How to call method from another class in Flutter(Dart)?

Question

I have created an Homepage and from that user can sign in for the app and in the next screen user can see their profile info(Only profile name) and under that their is signOut button. User can signOut from the app using signOut button.But it's not working for me.

I want to call signOut method from main.dart by pressing signOut button in details.dart(both the classes are in different file)

But when i press signOut Button in details.dart nothing happens!

And code is given below:

main.dart

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:google_sign_in/google_sign_in.dart';
import 'details.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      debugShowCheckedModeBanner: false,
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  MyHomePageState createState() => MyHomePageState();
}

class MyHomePageState extends State<MyHomePage> {
  final FirebaseAuth firebaseAuth = FirebaseAuth.instance;
  final  GoogleSignIn googleSignIn = GoogleSignIn();
  static bool _LoginButton = true;

  void signOut(){
    googleSignIn.signOut();
    setState((){
      _LoginButton = true;
    });
    print(_LoginButton);
    print("User Signed Out");
  }

  Future<FirebaseUser> _signIn() async{
    if(_LoginButton==true){
      setState((){
        _LoginButton=false;
      });
      GoogleSignInAccount googleSignInAccount = await googleSignIn.signIn();
      GoogleSignInAuthentication googleSignInAuthentication = await googleSignInAccount.authentication;
      FirebaseUser firebaseUser = await firebaseAuth.signInWithGoogle(idToken: googleSignInAuthentication.idToken, accessToken: googleSignInAuthentication.accessToken);
      print("Username is "+firebaseUser.displayName);
      setState((){
        _LoginButton = true;
      });
      Navigator.push(context, MaterialPageRoute(builder: (context) => details(firebaseUser.displayName,signOut)));

      return firebaseUser;
    }
  }

  bool _LoginButtonBool(){
    return _LoginButton;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("Google auth with firebase"),),
      body: Center(
        child: _LoginButtonBool()?Container(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: <Widget>[
              MaterialButton(onPressed: _LoginButtonBool() ? () => _signIn().then((FirebaseUser firebaseuser ) =>print(firebaseuser)).catchError((e) => print(e)): null,
              child: Text("Login"),color: Colors.orange,),
            ],
          ),
        ):CircularProgressIndicator(backgroundColor: Colors.greenAccent.withOpacity(0.01),),
      ),
    );
  }
}

details.dart

import 'package:flutter/material.dart';
import 'package:flutter_auth/main.dart';

class details extends StatelessWidget {
  String name;
  final Function callback;
  details(this.name,this.callback);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body:Center(child: Column(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: <Widget>[
          Text(name),
          MaterialButton(onPressed: () => callback,
          child: Text("Log out"),color: Colors.orange),
        ],
      ),),
    );
  }
}

Have you tried using a Callback? https://stackoverflow.com/questions/51029655/call-method-in-one-stateful-widget-from-another-stateful-widget-flutter — Alberto Méndez, Sep 28 '18 at 07:10
I tried using Callback but i am getting an error says "The expression here has a type of 'void', and therefore cannot be used. — yashthakkar2898, Sep 28 '18 at 07:47
Now i have fully updated my question. I Hope now you can understand what i'm trying to tell you. — yashthakkar2898, Sep 28 '18 at 12:41
in details.dart : change MaterialButton(onPressed: () => callback, to MaterialButton(onPressed: () => callback(), though this wont solve what you trying to do here, wont push you back to login screen. — anmol.majhail, Sep 28 '18 at 15:28
@anmol.majhail I don't know why but that worked for me!! thanks, and if you can explain it then it will be better for me. — yashthakkar2898, Sep 28 '18 at 16:23
@yash1173 to execute a function we need to call a function with parentheses. you were just referring the function not executing it. — anmol.majhail, Sep 28 '18 at 16:43

Osama Buzdar · Answer 1 · 2021-09-01T11:36:00.190

It is simple let me explain with an example

class Animals
{
  var animalList = ['dog','cat','cow'];

  // function for printing the list of animals

  void animalListPrinter(){
    for(var animal in animalList){
        print(animal);

     }
  }
}

Calling the above function to another class

class ShowingAnimalList extends StatelessWidget {
     final Animals ani= new Animals();
     @override
     Widget build(BuildContext context) {
       return GestureDetector(
         onTap:()=> ani.animalListPrinter(),
       );
  }
}

You can call any Widget with this from the parent class

score 12 · Accepted Answer · edited Apr 02 '19 at 09:11

You must be careful with what you are trying to do because you might be accessing a page/widget that is not mounted. Imagine you do a pushReplacement(new MaterialPageroute(...)). The previous page is no longer available in the tree so you can't access it nor any of its methods.

Unless you have a clear parent child relationship in your tree, you should abstract away your logic to external or business logic classes. Thus you are sure that you are calling active instances of your classes.

Here is an example of what you could use passing around the Business object. It would be even better if you use other patterns like BLOC, ScopedModel, Streams, etc. But for the sake of simplicity I think this should be enough.

import "package:flutter/material.dart";

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

class Logic {
  void doSomething() {
    print("doing something");
  }
}

class MyApp extends StatelessWidget {
  final Logic logic;

  MyApp(this.logic);

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new HomePage(widget.logic),
    );
  }
}

class HomePage extends StatelessWidget {
  final Logic logic;

  HomePage(this.logic);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: FlatButton(
          onPressed: () { Navigator.of(context).pushReplacement(
             MaterialPageRoute(
               builder: (context) => AnotherPage(logic),
             ))},
          child: Text("Go to AnotherPage"),
        ),
      ),
    );
  }
}

class AnotherPage extends StatelessWidget {
  final Logic logic;

  AnotherPage(this.logic);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: FlatButton(
          onPressed: logic.doSomething,
          child: Text("Press me"),
        ),
      ),
    );
  }
}

If you still want to call a function in the other Page and you are sure the page is mounted (you have done a push instead of a pushReplacement) you could do the following. (handle with care)

class HomePage extends StatelessWidget {

  HomePage();

  void onCalledFromOutside() {
    print("Call from outside");
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
    child: FlatButton(
          onPressed: () { Navigator.of(context).push(
             MaterialPageRoute(
               builder: (context) => AnotherPage(onCalledFromOutside),
             ))},
          child: Text("Go to AnotherPage"),
        ),
      ),
    );
  }
}

class AnotherPage extends StatelessWidget {
  final Function callback

  AnotherPage(this.callback);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
    child: FlatButton(
           onPressed: callback,
           child: Text("Press me"),
        ),
      ),
    );
  }
}

Well, you can't pass arguments to the route itself, but you can pass arguments to the constructor of the widget you are building (like the bloc param above) o use the `RouteSettings` as @rémi-rousselet suggests in https://stackoverflow.com/questions/47419908 — chemamolins, Jan 29 '19 at 07:21

score 6 · Answer 3 · answered May 01 '21 at 16:27

6

We can access it easily just like below.

className().MethodName(),

answered May 01 '21 at 16:27

Gayan Chinthaka

389
5
4

score 1 · Answer 4 · answered Aug 25 '20 at 23:45

you can create another logout() function and give context of home to push back to sign in screen/home screen , works for me as :

      logout() async {
        await googleSignIn.signOut();
        Navigator.push(context, MaterialPageRoute(builder: (context) => Home()));
      }

score 0 · Answer 5 · answered Sep 28 '18 at 07:04

0

Import HomePage class in DetailsPage and make a new instance out of it, then call the method you want if it's a public one.

answered Sep 28 '18 at 07:04

Alex Lindroos

19
4

i am sure it will not work as i cannot create an object of it. – yashthakkar2898 Sep 28 '18 at 07:56

Tanvirul islam · Answer 6 · 2021-06-12T07:05:24.817

We can take help instance Make instance given below

var objectName = new ClassName(<constructor_arguments>)

Note: We can use an empty constructor like this example.

 class Student{
void female(){
print('This is female method');
}
void male(){
print('This is malemethod'); }
}

step1: var _instance1 = new Student(); here empty constructor it dos't matter.

step2: _instance1.male(); Call method _instance1 what we want.

How to call method from another class in Flutter(Dart)?

6 Answers6

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