astronomy_picture_of_the_day

Contents

• Overview
• Getting Started
• Running the App
• Main Application Features
• Project Structure Overview
  • Project Architecture
  • Directory Structure
  • Package by feature
• Core Third-Party Packages
• References

Overview

This is a Flutter app project to display NASA's astronomy picture of the day.

Getting Started

This project is a fully functional example, focussed on showing astronomy-related images by making http requests to NASA's public APIs.

You can take the code in this project and experiment with it.

  git clone https://github.com/dartoos-dev/astronomy_picture_of_the_day.git
  cd astronomy_picrture_of_the_day

Running the App

As it is a Flutter project, you can run it on different platforms — Android, IoS, Web, etc. But before running the application, you need to know which devices are connected to your computer; you can achieve this by listing all devices with the following terminal command:

  flutter devices

The above command will display a list similar to:

For example, to run the app on one of the listed devices in debug mode:

Android

  flutter run -d RQCW70

IoS

  flutter run -d 257E76

Chrome

  flutter run -d chrome

Main Application Features

• List of astronomy pictures of the day retrieved from NASA's public API.
• Detail page of selected picture.
• Pull-to-refresh capability.
• Pagination.
• Automatically retries http requests when the device connection is intermittent or the server is offline at the time of the request — it uses an exponential backoff algorithm to retry the failed requests.
• It still works when offline.

Project Structure Overview

Project Architecture

• Clean Architecture

Directory Structure

lib  
└───features  
│   └───feature1  
│   │  	└───sub_feature  
│   │   └───data  
│   │   └───domain  
│   │   └───external  
│   │   └───presenter  
│   └───feature2  
│   │  	└───sub_feature  
│   │  	└───data  
│   │  	└───domain  
│   │  	└───external  
│   │  	└───presenter  
└───shared  
│   app_module.dart  
│   app_widget.dart 
│   main.dart 

Package by feature

In regard to packages or modules, this project uses the "package-by-feature" approach rather than the more usual "package-by-layer". The former uses packages to reflect the feature set; it places all items related to a single feature into a single directory whose name corresponds to important, high-level aspects of the problem domain.

It is important to note that package-by-feature style still honors the idea of separating layers, but that separation is implemented using separate classes.

Advantages of package by feature

• easy and logical code navigation — all items needed for a task are usually in the same directory.
• emphasis on core services rather than implementation details.
• scope minimization (package-private as default, not public as in package-by-layer).
• low coupling between modules.
• scalability: the number of classes remains limited to the items related to a specific feature.

Drawbacks of package by layer

• poor overview of all classes that belong to a feature.
• complex, hard to understand, and easy to break code as impact of a change is hard to grasp.
• leads to central classes containing all methods for every use case. Over time, those methods get bigger (with extra parameters) to fulfill more use cases.

Core Third-Party Packages

• dartz: functional library.
• dio: http client library.
• flutter_modular: dependency injection and routing.
• lint: stricter static analysis rules.
• localization: simplifies in-app translation.
• mocktail: mock framework for unit testing purposes.

References

• API NASA
• Clean Dart
• package by feature
• package by feature, not layer