flutter_firestore_tut

.\lib\scr\home.dart

//...
class _Home extends State<StatefulWidget> {
  //...
  void switchListener(isOn) async {
    bool switcher;
    switch (isOn) {
      case true:
        switcher = true;
        _listener = Firestore.instance
            .collection('docs')
            .snapshots()
            .listen((data) => listenerUpdate(data));
        break;
      case false:
        switcher = false;
        await _listener.cancel();
        break;
    }
    setState(() {
      _switchOnOff = switcher;
    });
  }

  void listenerUpdate(data) {
    var number = data.documents.length;
    setState(() {
      _totalDocs = number;
    });
  }
  //...
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      //...
  }
}