How to highlight the line color while saving the data as stream in WPF EditControl?

_editor.PreviewKeyUp += OnPreviewKeyUp;
_editor.PreviewKeyDown += OnPreviewKeyDown;
 
private void OnPreviewKeyUp(object sender, KeyEventArgs e)
{
  switch (e.Key)
  {
    case Key.RightCtrl:
    case Key.LeftCtrl:
        _isCtrlDown = false;
        break;
    default: break;
  }
}
 
private void OnPreviewKeyDown(object sender, KeyEventArgs e)
{
  switch (e.Key)
  {
    case Key.RightCtrl:
    case Key.LeftCtrl:
        _isCtrlDown = true;
        break;
    case Key.S:
        if (_isCtrlDown)
        {
          SetFileText(_editor.Text);
          e.Handled = true;
        }
        break;
  }
}
 
private void SetFileText(string text)
{
  using (StreamWriter sw = new StreamWriter(_filePath))
  {
    sw.Write(text);
    MethodInfo methodInfo = this._editor.GetType().GetMethod("ChangeLinesState", BindingFlags.NonPublic | BindingFlags.Instance);
    methodInfo?.Invoke(this._editor, new object[] { LineModificationState.Modified, LineModificationState.Saved});
  }
}