问通过Navigator()

EN

if(_currentPage.name == 'pages[0]') pageBuilds[0]

Navigator.onGenerateRoute was null, but the route named "/" was referenced 

/**
 * The RouteDelegate defines application specific behavious of how the router
 * learns about changes in the application state and how it responds to them. 
 * It listens to the RouteInformation Parser and the app state and builds the Navigator with
 * the current list of pages (immutable object used to set navigator's history stack).
 */

//ChangeNotifier for the listeners as they are handled there
//The popRoute is handled by 'PopNavigatorRouterDelegateMixin'
class RoutesDelegater extends RouterDelegate<RoutePath>
    with ChangeNotifier, PopNavigatorRouterDelegateMixin<RoutePath> {
  //This is the state of the navigator widget (in build method)
  GlobalKey<NavigatorState> get navigatorKey => GlobalKey<NavigatorState>();
  //RoutesDelegater()  : navigatorKey = GlobalKey<NavigatorState>();
  MyPage _currentPage;
  bool show404 = false; //checks if we show the 404 page

  List<MyPage> pages = [
    MyPage('ProjektListe'),
    MyPage('StudiListe'),
    MyPage('PRView'),
  ];

  List<Page> pageBuilds = [
    MaterialPage(key: ValueKey('Unknown'), child: UnknownScreen()),
    MaterialPage(key: ValueKey('Homepage'), child: MyFirstHomepage()),
    MaterialPage(key: ValueKey('OtherScreen'), child: OtherScreen()),
  ];

  //currentConfiguration detects changes in the route information
  //It helps complete the browser history and (IMPORTANT) makes the browser back and forward buttons work

  RoutePath get currentConfiguration {
    if (show404) {
      return RoutePath.unknown();
    }
    if (_currentPage == null) return RoutePath.home();
    //if not 404 or homepage it is some other page
    return RoutePath.details(pages.indexOf(_currentPage));
  }

  @override
  Widget build(BuildContext context) {
    return Navigator(
        key: navigatorKey,
        pages: //List.of(pageBuilds),
            [
          //pageBuilds[1],
          if (show404)
            pageBuilds[0]
          else if (_currentPage != null)
            pageBuilds[1]
        ],
        onPopPage: (route, result) {
          if (!route.didPop(result)) {
            return false;
          }
          _currentPage = null;
          show404 = false;
          //we are using Changenotifier
          notifyListeners();
          return true;
        });
  }

  void _handleTapped(MyPage page) {
    _currentPage = page;
    notifyListeners();
  }

  @override
  Future<void> setNewRoutePath(RoutePath path) async {
    //Handle the unknown path
    if (path.isUnknown) {
      show404 = true;
      _currentPage = null;
      return;
    }

    if (path.isDetailPage) {
      //Check if Path id is valid
      if (path.id.isNegative || path.id > pages.length - 1) {
        show404 = true;
        return;
      }
      _currentPage = pages[path.id];
    } else {
      //homepage will be shown
      _currentPage = null;
    }

    show404 = false;
  }
}

/*
* The RouteInformationParser takes the RouteInformation from RouteInformationProvider and
* parses it into a user-defined data type.
*/

class MyRoutesInformationParser extends RouteInformationParser<RoutePath> {
  @override
  Future<RoutePath> parseRouteInformation(
      RouteInformation routeInformation) async {
    //routeInformation is an object we get from the uri
    final uri = Uri.parse(routeInformation.location);
    // Handle '/' (Home Path)
    //Path segments are the segments seperated by /, if we don't have any we are on Home
    if (uri.pathSegments.length == 0) {
      return RoutePath.home();
    }

    //We have 2, as we have matchit/...
    if (uri.pathSegments.length == 2) {
      //If there is no 'matchit' in the first path segment the path is unknown
      if (uri.pathSegments.first != 'matchit') return RoutePath.unknown();
      //If we now have the correct first segment we can now handle the rest of the segment
      final remaining = uri.pathSegments.elementAt(1);
      final id = int.tryParse(remaining);
      //if it fails we return the unknown path
      if (id == null) return RoutePath.unknown();
      return RoutePath.details(id);
    }

    //Handling the unknown Path, e.g. user just typed anything in uri
    return RoutePath.unknown();
  }

  //THIS IS IMPORTANT: Here we restore the web history
  @override
  RouteInformation restoreRouteInformation(RoutePath path) {
    //Here we set the routeInformation which is used above, e.g. /404 for unknown page
    if (path.isUnknown) {
      return RouteInformation(location: '/404');
    }
    if (path.isHomePage) {
      return RouteInformation(location: '/');
    }
    //Any other page is handled here via /matchit/... <= the id of the path
    if (path.isDetailPage) {
      return RouteInformation(location: '/matchit/${path.id}');
    }
    //If none of the paths are hit
    return null;
  }
}

class RoutePath{
  final int id;
  final bool isUnknown;

  RoutePath.home()
      : id = null,
        isUnknown = false;

  //Details means here that it is any other side than Home or unknown
  RoutePath.details(this.id) : isUnknown = false;

  RoutePath.unknown()
      : id = null,
        isUnknown = true;

  //check if is on HomePage or other page, then either == null or != null
  //not needed for isInknown, as when unknown then = true as set above
  bool get isHomePage => id == null;
  bool get isDetailPage => id != null;
}

class Homepage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _HomepageState();
}

class _HomepageState extends State<Homepage> {
  //initialize the RouteDelegater and Information Parser to be unsed further down

  RoutesDelegater _routesDelegater = RoutesDelegater();
  MyRoutesInformationParser _myRoutesInformationParser =
      MyRoutesInformationParser();

/*
 * Relevant routing information for this build method:
 * We need to use the MaterialApp.router else we can't use routerDelegate and routeInformationParser.
 * Then we define the delegate and Information Parser (they are initiated above)
 */

  @override
  Widget build(BuildContext context) {
    return MaterialApp.router(
        title: 'MatchIT',
        routerDelegate: _routesDelegater,
        routeInformationParser: _myRoutesInformationParser,
        theme: ThemeData(primarySwatch: Colors.blue),
        debugShowCheckedModeBanner: false);
  }
}