Android Showcase

💎 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

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The Android Showcase project exemplifies modern Android application development methodologies and provides comprehensive architectural guidance. By integrating popular development tools, libraries, linters, and Gradle plugins, along with robust testing frameworks and Continuous Integration (CI) setup, this project offers a holistic sample of a fully operational Android application.

The primary focus of this project lies in promoting a modular, scalable, maintainable, and testable architecture. It incorporates a leading-edge tech-stack and embodies the finest practices in software development. While the application may appear straightforward, it encompasses all the crucial components that lay the groundwork for a robust, large-scale application.

The design principles and architectural choices applied in this project are ideally suited for larger teams and extended application lifecycles. This application is not just about showcasing functionalities, but it is also a testament to how well-structured and well-written code serves as a stable backbone for scalable and maintainable software development projects.

Application Scope

The android-showcase is a simple application that presents information about various music albums. This data is dynamically sourced from the music platform 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)


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.


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).


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:


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.


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.


  • 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.


  • 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).


  • 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 a 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 the 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:


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

// After

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 the source code in place.
  • ./gradlew testDebugUnitTest - run unit tests
  • ./gradlew connectedCheck - run UI tests
  • ./gradlew :app:bundleDebug - create an 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 into URL field and press Clone button

Command-line And Android Studio

  1. Run git clone command to clone the project
  2. Open Android Studio and select File | Open... from the menu. Select the cloned directory and press Open button


It is recommended to install 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.


Here are a few additional resources.


Android Projects

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


Known Issues

  • In Gradle 8.1 the version catalog type safe API is not available for buildSrc directory, so dependencies and versions have to be retrieved using type unsafe API:
    • plugins are retrieved using string plugin ids
    • versions (kotlinCompilerExtensionVersion) are retrieved using string version names
  • 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), , so test in the AlbumDetailViewModelTest was disabled
  • Automatic Kotlin upgrade is disabled in Renovate, because these dependencies have to be updated together with Kotlin: until:
  • 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
  • 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)
  • buildFeatures and testOptions blocks are incubating and have to be marked as @Suppress ("UnstableApiUsage")


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


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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.


Animations License

Flowing animations are distributed under Creative Commons License 2.0:

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