Future _scanQR() async {
    List<Barcode> barcodes = [];
    try {
    barcodes = await FlutterMobileVision.scan(
        flash: false,
        autoFocus: true,
        formats: Barcode.ALL_FORMATS,
        multiple: false,
        showText: true,
        camera: FlutterMobileVision.CAMERA_BACK,
        fps: 30.0,
    );
    setState(() {
        result = barcodes[0].displayValue;
    });
    } on Exception {
    barcodes.add(new Barcode('Failed to get barcode.'));
    }
}

@override
Widget build(BuildContext context) {
    ...
    body: Center(
    ...
    floatingActionButton: FloatingActionButton.extended(
        icon: Icon(Icons.camera_alt),
        label: Text("Scan"),
        onPressed: _scanQR,
    ),
    floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
    );
}

class History extends StatefulWidget {
  @override
  HistoryState createState() {
    return HistoryState();
  }
}

class HistoryState extends State<History> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Scanner History"),
        ),
        body: new ListView.builder(
            itemCount: 1,
            itemBuilder: (context, index) {
              return ListTile(title: Text("ニート"));
            }));
  }
}

class HistoryState extends State<History> {
  List<ScanItem> _items = [];

  @override
  void initState() {
    super.initState();
    _initDatabase();
  }

  _initDatabase() async {
    String path = await getDatabaseFilePath("scan_history.db");
    Database db = await openReadOnlyDatabase(path);

    List<Map> data = await db.query("scan_hisoty", columns: ["text"]);

    List<ScanItem> items = [];
    data.forEach((e) => items.add(ScanItem.fromMap(e)));

    setState(() {
      _items = items;
    });

    await db.close();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        ...
        body: new ListView.builder(
            itemCount: _items.length,
            itemBuilder: (context, index) {
              return ListTile(title: Text("${_items[index].text}"));
            }));
  }
}