flutter_global_variable_main.dart

import 'package:flutter/material.dart';
import 'package:scoped_model/scoped_model.dart';
import 'package:flutter_global_variable/scoped_models/main.dart';
import 'package:flutter_global_variable/pages/page2.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final MainModel _model = MainModel();

    return ScopedModel<MainModel>(
        model: _model,
        child: MaterialApp(
          title: 'Flutter Demo',
          theme: ThemeData(
            primarySwatch: Colors.blue,
          ),
          home: MyHomePage(title: 'Flutter Demo Home Page'),
        ));
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  Widget build(BuildContext context) {
    return ScopedModelDescendant<MainModel>(
        builder: (BuildContext context, Widget child, MainModel model) {
      return Scaffold(
        appBar: AppBar(
          title: Text(title),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'You have pushed the button this many times:',
              ),
              Text(
                '${model.count}',
                style: Theme.of(context).textTheme.display1,
              ),
              SizedBox(height: 10.0),
              RaisedButton(
                  padding: const EdgeInsets.all(8.0),
                  child: Text('Submit'),
                  onPressed: () {
                    Navigator.push(
                      context,
                      MaterialPageRoute<Page2>(
                          builder: (BuildContext context) => Page2()),
                    );
                  })
            ],
          ),
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            model.incrementCount();
          }, //_incrementCounter(_model),
          tooltip: 'Increment',
          child: Icon(Icons.add),
        ), // This trailing comma makes auto-formatting nicer for build methods.
      );
    });
  }
}