title: Navigator pass arguments with pushNamed
body: <p>Might have been asked before but I can't find it but how do you pass a arguments to a named route?</p>
  
  <p>This is how I build my routes</p>
  
  <pre><code>Widget build(BuildContext context) {
      return new Navigator(
        initialRoute: 'home/chooseroom',
        onGenerateRoute: (RouteSettings settings) {
          WidgetBuilder builder;
          switch (settings.name) {
            case 'home/chooseroom':
              // navigates to 'signup/choose_credentials'.
              builder = (BuildContext _) =&gt; new ChoosePage();
              break;
            case 'home/createpage':
              builder = (BuildContext _) =&gt; new CreateRoomPage();
              break;
            case 'home/presentation':
              builder = (BuildContext _) =&gt; new Presentation();
              break;
            default:
              throw new Exception('Invalid route: ${settings.name}');
          }
          return new MaterialPageRoute(builder: builder, settings: settings);
        },
      );
  </code></pre>
  
  <p>This is how you call it
  <code>Navigator.of(context).pushNamed('home/presentation')</code></p>
  
  <p>But what if my widget is <code>new Presentation(arg1, arg2, arg3)</code>?</p>