Could not find a generator for r

记录一个初学时出现的错误。
使用了注册路由的方式进行了页面注册
在myApp中的 MaterialApp中进行注册

return MaterialApp(
      *** 无关代码***
      //注册路由
      routes: <String, WidgetBuilder>{
        //登录相关路由
        SplashScreen.routeName: (BuildContext context) =>  SplashScreen(),
        SignInPage.routeName: (BuildContext context) =>  SignInPage(),
        //主页面路由
        MainNavBarPage.routeName:(BuildContext context) => MainNavBarPage (),
      },
      initialRoute: SPLASH_SCREEN,
    );

后面又使用了 MaterialApp包裹了其他Widget

class MainNavBarPage extends StatelessWidget {
  static const routeName = MAIN_NAV_BAR;
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: FluidNavBarDemo(),
    );
  }
}

由于再次使用的MaterialApp已经替换了之前的，所以之前注册的路由已经全部失效。
因此出现以下错误

Could not find a generator for route ** in the _WidgetsAppState.

删除第二个MaterialApp即可

class MainNavBarPage extends StatelessWidget {
  static const routeName = MAIN_NAV_BAR;
  @override
  Widget build(BuildContext context) {
    return FluidNavBarDemo();
  }
}

参考https://stackoverflow.com/questions/49132299/could-not-find-a-generator-for-route