为富文本框设置最大输入量，但允许其他特殊键

Question

我想检查并查看富文本框是否超过4000个字符，如果是，则不要添加到RTF。然而我遇到的问题是我似乎无法找到“允许特殊字符”的选项。我允许退格键和删除，但然后theres CTRL命令，移位等

private void RichEditControl_OnPreviewKeyDown(object sender, KeyEventArgs e) 
{ 
    var tr = new TextRange(richEditControl.Document.ContentStart, richEditControl.Document.ContentEnd); 

    e.Handled = (tr.Text.Length >= 4000 && !(e.Key == Key.Back || e.Key == Key.Delete)); 
} 

Answer 1

private void RichEditControl_OnPreviewKeyDown(object sender, KeyEventArgs e) 
{ 
    var tr = new TextRange(richEditControl.Document.ContentStart, richEditControl.Document.ContentEnd); 

    e.Handled = tr.Text.Length - richEditControl.Selection.Text.Length>= 4000; 
}