Flutter: assertion: line 4269 pos 14 : 'owner!._debugCurrentBuildTarget == this': is not true - flutter

Question

I'm making an "inventory" app, to keep track of objects food etc in my house. I wanted to use a navigator, to make multiple pages, without "modifying" the widgets in the scaffold.
This is my code: (i have as you can see multiple file, ask me if you need something else)
Just to be clear, the utils.dart is an export file that I use to import every thing else
import 'package:flutter/material.dart';
import 'package:storage_system/utils.dart';
import 'package:flutter_barcode_scanner/flutter_barcode_scanner.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Storage System',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primarySwatch: Colors.yellow,
),
home: HomePage(),
);
}
}
class HomePage extends StatefulWidget {
const HomePage({Key? key}) : super(key: key);
#override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
int _index = 0;
void _onTap(int i) {
setState(() {
_index = i;
});
}
Future<void> getBarcodeData() async {
String resultData = await FlutterBarcodeScanner.scanBarcode(
"0xFFFFFF", "Close", false, ScanMode.BARCODE);
print(resultData);
}
Widget selectPage(int i) {
switch (i) {
case 0:
return MainPage();
case 1:
return SettingsPage();
default:
return Container();
}
}
#override
Widget build(BuildContext context) => Navigator(
onGenerateRoute: (settings) => MaterialPageRoute(
builder: (context) => Container(
child: Scaffold(
floatingActionButtonLocation:
FloatingActionButtonLocation.centerDocked,
floatingActionButton: FloatingActionButton(
onPressed: getBarcodeData,
child: Icon(Icons.add),
),
appBar: AppBar(
actions: <Widget>[],
title: Text(
"Storage System",
textAlign: TextAlign.center,
style: TextStyle(fontSize: 28),
),
),
bottomNavigationBar: BottomNavigationBar(
items: <BottomNavigationBarItem>[
BottomNavigationBarItem(
icon: Icon(Icons.home), label: "Home"),
BottomNavigationBarItem(
icon: Icon(Icons.settings), label: "Setings")
],
currentIndex: _index,
onTap: _onTap,
elevation: 15,
),
body: Container(
child: selectPage(_index),
),
),
)),
);
}