Scalable app structure in flutter

I was recently exploring flutter and built a very minimal app in a day to try out the framework. I built a minimal app which takes take few inputs from user, add validations, number formatting and show an alert box when user presses submit.

I was amazed by framework itself so I decided to give a try for a medium size application in which we should be able to do following:-

1. Login/Register in a user. This may be done via Google or Facebook.
2. Once the user is logged in registered show him(or her) the dashboard and other details.
3. If user wants to place he can do by adding items to a cart and then proceeding to payment.

This is basically a mini version of an e-commerce application.

Now, before finalising a folder structure we need to understand a simple thing about scalability; a scalable structure should be so modular that even if that module is removed or changed the application should not break.

I decided to use the similar project structure which I was using for my react-native applications.

So lets get started.

Here is the core folder structure which flutter provides.

flutter-app/
|- android
|- build
|- ios
|- lib
|- test

Now, lets dive into the lib folder which has the main code for the application.

1. screens — Contains the screens of your application. All files from here get imported into routes.dart
2. util — Contains the utilities/common functions of your application
3. widgets — Contains the common widgets for your applications. For example, Button , TextField etc.
4. routes.dart — Contains the routes of your application and imports all screens.

lib/
|- main.dart
|- routes.dart
|- screens/
|- util/
|- widgets/
|- data/
|- services/

SCREENS-

screens/
|- auth
   |- auth.dart
   |- index.dart
   |- widgets
      |- googleButton
        |- google_button.dart
        |- google_button_container.dart
        |- index.dart
      |- facebookButton
        |- facebook_button.dart
        |- facebook_button_container.dart
        |- index.dart

This screen contains 2 buttons giving user an option to login from Google or Facebook .

So, now we know that these 2 buttons are not going to get used anywhere else in the application so we nest them inside this screen.

Widgets which would be used only inside a particular screen should be placed inside that screen and not inside the common widgets folder.

If you see this nesting really helps in case I wanted to following later on in my code:-

1. If I wanted to modify something in these buttons I can directly come inside this folder else I have to search for them in common folders if I place them there.
2. Removing this module is really easy as we know no other part of code is impacted by this.

Now, if we go a bit further we see that the button being used in googleButton and facebookButton is common and is being used from widgets folder with only styles being overrided. This makes the button size uniform across the entire application.

widgets/
|- button.dart // Common button

UTIL-

util
|- date_utils.dart
|- format_utils.dart

Util folder contains the business logic of your application. For example, if you are working on an e-commerce application few of them could be:-

1. Calculating total amount in cart.
2. Showing dates, currency etc. in proper format.

WIDGETS-

As I mentioned above widgets would contain the common used across the application.

We follow the same nesting pattern here as we did for screens. The widgets required only by a single widget should be nested inside that widget and should be only accessible to immediate parent.

widgets/
|- app_button/
  |- app_button.dart
  |- index.dart

DATA-

This folder would come into the picture once you integrate redux(or other) store into the application. Here you would put your reducers, actions etc.

data/
|- auth
   |- access_token
      |- actions.dart
      |- reducer.dart
   |- refresh_token
      |- actions.dart
      |- reducer.dart
   |- reducer.dart

SERVICES-

This would handle all network and business logic of your application. For example, once you are authenticated with facebook/google you need to update backend with access tokens you can place that authentication in this folder.

services/
|- authentication.dart

Well, that is how I structure my mobile applications with flutter.

I would love to here how you guys do it.

I have also created a repository where you can see the actual structure.