How to store a User id or "key" after login and access from anywhere in Flutter app?

Question

I am trying to determine the best way to store and access my Flutter app's User object after a login. There is no real authentication as of right now. So when the "user" logs in it just checks a json file for a dummy username and password. The only thing I want to know is what is the appropriate way to store and access my User id from anywhere in the app? I have been passing it as a route parameter every time the screen changes but that seems like overkill. What is the most appropriate way to do this? Just create a globals.dart file and add the user id as a variable?

Example of User in json:

{
    "id" : 5,
    "fName" : "John",
    "lName" : "Doe",
    "position" : "Software Developer",
    "username" : "jdoe",
    "password" : "jdoepass",
    "imageUrl": "assets/images/profile_pictures/profilePicture.png",
    "email" : "[email protected]",
    "location" : "Big Software Company"
}

Login.dart:

import 'package:flutter/material.dart';
import 'package:google_fonts/google_fonts.dart';
import '../utils/opWidgets.dart';
import '../utils/fetchJson.dart';
import '../../entities/User.dart';

/* Description: Login screen widget and functions to handle fetching user json */

class LoginPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _LoginPageState();
  }
}

class _LoginPageState extends State<LoginPage> {
  List<User> _userList = []; //used to represent the list items in the UI
  final userTxtController = TextEditingController();
  final passTxtController = TextEditingController();
  User _currentUser;
  bool _invalidUserMsgVisible = false;

  @override
  initState() {
    //initializes data before build() is called
    //Use this method to initialize data that will be displayed
    //initialize list items using function that fetches/converts json
    fetchUsers().then((value) {
      setState(() {
        _userList.addAll(value);
      });
    });
    super.initState();
  }

  @override
  void dispose() {
    //releases memory
    userTxtController.dispose();
    passTxtController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      resizeToAvoidBottomInset: false,
      body: GestureDetector(
        //Makes the keyboard collapse when the scaffold body is tapped
        onTap: () => FocusScope.of(context).unfocus(),
        child: _layoutDetails(),
      ),
    );
  }

  //This widget determines the layout of the widgets _logo() and _loginForm() based on the screen's orientation
  Widget _layoutDetails() {
    Orientation orientation = MediaQuery.of(context).orientation;

    if (orientation == Orientation.portrait) {
      return Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          _logo(),
          _loginForm(),
        ],
      );
    } else {
      return Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          _logo(),
          Container(
            width: MediaQuery.of(context).size.width / 1.8,
            height: MediaQuery.of(context).size.height,
            child: _loginForm(),
          ),
        ],
      );
    }
  }

  Widget _logo() {
    return Container(
      width: 225,
      child: Image.asset('assets/images/logos/OPNewLogo.png'),
    );
  }

  Widget _loginForm() {
    return Container(
      width: double.infinity,
      padding: EdgeInsets.all(20),
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Visibility(
            visible: _invalidUserMsgVisible,
            child: Text(
              'Username or password is invalid',
              style: GoogleFonts.montserrat(color: Colors.red, fontSize: 14),
            ),
          ),
          SizedBox(height: 5),
          Container(
            //margin: EdgeInsets.symmetric(horizontal: 10),
            width: 500,
            child: opTextField('Username', false, userTxtController),
          ),
          SizedBox(height: 20),
          Container(
            //margin: EdgeInsets.symmetric(horizontal: 10),
            width: 500,
            child: opTextField('Password', true, passTxtController),
          ),
          SizedBox(height: 20),
          Container(
            width: 500,
            height: 40,
            padding: EdgeInsets.symmetric(horizontal: 8),
            child: ElevatedButton(
              onPressed: () => _verifyLogin(
                userTxtController.text.toString().trim(),
                passTxtController.text.toString(),
              ),
              child: Text(
                'LOGIN',
                style: GoogleFonts.montserrat(
                  fontSize: 16,
                  letterSpacing: 1.5,
                  color: Colors.white,
                  fontWeight: FontWeight.w500,
                ),
              ),
              style: ElevatedButton.styleFrom(
                shape: RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(20),
                ),
                primary: Theme.of(context).accentColor,
                elevation: 3,
              ),
            ),
          ),
          SizedBox(height: 5),
          Container(
            width: 500,
            height: 40,
            padding: EdgeInsets.symmetric(horizontal: 8),
            child: ElevatedButton(
              onPressed: () => {
                Navigator.pop(context),
              },
              child: Text(
                'REGISTER',
                style: TextStyle(
                    fontSize: 16,
                    letterSpacing: 2.2,
                    color: Theme.of(context).shadowColor,
                    fontWeight: FontWeight.w500),
              ),
              style: ElevatedButton.styleFrom(
                shape: RoundedRectangleBorder(
                  borderRadius: BorderRadius.circular(20),
                  side: BorderSide(
                    color: Theme.of(context).primaryColorDark,
                  ),
                ),
                primary: Colors.white,
              ),
            ),
          ),
          Container(
            child: TextButton(
              autofocus: false,
              clipBehavior: Clip.none,
              child: Text(
                'Forgot Password',
                style: GoogleFonts.montserrat(
                  fontSize: 15,
                  color: Theme.of(context).shadowColor,
                  decoration: TextDecoration.underline,
                ),
              ),
              onPressed: () =>
                  Navigator.pushNamed(context, resetPasswordPageRoute),
            ),
          ),
        ],
      ),
    );
  }

  //Function to check the username and password input against the list of user objects
  void _verifyLogin(String username, String password) {
    bool _validUser = false;

    //Loop through fetched user objects and check for a match
    for (var user in _userList) {
      if (username == user.username && password == user.password) {
        _validUser = true;
        _currentUser = user; //Set the current user object
        break;
      }
    }
    //If a valid user was found, pop login screen and push home screen
    if (_validUser) {
      Navigator.popAndPushNamed(
        context,
        homePageRoute,
        arguments:
            _currentUser, //Pass the current user object to the home screen
      );
    } else {
      //if no valid user was found, make error message text visible
      setState(() {
        _invalidUserMsgVisible = true;
      });
    }
  }
}

Solution

you can use static and a class to save this data in your entire app

class SaveData{ 
   static int id 
   setId(int id1){
     id = id1;
  }
  getId(){
    return id;
   }
 }