Android Best Practices

Agenda

● Introduction

● The clean architecture

● Testing

● Support library

● Libraries we can depend on

● What's next

Introduction

Android StudioGradle

Material DesignLollipop

AndroidWear / Auto / TV

Introduction

The clean architecture

The clean architecture

The key concept is based on:

● Independence of frameworks

● Testeable

● Independent of UI

● Independent of DB

● Independent of any external agency

The clean architecture

Definitions

● Entities: These are the business objects of

the application

● Use Cases: These use cases orchestrate the

flow of data to and from the entities.

● Interface Adapters: This set of adapters

convert data from the format most

convenient for the use cases and entities.

● Frameworks and Drivers: This is where all

the details go: UI, tools, frameworks, etc.

Android architecture

The objective is the separation of concerns by keeping the business rules not knowing anything at all about the

outside world, thus, they can can be tested without any dependency to any external element.

To achieve this, the proposal is about breaking up the project into 3 different layers, in which each one has its own

purpose and works separately from the others.

Presentation layer

Is here, where the logic related with views and animations happens. It uses no more than a Model View Presenter (MVP), but you can use any other pattern like MVC or MVVM.

For example, fragments and activities are only views, there is no logic inside them other than UI logic, and this is where all the rendering stuff takes place.

Presenters in this layer are composed with interactors (use cases) that perform the job in a new thread outside the android UI thread, and come back using a callback with the data that will be rendered in the view.

Domain layer

Business rules here: all the logic happens in this layer. Regarding the

android project, you will see all the interactors (use cases)

implementations here as well.

This layer is a pure java module without any android dependencies. All

the external components use interfaces when connecting to the

business objects.

Data layer

All data needed for the application comes from this layer through a Repository implementation (the interface is in the

domain layer) that uses a Repository Pattern with a strategy that, through a factory, picks different data sources

depending on certain conditions.

The idea behind all this is that the data origin

is transparent for the client, which does not

care if the data is coming from memory, disk

or the cloud, the only truth is that the data

will arrive and will be got.

Project structure

Presentation module

Is the Android application itself, with its resources,

assets, logic, etc.

Project structure

Domain module

This module hosts use-cases and their implementations,

it is the business logic of the application.

Project structure

Model module

This module is responsible for managing the

information, select, save, delete, etc.

Communication

Now, how we communicate these layers?

One approach is communication over an Message Bus system. This system is very useful for Broadcast events, or to establish a communication between components.

Basically, events are sent through a Bus and the classes interested to consume that event have to subscribe to that Bus.

To implement the system bus, we used the library Otto by Square, but we can use EventBus by GreenRobot too. Both libraries implements the publish/subscribe pattern.

Communication

Testing

Testing

We have different solutions for each layer:

● Presentation Layer: Android instrumentation and Espresso for integration and functional testing

● Domain Layer: JUnit plus Mockito for unit tests

● Data Layer: Robolectric (since this layer has android dependencies) plus JUnit plus Mockito for integration and unit tests.

Espresso

Espresso is a testing framework that exposes a simple API to perform UI testing of Android apps. With the latest 2.0 release, Espresso is now part of the Android Support Repository which makes it more easier to add automated testing support for your project.

Key features:

● Its code looks a lot like English, which makes it predictable and easy to learn.

● The API is relatively small, and yet open for customization.

● Espresso tests run optimally fast (no waits, sleeps)

● Gradle + Android Studio support

Espresso

Is built up from 3 major components:

These components are:

● ViewMatchers – allows you to locate a view in the current view hierarchy● ViewActions – allows you to interact with views● ViewAssertions – allows you to assert the state of a view.

For simplicity, you may use these shortcuts to refer to them:

● ViewMatchers – “find something“● ViewActions – “do something“● ViewAssertions – “check something“

Espresso

Here is an example for this:

Espresso

Here is an example for this:

JUnit

JUnit in version 4.x is a test framework which uses annotations to identify methods that specify a test.

JUnit

From Android Studio 1.1, we have fully integration with JUnit.

Support Library

Support Library

Design Support Library

This library implements some custom views from Material Design such as:

NEW

Support Library

Design Support Library

Support Library

V7 Appcompat Library - IMPORTANT!!!

This library adds support from API V7 (Android 2.1) for basic

elements:

● Toolbar

● CardView

● GridLayout

● PaletteLibrary

● RecyclerView

● … and more

Support Library

V4 Support Library

This library adds support from API V4 (Android 1.6) for basic

elements:

● Fragment

● NotificationCompat

● ViewPager

● PagerTitle

● DrawerLayout

● ... and a lot more

Support Library

Testing Support Library

This library provides an extensive framework for testing Android apps. You can run tests created

using these APIs from the Android Studio IDE or from the command line.

Includes the following test automation tools:

● AndroidJUnitRunner: JUnit 4-compatible test runner for Android

● Espresso: UI testing framework; suitable for functional UI testing within an app

● UI Automator: UI testing framework; suitable for cross-app functional UI testing across

system and installed apps

Libraries we can depend on

Why libraries?

● Maintained by the community

● Easy to use

● Well documented

● It just works!!!

● Don't reinvent the wheel!!!

Retrofit

Type-safe REST client for Android and Java by Square, Inc.

Retrofit turns your REST API into a Java interface.

The RestAdapter class generates an implementation of the GitHubService interface.

Retrofit

Each call on the generated GitHubService makes an HTTP request to the remote webserver.

More examples:

Picasso

Image transformation

Picasso allows for hassle-free image loading in your application — often in one line of code!

ButterKnife

View injection library

Annotate fields with @InjectView and a view ID for Butter Knife to find and automatically cast the corresponding view in your layout.

Gson

Gson is a Java library that can be used to convert Java Objects into their JSON representation. It

can also be used to convert a JSON string to an equivalent Java object.

Gson

We can customize named fields, this improves code readability:

Stetho

Stetho is a sophisticated debug bridge for

Android applications.

When enabled, developers have access to

the Chrome Developer Tools feature

natively part of the Chrome desktop

browser.

How?

Adding this libraries to our project it's really easy.

This libraries are located in two main repositories:

● Maven Central● JCenter - Default on Android Studio

On our build.gradle file, we add:

Finding libraries

Android Arsenal Gradle, please

What’s next?

Finding libraries

● RXJava - Reactive Programming

● Dagger2 - Dependency Injection

● Kotlin - New scripting language

References

● Robert Martin - The Clean Architecture

● Fernando Cejas - The Clean Architecture

● Gradle - Android Tools

● Android Developers - Support Libraries

● Design Support Library Examples - Repository

● Retrofit - REST Adapter

● Picasso - Image loader

● Gson - JSON parser

● Stetho - View inspector

● Espresso - Samples

● Android Arsenal - For libraries / Gradle Please - Gradle dependencies

Thanks