how to change the defult boolen value in flutter

Question

I'm using bool value as default as false and after my, onpress event, it's changed but refreshes the screen it comes back to default value again how to fix this.

 class _MarketState extends State<Market> {
  final _database = FirebaseDatabase.instance.ref().child('data/market/');
  bool _sortvalue = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Scrollbar(
        child: StreamBuilder(
        stream: _database.onValue,
        builder: (context, snapshot) {
          final valudisp = <Card>[];
          if (snapshot.hasData) {
            final firstdata = (snapshot.data! as DatabaseEvent)
                .snapshot
                .value as Map<Object?, dynamic>;
            final data = firstdata.values.toList();
            if (_sortvalue == false) {
              data.sort((a, b) => a['Quantity'].compareTo(b['Quantity']));
            } else {
              data.sort((a, b) => a['tradep'].compareTo(b['tradep']));
            }

            final sdata = List.from(data.reversed);
            Set<Object> dataset = Set.from(sdata);
            dataset.forEach((element) {
              final datalast = element as Map<dynamic, dynamic>;
              final coinname = datalast['namedata'];
              final diff = datalast['dif'];
              final time = datalast['Time'];
              final Quantity = datalast['Quantity'];
              final tradep = datalast['tradep'];
              Color signalcolor =
                  diff > 0 ? Color(0xff008b45) : Color(0xffB3000C);
              final displaycard = Card(...);
      floatingActionButton: FloatingActionButton(
        child: Icon(
            _sortvalue ? Icons.bar_chart_rounded : Icons.attach_money_rounded),
        onPressed: () {
          setState(() => _sortvalue = !_sortvalue);
        },

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