title: How to pass argument to route?
body: <p>I try to pass argument "_difficulty" from "First page" to "Second page" but i don't understand how to do this:
  This argument is a String and represent difficulty mode (easy, normal, hard)</p>
  
  <p><strong>First page:</strong> 
  When user click on button, OnPressed is called</p>
  
  <pre><code>onPressed: () {
     Navigator.pushNamed(context, '/gamepage', arguments: _difficulty);
  },
  </code></pre>
  
  <p><strong>Second page</strong>
  This call receive argument to show value</p>
  
  <pre><code> import 'package:flutter/material.dart';
  
   class GamePage extends StatelessWidget {    
    final String difficultyMode;
    GamePage(this.difficultyMode);
  
    @override
    Widget build(BuildContext context) {
  
      final GamePage args = ModalRoute.of(context).settings.arguments;
  
      return Scaffold(
        body:  new Container(
            child: SingleChildScrollView(
                child: Text(args.difficultyMode)
            )
        ),
      );
    }
  }
  </code></pre>
  
  <p><strong>In main.dart:</strong>
  I using onGenerateRoute: _getRoute,</p>
  
  <pre><code>Route _getRoute(RouteSettings settings) {
      switch (settings.name){
        case '/':
          return _buildRoute(settings, new Homepage());
        case '/credits':
          return _buildRoute(settings, new Credits());
        case '/gamepage':
          return _buildRoute(settings, new GamePage(diffculty));
        default:
          return null;
      }
    }
  </code></pre>