爲富文本框設置最大輸入量，但允許其他特殊鍵

Question

我想檢查並查看富文本框是否超過4000個字符，如果是，則不要添加到RTF。然而我遇到的問題是我似乎無法找到「允許特殊字符」的選項。我允許退格鍵和刪除，但然後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; 
}