问如何使用C#添加保存文件对话框

EN

private void Save_As_Click(object sender, EventArgs e)
{
  SaveFileDialog _SD = new SaveFileDialog(); 
  _SD.Filter = "Text File (*.txt)|*.txt|Show All Files (*.*)|*.*";
  _SD.FileName = "Untitled"; 
  _SD.Title = "Save As";
  if (__SD.ShowDialog() == DialogResult.OK)
  {
   RTBox1.SaveFile(__SD.FileName, RichTextBoxStreamType.UnicodePlainText);
  }
}

var dialog = new Microsoft.Win32.SaveFileDialog();
dialog.Filter = "Rich Text File (*.rtf)|*.rtf|All Files (*.*)|*.*";
dialog.FileName = "Filename.rtf"; //set initial filename
if (dialog.ShowDialog() == true)
{
    using (var stream = dialog.OpenFile())
    {
       var range = new TextRange(myRichTextBox.Document.ContentStart,
                                 myRichTextBox.Document.ContentEnd);
       range.Save(stream, DataFormats.Rtf);
    }
}

var dialog = new Microsoft.Win32.SaveFileDialog();
dialog.Filter = "Text documents (.txt)|*.txt|All Files (*.*)|*.*"; 
dialog.FileName = "Filename.txt"; 
if (dialog.ShowDialog() == true)
{                
    File.WriteAllText(dialog.FileName, MyTextBox.Text);
}