如何在使用“保存文件”对话框保存文件时输入的无效文件名上显示消息框

嗨,我写了一个代码来显示一个消息框,如果在保存文件时输入了无效字符,但我的消息框没有显示。实际上,如果文件名开始或包含以下内容,我将有一个保存文件对话框选项来保存文件

             \\/:*?<>|"

我想在文件中将消息框显示为无效或非法字符

  Stream myStream;
    SaveFileDialog saveFileDialog1 = new SaveFileDialog();

   saveFileDialog1.InitialDirectory = @"C:\";
   saveFileDialog1.DefaultExt = "txt";
   saveFileDialog1.Filter = "(*.txt)|*.txt";
  saveFileDialog1.FilterIndex = 2;
  saveFileDialog1.RestoreDirectory = true;

 if (saveFileDialog1.ShowDialog() == DialogResult.OK)
 {
    FileName = saveFileDialog1.FileName;
    if ((FilePathHasInvalidChars(FileName)))
     {
         MessageBox.Show("File name should not contain \\/:*?<>|" ,"", MessageBoxButtons.OK, MessageBoxIcon.Error);
      }
     else
     {
         if ((myStream = saveFileDialog1.OpenFile()) != null)
         {

              //FileName = saveFileDialog1.FileName;
              if (!(FilePathHasInvalidChars(FileName)))
              {
                 TreeNode newNode = new TreeNode(FileName);
                 newNode.SelectedImageIndex = 1;
                 tvwACH.SelectedNode.Nodes.Add(newNode);
                 TreeNode NodeFileHeader = newNode.Nodes.Add("FileHeader");
                 myStream.Close();
               }

           }
        }

     }

    public static bool FilePathHasInvalidChars(string path)
    {

        return (!string.IsNullOrEmpty(path) && path.IndexOfAny(System.IO.Path.GetInvalidPathChars()) >= 0);
      }