Another exception was thrown: Could not find a generator for route RouteSettings("/routename", null) in the _WidgetsAppState

Question

I just started learning flutter. I was creating a guide app for a game. And I encountered this error.

Another exception was thrown: Could not find a generator for route RouteSettings("/bo3morgmap", null) in the _WidgetsAppState.

---

main.dart

// ignore_for_file: prefer_const_constructors, prefer_const_literals_to_create_immutables

import 'package:flutter/material.dart';
import 'pages/blackops3/blackops3.dart';
import 'pages/blackops3/morgmap.dart';

void main() {
   runApp(MainApp(),);
}
class MainApp extends StatelessWidget {
  const MainApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text("Zombies Assistants"), backgroundColor: Color.fromARGB(255, 107, 21, 204), centerTitle: true),
        drawer: Builder(
          builder: (context) {
            return Drawer(
              child: Column(
                children: [
                  DrawerHeader(child: Icon(Icons.games, size: 64,)),
                  ListTile(
                    leading: Icon(Icons.home),
                    title: Text("Main Menu"),
                    onTap: () {
                      Navigator.popAndPushNamed(context, '/main');
                    },
                  ),
                  ListTile(
                    leading: Icon(Icons.gamepad),
                    title: Text("Black Ops 3"),
                    onTap: () {
                      Navigator.popAndPushNamed(context, '/blackops3');
                    },
                  ),
                ],
              ),
            );
          }
        ),
      ),
      routes: { 
        '/blackops3': (context) => blackops3(),
        '/main': (context) => MainApp(),
        '/bo3morgmap': (context) => morgmap(),
      },
      theme: ThemeData(
        useMaterial3: true,
      ),
    );
  }
}

---

blackops3.dart

import 'package:flutter/material.dart';
// ignore: unnecessary_import
import 'package:flutter/widgets.dart';
// ignore: camel_case_types
// ignore_for_file: prefer_const_constructors, prefer_const_literals_to_create_immutables
// ignore: camel_case_types
class blackops3 extends StatelessWidget {
  const blackops3({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          leading: IconButton(icon: Icon(Icons.arrow_back),
          onPressed: () {
           Navigator.of(context).pop();}
          ),
          title: const Text("Black Ops 3"), backgroundColor: Color.fromARGB(255, 107, 21, 204), centerTitle: true,
        ),
        body: Builder(
          builder: (context) {
            return Column(
              children: [
                Padding(
                  padding: const EdgeInsets.all(8.0),
                  child: Center(
                    child: ElevatedButton(
                      onPressed: () {Navigator.pushReplacementNamed(context, '/bo3morgmap');},
                      child: Text("Morg City Map"),
                    ),
                  ),
                ),
                Center(
                  child: ElevatedButton(onPressed: () {Navigator.pushReplacementNamed(context, '/bo3morgmap');},
                  child: Text("Train Signs Helper"),
                  ),
                ),
              ],
            );
          }
        ),
      ),
    );
  }
}

---

morgmap.dart

import 'package:flutter/material.dart';
// ignore: camel_case_types
// ignore_for_file: prefer_const_constructors, prefer_const_literals_to_create_immutables
// ignore: camel_case_types
class morgmap extends StatelessWidget {
  const morgmap({super.key});

  @override
  Widget build(BuildContext context){
      return Scaffold(
        appBar: AppBar(
          leading: IconButton(icon: Icon(Icons.arrow_back),
          onPressed: () {
           Navigator.of(context).pop();}
          ),
          title: const Text("Black Ops 3"), backgroundColor: Color.fromARGB(255, 107, 21, 204), centerTitle: true,
      ),
      body: Builder(
          builder: (context) {
            return Column(
              children: [
                Text("Im working")
              ],
            );
          }
        ),
    );
  }
}

---

I also think I'm doing things wrong.

.....
body: Builder(
          builder: (context) {
            return Column(
              children: [
                Padding(
                  padding: const EdgeInsets.all(8.0),
                  child: Center(
                    child: ElevatedButton(
                      onPressed: () {Navigator.pushReplacementNamed(context, '/bo3morgmap');},
                      child: Text("Morg City Map"),
                    ),
                  ),
                ),
                Center(
                  child: ElevatedButton(onPressed: () {Navigator.pushReplacementNamed(context, '/bo3morgmap');},
                  child: Text("Train Signs Helper"),
                  ),
                ),
              ],
            );
          }
        ),
.....

Am I supposed to put the 2 elevated buttons in the same child? I don't think that's possible.

I want the navigator to navigate through morgmap. I tried adding () => (I saw it on another post) but it still didn't work. And I don't think that is the problem. Even if I add it it still doesn't navigates through.

Answer 1

Solution

Your issue likely is due to instantiating MaterialApp twice.

1. Once in main.dart (encouraged, keep this one),
2. but also in blackops3.dart (remove this one).

See MaterialApp as the root component/entry point of your application, and you should only need to instantiate it once per app. Read more about MaterialApp here.

So: remove the MaterialApp inside blackops3.dart, like so:

class blackops3 extends StatelessWidget {
  const blackops3({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold( ... ); // <-- Here we've removed the wrapping `MaterialApp`
  }
}

Why the issue occurs

When you instantiate MaterialApp inside blackops3.dart you create a new app scope, in which your routes (which you declared in the top-most MaterialApp) no longer exist.

Therefore your call to

Navigator.pushReplacementNamed(context, '/bo3morgmap');

Throws an exception, since there is no defined route for the path you've provided.