Flutter. Get data from Navigator.of(context)

Question

I'm beginner of flutter and trying to make app now.

I have 3 pages.

First page has a ElevatedButton with Navigator.of(context).pushnamed('/second') Second page has a textEditingController, and the value of textEditingController is [int] Evalue. And I change screen by Navigator.of(context).pushReplacementNamed('/third, arguments : Evalue) Last page has a ElevatedButton to show the Evalue, and Change screen by Navigator.of(context).pop(Evalue) (I also got Evalue from Secondpage by ModalRoute.of(context)!.setting.arguments)

but when I come to first page, I don't get Evalue from Lastpage. I got Null value.

this is my code in first page. onPressed: () async {

final value = await Navigator.of(context).pushNamed('/second');

EveryTime I get null...

What is problem guys? Is there anyway to get data from third page to first page?

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
import 'database.dart';
import 'alphabeta.dart';

 void main() {
  runApp(MyApp());
  }

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
Future<Database> database = initDatabase();

return MaterialApp(
  title: 'NoiceAnalytics',
  theme: ThemeData(
    primarySwatch: Colors.blue,
  ),
  initialRoute: '/',
  routes: {'/': (context) => WidgetApp(database),
           '/first': (context) => first(database),
           '/second': (context) => second(database),
           '/third': (context) => third(database),
           '
          }
);

}

class WidgetApp extends StatefulWidget {
  final Future<Database> db;
  WidgetApp(this.db);

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

class _WidgetApp extends State<WidgetApp> {

  @override
  Widget build(BuildContext context) {
    database? db4;
    return Scaffold(
      body: Container(
        child: Center(
          child: Column(
              children: <Widget>[
                Padding(
                    padding: EdgeInsets.all(15),
                    child: SizedBox(width: 250, height: 80,
                        child: ElevatedButton(
                          child: Text(
                            'Noise', style: TextStyle(fontSize: 20),),
                          onPressed: () async {

                            final db3 = await Navigator.of(context).pushNamed('/second');
                            },
                      style: ElevatedButton.styleFrom(
                          shape: RoundedRectangleBorder(
                              borderRadius: BorderRadius.circular(20))),
                    )
                )
            ),
}

class second extends StatefulWidget {
  final Future<Database> db;
  second(this.db);

  @override
  State<StatefulWidget> createState() => _second();
}

class _second extends State<Backgroundnoise>{
  TextEditingController? bgnController;
  TextEditingController? measuretimeController;
  

  @override
  void initState(){
    super.initState();
    bgnController = new TextEditingController();
    measuretimeController = new TextEditingController();
    
  }

  @override
  Widget build(BuildContext context){

    return Scaffold(
      body: Container(
        child: Center(
            child: SingleChildScrollView(scrollDirection: Axis.vertical,
              child: Column(
              children: <Widget>[
              Padding(
                padding: EdgeInsets.only(top: 100 ,bottom: 15),
                child: Text('Background', style: TextStyle(fontSize: 20)),
              ),
              Padding(
                  padding: EdgeInsets.all(15),
                  child: SizedBox(width: 250, height: 80,
                      child: TextField(
                        controller: bgnController,
                        decoration: InputDecoration(labelText: 'enter the value', hintText: 'Ex)80.5'),
                        keyboardType: TextInputType.number,
                      )
                  )
              ),
              Padding(
                padding: EdgeInsets.all(15),
                child: Text('Time', style: TextStyle(fontSize: 20)),
              ),
              padding: EdgeInsets.all(15),
                  child: SizedBox(width: 250, height: 80,
                      child: TextField(
                        controller: measuretimeController,
                        decoration: InputDecoration(labelText: 'enter the value', hintText: 'Ex)80.5'),
                        keyboardType: TextInputType.number,
                      )
                  )
              ),
              Padding(
                padding: EdgeInsets.all(15),
                child: SizedBox(width: 250, height: 80,
                  child: ElevatedButton(
                    child: Text('result', style: TextStyle(fontSize: 20),), onPressed: (){
                      database db1 = database(
                        bgn: bgnController!.value.text,
                        measuretime: measuretimeController!.value.text,
                       
Navigator.of(context).pushReplacementNamed('/third', arguments: db1);
                        },
                        style: ElevatedButton.styleFrom(shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(50))),
                      ),
                    ),
                  )
                ],
                mainAxisAlignment: MainAxisAlignment.center,
                ),
              ),
            ),
          ),
        );
      }
    }

class third extends StatefulWidget {
  final Future<Database> db;
  third(this.db);

  @override
  State<StatefulWidget> createState() => _third();
}

class _third extends State<Calculation> {

  @override
  Widget build(BuildContext context) {
    final database db2 = ModalRoute.of(context)!.settings.arguments as database;

    return Scaffold(
        body: Container(
            child: Center(
                    child: Column(children: <Widget>[
                      Padding(
                      padding: EdgeInsets.only(top: 15 ,bottom: 15),
                      child: Text('S.sound', style: TextStyle(fontSize: 20)),
                      ),
                      Padding(
                      padding: EdgeInsets.all(15),
                        child: SizedBox(width: 250, height: 80,
                          child: ElevatedButton(
                            child: Text(db2.bgn.toString(), style: TextStyle(fontSize: 20),),
                                    onPressed: () {},
                                    style: ElevatedButton.styleFrom(
                                    shape: RoundedRectangleBorder(
                                    borderRadius: BorderRadius.circular(50))),
                       ),
                      ),
                     ),
                      Padding(
                        padding: EdgeInsets.all(15),
                          child: Text('Level', style: TextStyle(fontSize: 20)),
                  ),
                      Padding(
                        padding: EdgeInsets.all(15),
                          child: SizedBox(width: 250, height: 80,
                            child: ElevatedButton(
                              child: Text(db2.measuretime.toString(), style: TextStyle(fontSize: 20),),
                                     onPressed: () {},
                                     style: ElevatedButton.styleFrom(
                                     shape: RoundedRectangleBorder(
                                     borderRadius: BorderRadius.circular(50))),
                          ),
                        ),
                      ),
                      Padding(
                          padding: EdgeInsets.only(top: 30),
                          child:
                          Row(children: <Widget>[
                            Padding(
                            padding: EdgeInsets.all(5),
                            child:
                              SizedBox(width: 200, height: 80,
                                child: ElevatedButton(
                                  child: Text('Save and Quit', style: TextStyle(fontSize: 20),),
                                  onPressed: (){

                                

Navigator.of(context).pop(db2);
                                  },
                                  style: ElevatedButton.styleFrom(
                                    shape: RoundedRectangleBorder(
                                    borderRadius: BorderRadius.circular(50)))
                                )
                              )
                            ),
                          ],mainAxisAlignment: MainAxisAlignment.center
                      )
                      )

                        ],
                      mainAxisAlignment: MainAxisAlignment.center,
                    ),

                    )
                    )
                    );
  }
}

and where database.dart is

class database{
  int? id;
  String? bgn;
  String? measuretime;

  database({this.id, this.bgn ,this.measuretime});

  Map<String, dynamic> toMap(){
    return{
      'id': id, 'bgn': bgn, 'measuretime': measuretime
    };
  }
}

Answer 1

I think your mistake is how you retrieve your value from the new screen you pushed.

Currently, from what I understood, you're using:

final value = await Navigator.of(context).pushNamed('/second');

which indeed, will give you a null value.

You need to use the settings.argument in the new screen. ModalRoute.of(context)!.settings.arguments

You can find more about it here:
https://docs.flutter.dev/cookbook/navigation/passing-data https://docs.flutter.dev/cookbook/navigation/navigate-with-arguments