string GetSaveFileName()  {      var sfd = new SaveFileDialog { Title = "Save file as", Filter = "All files (*.*)|*.*",          RestoreDirectory = true };      return GetFileName(sfd);  }