How to fix WillPopScope() not working for me

Just check out this answer and let me know if it works:

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:flutter/services.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(primarySwatch: Colors.amber),
      home: SecondPage(),
    );
  }
}

class LoginPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        child: Center(
            child: RaisedButton(
          child: Text('Move to second page after Login'),
          onPressed: () async {
            SharedPreferences preferences =
                await SharedPreferences.getInstance();

            preferences.setBool("islogin", true);
            // this will remove the login page after routing to the second page and then the stack will have only one page that is second page.
           // so later you can use the willpopscape 
            Navigator.pushAndRemoveUntil(
                context,
                MaterialPageRoute(builder: (context) => SecondPage()),
                ModalRoute.withName("/Home"));
          },
        )),
      ),
    );
  }
}

class SecondPage extends StatefulWidget {
  @override
  _SecondPageState createState() => _SecondPageState();
}

class _SecondPageState extends State<SecondPage> {
  @override
  void initState() {
    check_login();
    
    super.initState();
  }

  Future check_login() async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    if (preferences.getBool("islogin") == null)

    //This above if statement will check if the parameter islogin is null then redirect to the login screeen
    // else if the value is not null then i will not enter the if statement
      setState(() {
        Navigator.of(context).push(MaterialPageRoute(
          builder: (context) => LoginPage(),
        ));
      });
  }

  Future<bool> _onWillPop() async {

    // This dialog will exit your app on saying yes
    return (await showDialog(
          context: context,
          builder: (context) => new AlertDialog(
            title: new Text('Are you sure?'),
            content: new Text('Do you want to exit an App'),
            actions: <Widget>[
              new FlatButton(
                onPressed: () => Navigator.of(context).pop(false),
                child: new Text('No'),
              ),
              new FlatButton(
                onPressed: () => Navigator.of(context).pop(true),
                child: new Text('Yes'),
              ),
            ],
          ),
        )) ??
        false;
  }

  @override
  Widget build(BuildContext context) {
    return WillPopScope(
      onWillPop: _onWillPop,
      child: Scaffold(
        appBar: new AppBar(
          title: Text(
            "Home",
            style: new TextStyle(color: Colors.white),
          ),
          actions: <Widget>[
            FlatButton(
                onPressed: () async {
                   SystemNavigator.pop();
                },
                child: Text(
                  "Logout",
                  style: TextStyle(color: Colors.white, fontSize: 16.0),
                ))
          ],
        ),
      ),
    );
  }
}

Here is answer example_page code

class exmp extends StatefulWidget {
@override
_exmpState createState() => _exmpState();
}

class _exmpState extends State<exmp> {
@override
Widget build(BuildContext context) {
return Scaffold(
  appBar: AppBar(
    title: Text("example"),
  ),
  body: Column(
    children: <Widget>[
      Center(
        child: RaisedButton(onPressed: () {
          Navigator.of(context).pushAndRemoveUntil(
              MaterialPageRoute(
                builder: (context) => my_example(),
              ),
              (route) => false);
        }),
      )
    ],
  ),
);
}
}

And this is my second page my_example

class my_example extends StatelessWidget {
 @override
 Widget build(BuildContext context) {
  return MaterialApp(
  theme: ThemeData(primarySwatch: Colors.amber),
  home: my_examp(),
);
 }
}

 class my_examp extends StatefulWidget {
  @override
  _my_exampState createState() => _my_exampState();
 }

class _my_exampState extends State<my_examp> {
Future<bool> onbackpress() async{
return true;
}

@override
Widget build(BuildContext context) {
return WillPopScope(
  onWillPop: onbackpress,
  child: Scaffold(
    appBar: AppBar(
      title: Text("my_eaxmple"),
    ),
  ),
);
}
}

The problem was i am pushing another page from my main page but i forget to remove first page for that i used the Navigator.of(context).pushAndRemoveUntil( MaterialPageRoute(builder: (context) => my_example()(route) => false); to remove the main page before navigate to another page

This is how you should use

Future<bool> _willPopCallback() async {
    // await Show dialog of exit or what you want
    // then
    return true; //  
}


//then use in the build like
WillPopScope(child: new Scaffold(), onWillPop: _willPopCallback)

I resolved this error as in my case I have a parent screen and in that, I have PageView. I was trying to call WillPopScope in one of my PageView and then I realized my parent have WillPopScope too.

That is why it is not calling WillPopScope of PageView

don't use on Scaffold(), wrap your MaterialApp as in the example

bool allowed = false;
return WillPopScope(
  onWillPop: () async {
    print('MJD POP TRYING TO GET BACK from login Page');
    return Future.value(allowed);
  },
  child: MaterialApp(
    title: 'Your App Title',
    theme: ThemeData(
      primarySwatch: Colors.blue,
    ),
    home: const MyLoginPage(title: 'Login Page'),
  ),
);