flutterconfigglobalassets

Flutter application hangs when calling await rootBundle.loadString(...) from main()


I found this answer about storing global configuration into globals.dart.

How can I load configuration into it from assets/config.json?

I've tried like this:

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'dart:convert';
import 'globals.dart' as globals;

void main() async {
  globals.config = jsonDecode(await rootBundle.loadString('assets/config.json'));
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  ...
}

The application starts with a white screen. Nothing happens, no errors. I guess that await rootBundle.loadString(...) causes the application to hang.


Solution

  • You can copy paste run full code below
    You need to add WidgetsFlutterBinding.ensureInitialized() in main()
    without this line will produce white screen

    globals.dart

    Map<String, dynamic> config = {};
    

    config.json

    {    
        "id": "1",
        "name": "abc"
    }
    

    code snippet

    void main() async{
          WidgetsFlutterBinding.ensureInitialized();
          globals.config = jsonDecode(await rootBundle.loadString('assets/config.json'));
          runApp(MyApp());
        }
    

    pubspec.yaml

    assets:
      - assets/
    

    working demo

    enter image description here

    full code

    import 'package:flutter/material.dart';
    import 'package:flutter/services.dart';
    import 'dart:convert';
    import 'globals.dart' as globals;
    
    void main() async{
      WidgetsFlutterBinding.ensureInitialized();
      globals.config = jsonDecode(await rootBundle.loadString('assets/config.json'));
      runApp(MyApp());
    }
    
    class MyApp extends StatelessWidget {  
      @override
      Widget build(BuildContext context) {
        return MaterialApp(
          title: 'Flutter Demo',
          theme: ThemeData(        
            primarySwatch: Colors.blue,
          ),
          home: MyHomePage(title: 'Flutter Demo Home Page'),
        );
      }
    }
    
    class MyHomePage extends StatefulWidget {
      MyHomePage({Key key, this.title}) : super(key: key);
    
      final String title;
    
      @override
      _MyHomePageState createState() => _MyHomePageState();
    }
    
    class _MyHomePageState extends State<MyHomePage> {
      int _counter = 0;
    
      void _incrementCounter() {
        setState(() {     
          _counter++;
        });
      }
    
      @override
      Widget build(BuildContext context) {    
        return Scaffold(
          appBar: AppBar(        
            title: Text(widget.title),
          ),
          body: Center(        
            child: Column(         
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Text(globals.config["id"]),
                Text(globals.config["name"]),
                Text(
                  'You have pushed the button this many times:',
                ),
                Text(
                  '$_counter',
                  style: Theme.of(context).textTheme.headline4,
                ),
              ],
            ),
          ),
          floatingActionButton: FloatingActionButton(
            onPressed: _incrementCounter,
            tooltip: 'Increment',
            child: Icon(Icons.add),
          ), 
        );
      }
    }