Showcase is a sample project that presents a modern approach to Android application development.
The goal of the project is to combine popular libraries/tools and demonstrate best development practices by utilizing an up-to-date tech-stack and presenting a modern Android application Architecture that is modular, scalable, maintainable, and testable. This application may look simple, but it has all the pieces that will provide the rock-solid foundation for the larger app suitable for bigger teams and long application lifecycle.
This project is being maintained to match industry standards. Please check CONTRIBUTING page if you want to help.
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.
- Tech-stack
- 100% Kotlin + Coroutines - perform background operations
- Retrofit - networking
- Jetpack
- Navigation - in-app navigation
- LiveData - notify views about database change
- Lifecycle - perform an action when lifecycle state changes
- ViewModel - store and manage UI-related data in a lifecycle conscious way
- Room - store offline cache
- Kodein - dependency injection
- Coil - image loading library
- Lottie - animation library
- Stetho - application debugging
- Modern Architecture
- Clean Architecture (at feature module level)
- Single activity architecture using Navigation component
- MVVM + MVI (presentation layer)
- Dynamic feature modules
- Android Architecture components (ViewModel, LiveData, Navigation)
- Android KTX - Jetpack Kotlin extensions
- CI
- GitHub Actions
- Automatic PR verification including tests, linters and 3rd online tools
- Testing
- Unit Tests (JUnit 5 via android-junit5)
- UT Tests (Espresso)
- Mockk - mocking framework
- Kluent - assertion framework
- UI
- Material design
- Reactive UI
- Static analysis tools
- Gradle
- Gradle Kotlin DSL
- Custom tasks
- Plugins (SafeArgs, android-junit5)
- Dependency locks
- Versions catalog
Feature related code is placed inside one of the feature modules. We can think about each feature as the reusable component, equivalent of microservice or private library.
The modularized code-base approach provides few benefits:
- better 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.
- features can be developed in parallel eg. by different teams
- each feature can be developed in isolation, independently from other features
- faster compile time
This diagram presents dependencies between project modules (Gradle sub-projects).
Note that due usage of Android dynamic-feature
module dependencies are reversed (feature modules are depending on app
module, not another way around).
We have three kinds of modules in the application:
app
module - this is the main module. It contains code that wires multiple modules together (dependency injection setup,NavHostActivity
, etc.) and fundamental application configuration (retrofit configuration, required permissions setup, custom application class, etc.).- application-specific
library_x
modules that some of the features could depend on. This is helpful if you want to share some assets or code only between few feature modules (currently app has no such modules) - feature modules - the most common type of module containing all code related to a given feature.
Clean architecture
is the "core architecture" of the application, so each feature module
contains own set of Clean architecture layers:
Notice that
app
module andlibrary_x
modules structure differs a bit from feature module structure.
Each feature module contains non-layer components and 3 layers with distinct set of responsibilities.
This layer is closest to what the user sees on the screen. The presentation
layer is a mix of MVVM
(Jetpack ViewModel
used to preserve data across activity restart) and
MVI
(actions
modify the common state
of the view and then new state is edited to a view via LiveData
to be rendered).
common state
(for each view) approach derives from Unidirectional Data Flow and Redux principles.
Components:
- View (Fragment) - presents data on the screen and pass user interactions to View Model. Views are hard to test, so they should be as simple as possible.
- ViewModel - dispatches (through
LiveData
) 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
- NavManager - singleton that facilitates handling all navigation events inside
NavHostActivity
(instead of separately, inside each view)
This is the core layer of the application. Notice that the domain
layer is independent of any other layers. This allows to make domain models and business logic independent from other layers.
In other words, changes in other layers will have no effect on domain
layer eg. changing database (data
layer) or screen UI (presentation
layer) ideally will not result in any code change withing 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 thedata layer
(Dependency inversion).
Manages application data and exposes these data sources as repositories to the domain
layer. Typical responsibilities of this layer would be to retrieve data from the internet and optionally cache this data locally.
Components:
-
Repository is exposing data to the
domain
layer. Depending on application structure and quality of the external APIs repository can also merge, filter, and transform the data. The intention of these operations is to create high-quality data source for thedomain
layer, not to perform any business logic (domain
layeruse case
responsibility). -
Mapper - maps
data model
todomain model
(to keepdomain
layer independent from thedata
layer). -
RetrofitService - defines a set of API endpoints.
-
DataModel - defines the structure of the data retrieved from the network and contains annotations, so Retrofit (Moshi) understands how to parse this network data (XML, JSON, Binary...) this data into objects.
Below diagram presents application data flow when a user interacts with album list screen
:
This project utilizes multiple mechanics to easily share the same versions of dependencies.
External dependencies (libraries) are defined using versions catalog feature in the settings.gradle file. These dynamic library versions are locked using Gradle locking dependency mechanism - concrete dependency versions are stored in MODULE_NAME/gradle.lockfile
files.
To update lock files run ./gradlew test lint s --write-locks
command and commit updated gradle.lockfile
files to
repository.
Each feature module depends on the app
module, so dependencies are shared without need to add them explicitly in each feature module.
Gradle plugins are defined in pluginManagement block (settings.gradle file).
Dynamic versions aren't supported for Gradle plugins, so locking dependency mechanism can't be used (like for app library dependencies), and thus versions of some libraries & plugins have to be hardcoded in the gradle.properties file.
There is no easy way to share id between pluginManagement
block and buildSrc
folder, so plugin ids (also used within build scripts), have to be duplicated in the GradlePluginId file.
Gradle is missing proper built-in mechanism to share dependency versions between app library dependency and Gradle plugin dependency eg. Navigation component library uses Safe Args Gradle plugin with the same version.
To enable sharing all versions that are used for both plugins and libraries are defined in gradle.properties.
Unfortunately this technique cannot be applied to older Gradle plugins (added by classpath
, not by pluginManagement
), so some version in the gradle.properties are still duplicated.
CI is utilizing GitHub Actions. Complete GitHub Actions config is located in the .github/workflows folder.
Series of workflows runs (in parallel) for every opened PR and after merging PR to main
branch:
./gradlew lintDebug
- runs Android lint./gradlew detekt
- runs detekt./gradlew ktlintCheck
- runs ktlint./gradlew testDebugUnitTest
- run unit tests./gradlew connectedCheck
- run UI tests./gradlew :app:bundleDebug
- create app bundle
The update-dependencies task run periodically and creates a pull request containing dependency updates (updated gradle .lockfile files used by Gradle’s dependency locking).
Read related articles to have a better understanding of underlying design decisions and various trade-offs.
- Multiple ways of defining Clean Architecture layers
- More coming soon
./gradlew wrapper --gradle-version=1.2.3
The interface of the app utilizes some of the modern material design components, however, is deliberately kept simple to focus on application architecture.
Checklist of all upcoming enhancements.
There are a few ways to open this project.
Android Studio
->File
->New
->From Version control
->Git
- Enter
https://github.com/igorwojda/android-showcase.git
into URL field an pressClone
button
- Run
git clone https://github.com/igorwojda/android-showcase.git
command to clone project - Open
Android Studio
and selectFile | Open...
from the menu. Select cloned directory and pressOpen
button
This is project is a sample, to inspire you and should handle most of the common cases, but please take a look at additional resources.
- Core App Quality Checklist - learn about building the high-quality app
- Android Ecosystem Cheat Sheet - board containing 200+ most important tools
- Kotlin Coroutines - Use Cases on Android - most popular coroutine usages
Other high-quality projects will help you to find solutions that work for your project:
- Iosched - official Android application from google IO 2019
- Android Architecture Blueprints v2 - a showcase of various Android architecture approaches
- Android sunflower complete
Jetpack
sample covering all libraries - GithubBrowserSample - multiple small projects demonstrating usage of Android Architecture Components
- Plaid - a showcase of Android material design
- Clean Architecture boilerplate - contains nice diagrams of Clean Architecture layers
- Android samples - official Android samples repository
- Roxie - solid example of
common state
approach together witch very good documentation - Kotlin Android template - template that lets you create an Android/Kotlin project and be up and running in a few seconds.
- Gradle 7.1.1 is not compatible with GradleJDK 16 (build is failing, so JDK 15 must be used)
ktlint
import-ordering
rule conflicts with IDE default formatting rule, so it have to be disabled. This is partially fixed in AS 4.2 (see Issue 527 and Issue KT-10974)- False positive "Unused symbol" for a custom Android application class referenced in AndroidManifest.xml file (Issue 27971)
- False positive "Function can be private" (Issue KT-33610)
- False positive cannot access class (Issue 16077). This is fixed in InteliJ IDEA 2021.1 EAP 1 afair.
- Gradle has no way to share dependency versions between library and Gradle plugin or prod and test version of the library (Issue 16077)
- Android lint complains about exceeding access rights to ArchTaskExecutor Issue 79189568
- JUnit 5 does not support tests with suspended modifier (Issue 1914)
- Gradle dependencies can't be easily shared between app libraries and Gradle plugins gradle/gradle#16077
Want to contribute? Check our Contributing docs.
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.
Flowing animations and are distributed under Creative Commons License 2.0
:
- Error screen by Chetan Potnuru
- Building Screen by Carolina Cajazeira