After you build your flutter project you may want to reuse the models and business logic from your lib folder. I will show you how to go about setting up the project to have iOS, Android, Web, Windows, MacOS, Linux and a REST API interface with one project. The REST API can also be deploy to Google Cloud Run for Dart everywhere.

One Codebase for Client and Sever.

This will allow you to expose your Dart models as a REST API and run your business logic from your lib folder while the application runs the models as they are. Here is the final project.

Setting Up

As with any Flutter project I am going to assume that you already have Flutter installed on your machine and that you can create a project. This is a intermediate level difficulty so read on if you are up to the challenge. You will also need to know the basics of Docker.

Why one project?

It may not be obvious but when building complex applications you will at some point have a server and an application that calls that server. Firebase is an excellent option for doing this and I use it in almost all my projects. Firebase Functions are really powerful but you are limited by Javascript or Typescript. What if you could use the same packages that you are using in the Flutter project, or better yet what if they both used the same?

When you have a server project and a client project that communicate over a rest api or client sdk like Firebase then you will run into the problem that the server has models of objects stored and the client has models of the objects that are stored. This can lead to a serious mismatch when it changed without you knowing. GraphQL helps a lot with this since you define the model that you recieve. This approach allows your business logic to be always up to date for both the client and server.

Client Setup

The first step is to just build your application. The only difference that we will make is keeping the UI and business logic separate. When starting out with Flutter it can be very easy to throw all the logic into the screen and calling setState when the data changes. Even the application when creating a new Flutter project does this. That's why choosing a state management solution is so important.

To make things clean and concise we will make 2 folders in our lib folder.

ui for all Flutter Widgets and Screens

for all Flutter Widgets and Screens src for all business logic, classes, models and utility functions

This will leave us with main.dart being only the entry point into our client application.

import 'package:flutter/material.dart'; import 'plugins/desktop/desktop.dart';

import 'ui/home/screen.dart'; void main() {

runApp(MyApp());

}

@override

Widget build(BuildContext context) {

return MaterialApp(

title: 'Flutter Demo',

theme: ThemeData.light(),

darkTheme: ThemeData.dark(),

home: HomeScreen(),

);

}

} class MyApp extends StatelessWidget {Widget build(BuildContext context) {return MaterialApp(title: 'Flutter Demo',theme: ThemeData.light(),darkTheme: ThemeData.dark(),home: HomeScreen(),);

Let’s Start by making a tab bar for the 2 screens. Create a file in the folder ui/home/screen.dart and add the following:

import 'package:flutter/material.dart'; import '../counter/screen.dart';

import '../todo/screen.dart';

@override

_HomeScreenState createState() => _HomeScreenState();

} class HomeScreen extends StatefulWidget {_HomeScreenState createState() => _HomeScreenState(); class _HomeScreenState extends State<HomeScreen> {

int _currentIndex = 0; @override

Widget build(BuildContext context) {

return Scaffold(

body: IndexedStack(

index: _currentIndex,

children: <Widget>[

CounterScreen(),

TodosScreen(),

],

),

bottomNavigationBar: BottomNavigationBar(

currentIndex: _currentIndex,

onTap: (val) {

if (mounted)

setState(() {

_currentIndex = val;

});

},

type: BottomNavigationBarType.fixed,

items: [

BottomNavigationBarItem(

icon: Icon(Icons.add),

title: Text('Counter'),

),

BottomNavigationBarItem(

icon: Icon(Icons.list),

title: Text('Todos'),

),

],

),

);

}

} Widget build(BuildContext context) {return Scaffold(body: IndexedStack(index: _currentIndex,children: [CounterScreen(),TodosScreen(),],),bottomNavigationBar: BottomNavigationBar(currentIndex: _currentIndex,onTap: (val) {if (mounted)setState(() {_currentIndex = val;});},type: BottomNavigationBarType.fixed,items: [BottomNavigationBarItem(icon: Icon(Icons.add),title: Text('Counter'),),BottomNavigationBarItem(icon: Icon(Icons.list),title: Text('Todos'),),],),);

This is just a basic screen and should look very normal.

Counter Example

Now create a file ui/counter/screen.dart and add the following:

import 'package:flutter/material.dart';

import 'package:shared_dart/src/models/counter.dart';

@override

_CounterScreenState createState() => _CounterScreenState();

} class CounterScreen extends StatefulWidget {_CounterScreenState createState() => _CounterScreenState(); class _CounterScreenState extends State<CounterScreen> {

CounterModel _counterModel = CounterModel(); void _incrementCounter() {

setState(() {

// This call to setState tells the Flutter framework that something has

// changed in this State, which causes it to rerun the build method below

// so that the display can reflect the updated values. If we changed

// _counter without calling setState(), then the build method would not be

// called again, and so nothing would appear to happen.

_counterModel.add();

});

} @override

Widget build(BuildContext context) {

// This method is rerun every time setState is called, for instance as done

// by the _incrementCounter method above.

//

// The Flutter framework has been optimized to make rerunning build methods

// fast, so that you can just rebuild anything that needs updating rather

// than having to individually change instances of widgets.

return Scaffold(

appBar: AppBar(

// Here we take the value from the MyCounterPage object that was created by

// the App.build method, and use it to set our appbar title.

title: Text('Counter Screen'),

),

body: Center(

// Center is a layout widget. It takes a single child and positions it

// in the middle of the parent.

child: Column(

// Column is also a layout widget. It takes a list of children and

// arranges them vertically. By default, it sizes itself to fit its

// children horizontally, and tries to be as tall as its parent.

//

// Invoke "debug painting" (press "p" in the console, choose the

// "Toggle Debug Paint" action from the Flutter Inspector in Android

// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)

// to see the wireframe for each widget.

//

// Column has various properties to control how it sizes itself and

// how it positions its children. Here we use mainAxisAlignment to

// center the children vertically; the main axis here is the vertical

// axis because Columns are vertical (the cross axis would be

// horizontal).

mainAxisAlignment: MainAxisAlignment.center,

children: <Widget>[

Text(

'You have pushed the button this many times:',

),

Text(

'${_counterModel.count}',

style: Theme.of(context).textTheme.display1,

),

],

),

),

floatingActionButton: FloatingActionButton(

onPressed: _incrementCounter,

tooltip: 'Increment',

child: Icon(Icons.add),

), // This trailing comma makes auto-formatting nicer for build methods.

);

}

} Widget build(BuildContext context) {// This method is rerun every time setState is called, for instance as done// by the _incrementCounter method above.//// The Flutter framework has been optimized to make rerunning build methods// fast, so that you can just rebuild anything that needs updating rather// than having to individually change instances of widgets.return Scaffold(appBar: AppBar(// Here we take the value from the MyCounterPage object that was created by// the App.build method, and use it to set our appbar title.title: Text('Counter Screen'),),body: Center(// Center is a layout widget. It takes a single child and positions it// in the middle of the parent.child: Column(// Column is also a layout widget. It takes a list of children and// arranges them vertically. By default, it sizes itself to fit its// children horizontally, and tries to be as tall as its parent.//// Invoke "debug painting" (press "p" in the console, choose the// "Toggle Debug Paint" action from the Flutter Inspector in Android// Studio, or the "Toggle Debug Paint" command in Visual Studio Code)// to see the wireframe for each widget.//// Column has various properties to control how it sizes itself and// how it positions its children. Here we use mainAxisAlignment to// center the children vertically; the main axis here is the vertical// axis because Columns are vertical (the cross axis would be// horizontal).mainAxisAlignment: MainAxisAlignment.center,children: [Text('You have pushed the button this many times:',),Text('${_counterModel.count}',style: Theme.of(context).textTheme.display1,),],),),floatingActionButton: FloatingActionButton(onPressed: _incrementCounter,tooltip: 'Increment',child: Icon(Icons.add),), // This trailing comma makes auto-formatting nicer for build methods.);

This is the default counter app you get when you create a Flutter application but with one change, it uses `CounterModel` to hold the logic.

Create the counter model at src/models/counter.dart and add the following:

class CounterModel {

CounterModel(); int _count = 0; int get count => _count; void add() => _count++; void subtract() => _count--; void set(int val) => _count = val;

}

As you can see it is really easy to expose only what we want to while still having complete flexibility. You could use provider here if you choose, or even bloc and/or streams.

Todo Example

Lets create a file at ui/todos/screen.dart and add the following:

import 'package:flutter/material.dart'; import '../../src/classes/todo.dart';

import '../../src/models/todos.dart';

@override

_TodosScreenState createState() => _TodosScreenState();

} class TodosScreen extends StatefulWidget {_TodosScreenState createState() => _TodosScreenState(); class _TodosScreenState extends State<TodosScreen> {

final _model = TodosModel();

List<ToDo> _todos; @override

void initState() {

_model.getList().then((val) {

if (mounted)

setState(() {

_todos = val;

});

});

super.initState();

} void initState() {_model.getList().then((val) {if (mounted)setState(() {_todos = val;});});super.initState(); @override

Widget build(BuildContext context) {

return Scaffold(

appBar: AppBar(

title: Text('Todos Screen'),

),

body: Builder(

builder: (_) {

if (_todos != null) {

return ListView.builder(

itemCount: _todos.length,

itemBuilder: (context, index) {

final _item = _todos[index];

return ListTile(

title: Text(_item.title),

subtitle: Text(_item.completed ? 'Completed' : 'Pending'),

);

},

);

}

return Center(

child: CircularProgressIndicator(),

);

},

),

);

}

} Widget build(BuildContext context) {return Scaffold(appBar: AppBar(title: Text('Todos Screen'),),body: Builder(builder: (_) {if (_todos != null) {return ListView.builder(itemCount: _todos.length,itemBuilder: (context, index) {final _item = _todos[index];return ListTile(title: Text(_item.title),subtitle: Text(_item.completed ? 'Completed' : 'Pending'),);},);return Center(child: CircularProgressIndicator(),);},),);

You will see that we have the logic in TodosModel and uses the class ToDo for toJson and fromJson.

Create a file at the location src/classes/todo.dart and add the following:

// To parse this JSON data, do

//

// final toDo = toDoFromJson(jsonString); import 'dart:convert'; List<ToDo> toDoFromJson(String str) => List<ToDo>.from(json.decode(str).map((x) => ToDo.fromJson(x))); String toDoToJson(List<ToDo> data) => json.encode(List<dynamic>.from(data.map((x) => x.toJson()))); class ToDo {

int userId;

int id;

String title;

bool completed; ToDo({

this.userId,

this.id,

this.title,

this.completed,

}); factory ToDo.fromJson(Map<String, dynamic> json) => ToDo(

userId: json["userId"],

id: json["id"],

title: json["title"],

completed: json["completed"],

); Map<String, dynamic> toJson() => {

"userId": userId,

"id": id,

"title": title,

"completed": completed,

};

}

and create the model src/models/todo.dart and add the following:

import 'dart:convert'; import 'package:http/http.dart' as http;

import 'package:shared_dart/src/classes/todo.dart' as t;

final kTodosUrl = ' class TodosModel {final kTodosUrl = ' https://jsonplaceholder.typicode.com/todos' Future<List<t.ToDo>> getList() async {

final _response = await http.get(kTodosUrl);

if (_response != null) {

final _todos = t.toDoFromJson(_response.body);

if (_todos != null) {

return _todos;

}

}

return [];

} Future<t.ToDo> getItem(int id) async {

final _response = await http.get('$kTodosUrl/$id');

if (_response != null) {

final _todo = t.ToDo.fromJson(json.decode(_response.body));

if (_todo != null) {

return _todo;

}

}

return null;

}

}

Here we just get dummy data from a url that emits json and convert them to our classes. This is an example I want to show with networking. There is only one place that fetches the data.

Run the Project (Web)