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igorwojda
4.6K Stars 611 Forks MIT License 486 Commits 16 Opened issues

Description

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

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Android showcase

Kotlin Version AGP Gradle

codebeat badge CodeFactor

Showcase is a sample project that presents a modern, 2021 approach to Android application development.

The goal of the project is to combine popular libraries/tools and demonstrate best developement practices by utilizing up to date tech-stack and presenting 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.

Project characteristics and tech-stack

This project takes advantage of best practices, 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

Feature related code is placed inside one of the feature modules. We can think about each feature as the 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 life 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

Module types and module dependencies

This is a diagram present dependencies between project modules (Gradle sub-projects).

module_dependencies

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.

Feature module structure

Clean architecture
is the "core architecture" of the application, so each
feature module
contains own set of Clean architecture layers:

module_dependencies_layers

Notice that

app
module and
library_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.

feature_structure

Presentation layer

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)

Domain layer

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 - defies 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

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 the
domain
layer, not to perform any business logic (
domain
layer
use case
responsibility).
  • Mapper - maps
    data model
    to
    domain model
    (to keep
    domain
    layer independent from the
    data
    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.

Data flow

Below diagram presents application data flow when a user interacts with

album list screen
:

app_data_flow

Dependency management

This project utilizes multiple mechanics to easily share the same versions of dependencies.

App library dependencies

External dependencies (libraries) are defined using versions catalog feature in the settings.gradle file. These dynamic library versions are locked using Gradle docking dependency mechanism - concrete dependency versions are stored in

MODULE_NAME/gradle.lockfile
files.

To update lock files run

./gradlew test --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 plugin dependencies

Gradle plugins are defined in pluginManagement block (settings.gradle file).

Dynamic versions aren't supported for Gradle plugins, so docking 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.

Shared dependencies

Gradle is missing proper build-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 pipeline

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

PR Verification

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

Dependency updates

The update-dependencies task run periodically and creates a pull request containing dependency updates (updated gradle .lockfile files used by Gradle’s dependency locking).

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.

Upcoming improvements

Checklist of all upcoming enhancements.

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 an press
    Clone
    button

Command-line + Android Studio

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

Inspiration

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.

Cheat sheet

Android projects

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

Known issues

  • 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 eaisly shared between app libraries and Gradle plugins https://github.com/gradle/gradle/issues/16077

Contribute

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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 and are distributed under

Creative Commons License 2.0
: - Error screen by Chetan Potnuru - Building Screen by Carolina Cajazeira

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