flutter 路线显示找不到路线 RouteSettings 的生成器

Question

When I am building a flutter app there is three Screens, Screen A, Screen B, Screen C. When clicking on button it redirects to next screen. So it is redirecting A to B. But not redirecting B to C. I don't know the reason. It showing error. It showing the error is

Could not find a generator for route RouteSettings("/extractArguments1", Instance of 'ScreenArguments') in the _WidgetsAppState.

My code shown below

    import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      routes: {
        '/extractArguments': (context) => ExtractArgumentsScreen(),
        '/extractArguments1': (context) => ExtractArgumentsScreen1(),
      },
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {




  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(

        title: Text("A"),
      ),
      body: Center(
        child: new RaisedButton(onPressed: (){
          Navigator.pushNamed(context, "/extractArguments",arguments: ScreenArguments("title", "message"));
        },
        child: new Text("Click"),),

      ),

    );
  }
}


class ScreenArguments {
  final String title;
  final String message;

  ScreenArguments(this.title, this.message);
}

class ExtractArgumentsScreen extends StatelessWidget{

ExtractArgumentsScreen({
    Key key,
    @required this.title,
    @required this.message,
  }): super(key: key);

  final String title;
  final String message;

  @override
  Widget build(BuildContext context) {

    final ScreenArguments args = ModalRoute.of(context).settings.arguments;


    // return new Scaffold(
    //   appBar: new AppBar(title: new Text('args.title')),
    //     body: new Center(child: new Text('args.message'),),
    // );

    return MaterialApp(
      title: 'Flutter Demo',

      home: MyHomePage1(title: 'Flutter Demo Home Page'),
    );


  }



}


class MyHomePage1 extends StatefulWidget {
  MyHomePage1({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePage1State createState() => _MyHomePage1State();
}

class _MyHomePage1State extends State<MyHomePage1> {




  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(

        title: Text("B"),
      ),
      body: Center(
        child: new RaisedButton(onPressed: (){
          Navigator.pushNamed(context, "/extractArguments1",arguments: ScreenArguments("title", "message"));
        },
        child: new Text("Click"),),

      ),

    );
  }
}

class ExtractArgumentsScreen1 extends StatelessWidget{

ExtractArgumentsScreen1({
    Key key,
    @required this.title,
    @required this.message,
  }): super(key: key);

  final String title;
  final String message;

  @override
  Widget build(BuildContext context) {

    final ScreenArguments args = ModalRoute.of(context).settings.arguments;


    // return new Scaffold(
    //   appBar: new AppBar(title: new Text('args.title')),
    //     body: new Center(child: new Text('args.message'),),
    // );

    return MaterialApp(
      title: 'Flutter Demo',

      home: MyHomePage2(title: 'Flutter Demo Home Page'),
    );


  }



}


class MyHomePage2 extends StatefulWidget {
  MyHomePage2({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePage2State createState() => _MyHomePage2State();
}

class _MyHomePage2State extends State<MyHomePage2> {




  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(

        title: Text("C"),
      ),
      body: Center(
        child: new RaisedButton(onPressed: (){
      //   Navigator.pushNamed(context, "/extractArguments1",arguments: ScreenArguments("title", "message"));
        },
        child: new Text("Click"),),

      ),

    );
  }
}

And the complete error is

     The following assertion was thrown while handling a gesture:
  I/flutter (23854): Could not find a generator for route RouteSettings("/extractArguments1", Instance of
  I/flutter (23854): 'ScreenArguments') in the _WidgetsAppState.
  I/flutter (23854): Generators for routes are searched for in the following order:
  I/flutter (23854):  1. For the "/" route, the "home" property, if non-null, is used.
  I/flutter (23854):  2. Otherwise, the "routes" table is used, if it has an entry for the route.
  I/flutter (23854):  3. Otherwise, onGenerateRoute is called. It should return a non-null value for any valid route not
  I/flutter (23854): handled by "home" and "routes".
  I/flutter (23854):  4. Finally if all else fails onUnknownRoute is called.
  I/flutter (23854): Unfortunately, onUnknownRoute was not set.

Please help me to find the issue.

Answer 1

The problem is when you are calling:

 Navigator.pushNamed(context, "/extractArguments1",arguments: ScreenArguments("title", "message"));

You are passing the arguments in a named route, but you are nowhere accepting the arguments. You need to extract the arguments inside an onGenerateRoute() function and pass them to a widget. The onGenerateRoute() function creates the correct route based on the given RouteSettings. So what you can do is add onGenerateRoute() function inside your material app as follows:

 onGenerateRoute: (settings) {

    if (settings.name == "/extractArguments1") {

      final ScreenArguments args = settings.arguments;

      // Extract the required data from the arguments and
      // pass the data to the correct screen.
      return MaterialPageRoute(
        builder: (context) {
          return ExtractArgumentsScreen1(
            title: args.title,
            message: args.message,
          );
        },
      );
    }
  },

This function will handle the arguments correctly pass them to respective screen screen. For reference see official documentation .