Flutter passed arguments return null allways

Question

In this simple flutter GitHub repository implementation we have a simple screen which we want to pass arguments and getting them in destination screen, for example

form ScreenA() we want pass arguments to ScreenB()

defined routes:

routes: {
  '/page/one': (context) => ScreenA(),
  '/page/two': (context) => ScreenB(),
  '/page/three': (context) => ScreenC(),
},

fist of all we have ScreenA():

class ScreenA extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Navigation with params'),
      ),
      body: Center(
        child:  ElevatedButton(
          child: Text('Click me!'),
          onPressed: () {
            Navigator.pushNamed(
              context,
              '/page/two',
              arguments: PageArguments(
                  id: 1,
                  title: "Example Title"
              ),
            );
          },
        ),
      ),
    );
  }
}

and destination page as ScreenB() is:

class ScreenB extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final arguments = ModalRoute.of(context)!.settings.arguments;

    /* getting currect route name */
    print(ModalRoute.of(context)!.settings.name);

    /* getting NULL arguments */
    print(arguments);

    return Scaffold();
  }
}

class PageArguments{
  final int id;
  final String title;
  PageArguments({required this.id, required this.title});
}

flutter.dev/docs/cookbook/navigation/navigate-with-arguments — Dinesh Nagarajan
– Dinesh Nagarajan, Commented Aug 14, 2021 at 5:43

Peter Koltai · Accepted Answer · 2021-08-14 06:48:53Z

3

It seems that Persistent Bottom Navigation Bar package does not pass correctly route information, it could be a bug. If you put a breakpoint in the build method of ScreenB, you will see that not only the argument is null, but route name is also wrong.

I tried in main.dart with onGenerateRoute and it worked for me this way:


  List<PersistentBottomNavBarItem> _navBarsItems() {
    return [
      PersistentBottomNavBarItem(
          title: 'Home',
          icon: Icon(Icons.home),
          routeAndNavigatorSettings: RouteAndNavigatorSettings(
              initialRoute: '/page/one',
              onGenerateRoute: (RouteSettings settings) {
                WidgetBuilder builder;
                // Manage your route names here
                switch (settings.name) {
                  case '/page/one':
                    builder = (BuildContext context) => ScreenA();
                    break;
                  case '/page/two':
                    builder = (BuildContext context) => ScreenB();
                    break;
                  default:
                    throw Exception('Invalid route: ${settings.name}');
                }
                return MaterialPageRoute(
                  builder: builder,
                  settings: settings,
                );
              })),
      PersistentBottomNavBarItem(title: 'Help', icon: Icon(Icons.help)),
    ];
  }

About casting the argument, I agree with the other answer.

edited Aug 14, 2021 at 6:48

answered Aug 14, 2021 at 6:41

Peter Koltai

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1 Comment

Peter Koltai Over a year ago

Welcome. About the bug (if it is a bug) you can contact the package author.

Dinesh Nagarajan · Accepted Answer · 2021-08-14 06:36:37Z

0

Main and MyApp for reference

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: ScreenA(),
      routes: {
        '/page/one': (context) => ScreenA(),
        '/page/two': (context) => ScreenB(),
      },
    );
  }
}

Update ClassB with below code no modification required in ClassA

class ScreenB extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final arguments =
        ModalRoute.of(context)!.settings.arguments as PageArguments;

    print(ModalRoute.of(context)!.settings.name);
    print(arguments.id);
    print(arguments.title);
    print("------");

    return Scaffold();
  }
}

Key update:

Typecasting the argument.

final arguments =
    ModalRoute.of(context)!.settings.arguments as PageArguments;

Console log:

edited Aug 14, 2021 at 6:36

answered Aug 14, 2021 at 6:27

Dinesh Nagarajan

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2 Comments

Peter Koltai Over a year ago

It works with normal route definition, but not with persistent_bottom_nav_bar package.

Dinesh Nagarajan Over a year ago

I see since no reference to this package in question I was not aware of it. Thanks @PeterKoltai

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