type 'Null' is not a subtype of type 'Map<String, dynamic>' in type cast

Question

i have this error while i want to create dynamic navigation with multiple pages.. here is code below..

import 'package:flutter/material.dart';
import 'screens/locations/locations.dart';
import 'screens/location_detail.dart';

 const LocationsRoute = "/";
 const LocationDetailRout = '/location_detail';

 class App extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
   return MaterialApp(
    onGenerateRoute: _routes(),
);

}

 RouteFactory _routes() {
   return (settings) {
   // final Map<String, dynamic> arguments = settings.arguments;
    final arguments = settings.arguments as Map<String, dynamic>;
    Widget screen;
    switch (settings.name) {
      case LocationsRoute:
      screen = Locations();
      break;
      case LocationDetailRout:
      screen = LocationDetail(arguments['id']);
  }
};

}

thanhbinh84 · Accepted Answer · 2021-12-15 04:52:04Z

4

Quick fix

Map arguments = (settings.arguments??{}) as Map;

answered Dec 15, 2021 at 4:52

thanhbinh84

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Syed Zulqarnain · Accepted Answer · 2021-06-15 14:44:02Z

According to flutter official documentation at https://flutter.dev/docs/cookbook/navigation/navigate-with-arguments The onGenerateRoute() function creates the correct route based on the given RouteSettings.

So the thing that we have been doing wrong was that we were looking for arguments for every route in the main block (outside of switch statements), but only LocationDetailRoute route has the arguments that's why we were getting null for all other routes.

RouteFactory _routes() {
    return (settings) {
      Widget screen;
      switch (settings.name) {
        case LocationsRoute:
          screen = Locations();
          break;
        case LocationDetailRoute:
          // Correct Place for this Statement
          final arguments = settings.arguments as Map<String, dynamic>; 
          screen = LocationDetails(arguments['id']);
          break;
        default:
          return null;
      }
      // return MaterialPageRoute(builder: (BuildContext context) => screen);
      return MaterialPageRoute(builder: (BuildContext context) => screen, settings: settings);
    };
  }

puelo · Accepted Answer · 2021-05-03 22:06:09Z

0

The arguments of RouteSettings can be Null and this is why you are seeing the error here final arguments = settings.arguments as Map<String, dynamic>; . You are basically trying to cast Null to a Map. Also i am not sure if this is intentional, but your inner function (the actual RouteFactory) is not returning a Route in any case.

answered May 3, 2021 at 22:06

puelo

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2 Comments

Ahmed Jaad Over a year ago

then how should i fixed it

puelo Over a year ago

You should probably only extract the arguments if you expect the route to have arguments. Or just check if arguments are Null before extracting (although this would crash further down when you try to access arguments)

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