sentence_widget.dart

class _SentenceWidgetState extends State<SentenceWidget> {
  bool isDisplayDefinition = false;
  Timer timer;

  @override
  Widget build(BuildContext context) {
    return ListTile(
      onTap: toggleDefinitionVisibility,
      contentPadding: EdgeInsets.all(8),
      title: Html(
        data: widget.sentence,
        defaultTextStyle: TextStyle(fontSize: 20),
      ),
      subtitle: Visibility(
        visible: isDisplayDefinition,
        child: Html(
          data: widget.explanation,
          defaultTextStyle: TextStyle(fontSize: 18),
        ),
      ),
    );
  }

  toggleDefinitionVisibility() {
    timer?.cancel();
    setState(() {
      isDisplayDefinition = !isDisplayDefinition;
    });

    if (isDisplayDefinition) {
      timer = Timer(Duration(seconds: 5), () => toggleDefinitionVisibility());
    }
  }

  @override
  void dispose() {
    timer?.cancel();
    super.dispose();
  }
}