CODEWITHSUNDEEP
flutterrouternavigatordart-null-safety
Jan Smitka
Jan Smitka

Reputation: 109

Passing arguments in navigator flutter

I am facing a problem in my app after updating to new version of flutter (null safety).

i have router and navigator set up as described in code below, when i run the app the router returns error: "type Null is not a subtipe of type ScreenArgs in type cast"

this is probably caused by not initializing any instance of class ScreenArgs, but i can't figure out where is the error.

Layout:

final _navigatorKey = GlobalKey<NavigatorState>();
...

 return Scaffold(
  backgroundColor: Colors.white,
  body: Navigator(
   key: _navigatorKey,
   initialRoute: profileRoute,
    onGenerateRoute: generateRoute,
   ),
   bottomNavigationBar: navBar(),
  );

  void _onItemTapped(int index) {
    setState(() {
      _screenIndex = index;
    });
    switch (index) {
      case 0:
        _navigatorKey.currentState!.pushNamed(coursesRoute);
        break;
    }
  }

Router:

Route<dynamic> generateRoute(RouteSettings settings) {
  final args = settings.arguments as ScreenArgs;

  switch (settings.name) {
    ...
    case profileRoute:
      return PageTransition(
          child: const ProfileScreen(), type: PageTransitionType.fade);

    case coursesRoute:
      return PageTransition(
          child: CoursesScreen(
            entityId: args.entityId,
          ),
          type: PageTransitionType.fade);
    ...
  }
}

ScreenArgs:

class ScreenArgs {
  final String quizId;
  final String courseId;
  final String entityId;
  final numOfQuestions = numberOfQuestions;

  ScreenArgs(this.quizId, this.entityId, this.courseId);
}

i tried to initialize instance of ScreenArgs in Layout and pass it in the navigater as followed:

final args = ScreenArgs("","","");

Navigator(
   key: _navigatorKey,
   initialRoute: profileRoute,
    onGenerateRoute: (args) {generateRoute(args);}
   ),
   bottomNavigationBar: navBar(),
  );

or in the itemTapped switcher as follows:

switch (index) {
      case 0:
        _navigatorKey.currentState!.pushNamed(profileRoute, arguments: args);
        break;

but nothing worked and i got the same error message and i am stuck onto this for several hours. If anyone sees where i went wrong, please let me know, thanks in advance.

Upvotes: 0

Views: 819

Answers (1)

Jan Smitka
Jan Smitka

Reputation: 109

problem has been solved. The cause was initializing multiple GlobalKey and the statement that caused the error was

_navigatorKey.currentState!.pushNamed(profileRoute, arguments: args);

namely check

.currentState!.

moved GlobalKey declaration into global variables and used it for both navigator and locator of router and everything is working fine now.

Upvotes: 1

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