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💎 Android application following best practices: Kotlin, Coroutines, JetPack, Clean Architecture, Feature Modules, Tests, MVVM, DI, Static Analysis...

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💎 Android Showcase 2.0

Kotlin Version AGP Gradle

Codebeat Badge CodeFactor

Android Showcase project presents a modern approach to Android application development and provides architectural guidance. This project utilizes popular tools, libraries, linters, Gradle plugins, testing frameworks, and CI setup. It is a complete sample of a fully functional Android application.

The project is focusing on modular, scalable, maintainable, and testable architecture, leading tech-stack, and demonstrating the best development practices.

This application may look simple, but it has all of the pieces that will provide the rock-solid foundation for the larger application suitable for bigger teams and extended application lifecycle.

Application Scope

The android-showcase displays information about music albums. The data is loaded from the Last.fm Music Discovery API.

The app has a few screens located in multiple feature modules:

  • Album list screen - displays list of albums
  • Album detail screen - display information about the selected album
  • Profile screen - empty (WiP)
  • Favourites screen - empty (WiP)

Tech-Stack

This project takes advantage of best practices, and many popular libraries and tools in the Android ecosystem. Most of the libraries are in the stable version unless there is a good reason to use non-stable dependency.

Architecture

By dividing a problem into smaller and easier-to-solve sub-problems, we can reduce the complexity of designing and maintaining a large system. Each module is an independent build block serving a clear purpose. We can think about each feature as a reusable component, the equivalent of microservice or private library.

The modularized code-base approach provides a few benefits:

  • reusability - enable code sharing and building multiple apps from the same foundation. Apps should be a sum of their features where the features are organized as separate modules.
  • separation of concerns - each module has a clear API. Feature-related classes live in different modules and can't be referenced without explicit module dependency. We strictly control what is exposed to other parts of your codebase.
  • features can be developed in parallel eg. by different teams
  • each feature can be developed in isolation, independently from other features
  • faster build time

Module Types And Module Dependencies

This diagram presents dependencies between project modules (Gradle sub-projects).

module_dependencies

We have three kinds of modules in the application:

  • app module - this is the main module. It contains code that wires multiple modules together (class, dependency injection setup, NavHostActivity, etc.) and fundamental application configuration (retrofit configuration, required permissions setup, custom Application class, etc.).
  • feature_x modules - the most common type of module containing all code related to a given feature. share some assets or code only between feature modules (currently app has no such modules)
  • feature_base modules that feature modules depend on to share a common code.

Feature Module Structure

Clean Architecture is implemented at the module level - each module contains its own set of Clean Architecture layers:

module_dependencies_layers

Notice that the app module and library_x modules structure differs a bit from the feature module structure.

Each feature module contains non-layer components and 3 layers with a distinct set of responsibilities.

feature_structure

Presentation Layer

This layer is closest to what the user sees on the screen.

The presentation layer mixes MVVM and MVI patterns:

  • MVVM - Jetpack ViewModel is used to encapsulate a common UI state. It exposes the state via observable state holder (Kotlin Flow)
  • MVI - action modifies the common UI state and emits a new state to a view via Kotlin Flow

The common state is a single source of truth for each view. This solution derives from Unidirectional Data Flow and Redux principles.

This approach facilitates the creation of consistent states. The state is collected via collectAsUiStateWithLifecycle method. Flows collection happens in a lifecycle-aware manner, so no resources are wasted.

Stated is annotated with Immutable annotation that is used by Jetpack compose to enable composition optimizations.

Components:

  • View (Fragment) - observes common view state (through Kotlin Flow). Compose transform state (emitted by Kotlin Flow) into application UI Consumes the state and transforms it into application UI (via Jetpack Compose). Pass user interactions to ViewModel. Views are hard to test, so they should be as simple as possible.
  • ViewModel - emits (through Kotlin Flow) view state changes to the view and deals with user interactions (these view models are not simply POJO classes).
  • ViewState - common state for a single view
  • StateTimeTravelDebugger - logs actions and view state transitions to facilitate debugging.
  • NavManager - singleton that facilitates handling all navigation events inside NavHostActivity (instead of separately, inside each view)

Domain Layer

This is the core layer of the application. Notice that the domain layer is independent of any other layers. This allows making domain models and business logic independent from other layers. In other words, changes in other layers will not affect the domain layer eg. changing the database (data layer) or screen UI (presentation layer) ideally will not result in any code change within the domain layer.

Components:

  • UseCase - contains business logic
  • DomainModel - defines the core structure of the data that will be used within the application. This is the source of truth for application data.
  • Repository interface - required to keep the domain layer independent from the data layer (Dependency inversion).

Data Layer

Encapsulates application data. Provides the data to the domain layer eg. retrieves data from the internet and cache the data in disk cache (when the device is offline).

Components:

  • Repository is exposing data to the domain layer. Depending on the application structure and quality of the external API repository can also merge, filter, and transform the data. These operations intend to create a high-quality data source for the domain layer. It is the responsibility of the Repository (one or more) to construct Domain models by reading from the Data Source and accepting Domain models to be written to the Data Source
  • Mapper - maps data model to domain model (to keep domain layer independent from the data layer).

This application has two Data Sources - Retrofit (used for network access) and Room (local storage used to access device persistent memory). These data sources can be treated as an implicit sub-layer. Each data source consists of multiple classes:

  • Retrofit Service - defines a set of API endpoints
  • Retrofit Response Model - definition of the network objects for given endpoint (top-level model for the data consists of ApiModels)
  • Retrofit Api Data Model - defines the network objects (sub-objects of the Response Model)
  • Room Database - persistence database to store app data
  • Room DAO - interact with the stored data
  • Room Entity - definition of the stored objects

Both Retrofit API Data Models and Room Entities contain annotations, so given framework understands how to parse the data into objects.

Data Flow

The below diagram presents application data flow when a user interacts with the album list screen:

app_data_flow

Dependency Management

Gradle versions catalog is used as a centralized dependency management third-party dependency coordinates (group, artifact, version) are shared across all modules (Gradle projects and subprojects).

All of the dependencies are stored in the settings.gradle.kts file (default location). Gradle versions catalog consists of a few major sections:

  • [versions] - declare versions that can be referenced by all dependencies
  • [libraries] - declare the aliases to library coordinates
  • [bundles] - declare dependency bundles (groups)
  • [plugins] - declare Gradle plugin dependencies

Each feature module depends on the feature_base module, so dependencies are shared without the need to add them explicitly in each feature module.

The project enables the TYPESAFE_PROJECT_ACCESSORS experimental Gradle feature to generate type-safe accessors to refer other projects.

// Before
implementation(project(":feature_album"))

// After
implementation(projects.featureAlbum)

Logcat debugging

To facilitate debuting project contains logs. You can filter logs to understand app flow. Keywords:

  • onCreate see what Activities and Fragments have been created
  • Action - filter all actions performed on the screens to update the UI
  • Http - debug network requests and responses

CI Pipeline

CI is utilizing GitHub Actions. The complete GitHub Actions config is located in the .github/workflows folder.

Pull Request Verification

Series of workflows run (in parallel) for every opened PR and after merging PR to the main branch:

  • ./gradlew lintDebug - checks that source code satisfies Android lint rules
  • ./gradlew detektCheck - checks that sourcecode satisfies detekt rules
  • ./gradlew detektApply - applies detekt code formatting rules to sourcecode in-place
  • ./gradlew spotlessCheck - checks that source code satisfies formatting steps.
  • ./gradlew spotlessApply - applies code formatting steps to source code in-place.
  • ./gradlew testDebugUnitTest - run unit tests
  • ./gradlew connectedCheck - run UI tests
  • ./gradlew :app:bundleDebug - create application bundle

Design Decisions

Read related articles to have a better understanding of underlying design decisions and various trade-offs.

What This Project Does Not Cover?

The interface of the app utilizes some of the modern material design components, however, is deliberately kept simple to focus on application architecture and project config.

Getting Started

There are a few ways to open this project.

Android Studio

  1. Android Studio -> File -> New -> From Version control -> Git
  2. Enter https://github.com/igorwojda/android-showcase.git into URL field and press Clone button

Command-line And Android Studio

  1. Run git clone https://github.com/igorwojda/android-showcase.git command to clone the project
  2. Open Android Studio and select File | Open... from the menu. Select the cloned directory and press Open button

Plugins

It is recommended installing Detekt to Android Studio. To configure the plugin open Android Studio preferences, open Tools, open Detekt and add detekt.yml configuration file.

Upcoming Improvements

This project is under active development and it is being occasionally refined.

Check the list of all upcoming enhancements.

Inspiration

Here are few additional resources.

Cheatsheet

Android Projects

Other high-quality projects will help you to find solutions that work for your project (random order):

Other

Known Issues

  • No usages are found for the suspended Kotlin invoke operator (KTIJ-1053)
  • The Material You Dynamic Colors are not correctly applied to Fragment contents (only to Activity)
  • When using FragmentContainerView, NavController fragment can't be retrieved by using findNavController() (ISSUE-142847973, STACKOVERFLOW-59275182)
  • Mockk is unable to mock some methods with implicit continuation parameter in the AlbumListViewModelTest class (Issue-957)
  • Jetpack compose compiler depends on specific Kotlin version. Kotlin upgrade is blocked until compose catches up (error: This version (x.x.x) of the Compose Compiler requires Kotlin version x.x.x but you appear to be using Kotlin version y.y.y which is not known to be compatible) (disabled in Renovate)
  • KSP depends on specific Kotlin version so, dependencies must be upgraded together (disabled in Renovate).
  • Mockk can;t find an answer for suspended function, so test in the AlbumDetailViewModelTest was disabled
  • Dynamic feature module is not supported by ANDROID_TEST_USES_UNIFIED_TEST_PLATFORM yet.
  • ktlint FileName rule has to be disabled, because it is not compatible with fie contain a single extension ISSUE-1657
  • Delegate import is not provided when a variable has the same name as Delegate (KTIJ-17403)
  • androidx.compose.runtime.getValue and androidx.compose.runtime.setValue imports are can't be resolved automatically - they had to be added manually KTIJ-23200
  • Gradle Versions Catalog code is marked as an error in build.gradle.kts files (KTIJ-19370, KTIJ-19585)
  • ktlint import-ordering rule conflicts with IDE default formatting rule, so it have to be .editorconfig file. and KTIJ-16847)
  • False positive "Unused symbol" for a custom Android application class referenced in AndroidManifest.xml file (KT-27971)
  • Android lint complains about exceeding access rights to ArchTaskExecutor (Issue 79189568)
  • JUnit 5 does not support tests with suspended modifier (Issue 1914)
  • Custom detekt config is hard to update (Issue 4517)
  • Coil does not provide a way to automatically retry image load, so some images may not be loaded when connection speed is low (Issue 132)

Contribute

This project is being maintained to stay up to date with leading industry standards. Please check the CONTRIBUTING page if you want to help.

Author

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License

MIT License

Copyright (c) 2019 Igor Wojda

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
associated documentation files (the "Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial
portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF  TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Animations License

Flowing animations are distributed under Creative Commons License 2.0:

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💎 Android application following best practices: Kotlin, Coroutines, JetPack, Clean Architecture, Feature Modules, Tests, MVVM, DI, Static Analysis...

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