Gradle for Android

Table of Contents

Gradle for Android

Credits

About the Author

About the Reviewers

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Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Errata

Piracy

Questions

1. Getting Started with Gradle and Android Studio

Android Studio

Staying up to date

Understanding Gradle basics

Projects and tasks

The build lifecycle

The build configuration file

The project structure

Creating a new project

Getting started with the Gradle Wrapper

Getting the Gradle Wrapper

Running basic build tasks

Migrating from Eclipse

Using the import wizard

Migrating manually

Keeping the old project structure

Converting to the new project structure

Migrating libraries

Summary

2. Basic Build Customization

Understanding the Gradle files

The settings file

The top-level build file

The module build file

Plugin

Android

Dependencies

Getting started with tasks

Base tasks

Android tasks

Inside Android Studio

Customizing the build

Manipulating manifest entries

Inside Android Studio

BuildConfig and resources

Project-wide settings

Project properties

Default tasks

Summary

3. Managing Dependencies

Repositories

Preconfigured repositories

Remote repositories

Local repositories

Local dependencies

File dependencies

Native libraries

Library projects

Creating and using library project modules

Using .aar files

Dependency concepts

Configurations

Semantic versioning

Dynamic versions

Inside Android Studio

Summary

4. Creating Build Variants

Build types

Creating build types

Source sets

Dependencies

Product flavors

Creating product flavors

Source sets

Multiflavor variants

Build variants

Tasks

Source sets

Resource and manifest merging

Creating build variants

Variant filters

Signing configurations

Summary

5. Managing Multimodule Builds

The anatomy of a multimodule build

The build lifecycle revisited

Module tasks

Adding modules to a project

Adding a Java library

Adding an Android library

Integrating Android Wear

Using Google App Engine

Analyzing the build file

Using the backend in an app

Custom tasks

Tips and best practices

Running module tasks from Android Studio

Speeding up multimodule builds

Module coupling

Summary

6. Running Tests

Unit tests

JUnit

Robolectric

Functional tests

Espresso

Test coverage

Jacoco

Summary

7. Creating Tasks and Plugins

Understanding Groovy

Introduction

Classes and members

Methods

Closures

Collections

Groovy in Gradle

Getting started with tasks

Defining tasks

Anatomy of a task

Using a task to simplify the release process

Hooking into the Android plugin

Automatically renaming APKs

Dynamically creating new tasks

Creating your own plugins

Creating a simple plugin

Distributing plugins

Using a custom plugin

Summary

8. Setting Up Continuous Integration

Jenkins

Setting up Jenkins

Configuring the build

TeamCity

Setting up TeamCity

Configuring the build

Travis CI

Configuring the build

Further automation

The SDK manager plugin

Running tests

Continuous deployment

Beta distribution

Summary

9. Advanced Build Customization

Reducing the APK file size

ProGuard

Shrinking resources

Automatic shrinking

Manual shrinking

Speeding up builds

Gradle properties

Android Studio

Profiling

Jack and Jill

Ignoring Lint

Using Ant from Gradle

Running Ant tasks from Gradle

Importing an entire Ant script

Properties

Advanced app deployment

Split APK

Summary

Index

Gradle for Android

Gradle for Android

Copyright © 2015 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: July 2015

Production reference: 1140715

Published by Packt Publishing Ltd.

Livery Place

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Birmingham B3 2PB, UK.

ISBN 978-1-78398-682-8

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Credits

Author

Kevin Pelgrims

Reviewers

Peter Friese

Jonathan H. Kau

Takuya Miyamoto

Marco A. Rodriguez-Suarez

Felix Schulze

Hugo Visser

Commissioning Editor

Amarabha Banerjee

Acquisition Editor

Nikhil Karkal

Content Development Editor

Prachi Bisht

Technical Editor

Pankaj Kadam

Copy Editors

Puja Lalwani

Laxmi Subramanian

Project Coordinator

Shipra Chawhan

Proofreader

Safis Editing

Indexer

Tejal Soni

Production Coordinator

Manu Joseph

Cover Work

Manu Joseph

About the Author

Kevin Pelgrims started his career as a .NET developer in Belgium. After some years working on Windows and web development for corporate clients, he moved to Copenhagen to become part of its start-up community. There, he began working on mobile platforms, and within a year, he was the lead developer of several Android and Windows Phone apps. Kevin is also a regular speaker at the Android developers group in Copenhagen. He maintains multiple Android apps in his spare time and likes to experiment with server-side technology. When he is not busy writing code, he is most likely playing the guitar with his wife and their cat.

To follow what Kevin is up to, you can take a look at his blog at http://www.kevinpelgrims.com or follow him on Twitter at @kevinpelgrims.

I could not have written this book without the support of my brilliant wife, Louise. Not only did she put up with me spending entire evenings and weekends with my computer, she also proofread the entire book, improving the language and the grammar.

I would like to thank Packt Publishing for giving me the opportunity to write this book, especially Nikhil Karkal and Prachi Bisht, for believing in me and guiding me throughout the process. I appreciate the help of my friend Koen Metsu, whose comments helped in making sure that the explanations and examples are easy to understand. Thanks to Anders Bo Pedersen and Emanuele Zattin for coming up with several improvements.

I also want to thank the reviewers: Hugo Visser, Peter Friese, Felix Schulze, Takuya Miyamoto, Jonathan H. Kau, and Marco Rodriguez-Suarez. Their input has significantly improved the content of this book. Last but not least, special thanks to our cat, Jigsaw, who encouraged me to stay focused and keep going, by sitting on my lap so I couldn't get up.

About the Reviewers

Peter Friese works as a developer advocate at Google in the Developer Relations team in London, UK. He is a regular open source contributor, blogger, and public speaker. He is on Twitter at @peterfriese and on Google+ at +PeterFriese. You can find his blog at http://www.peterfriese.de.

Jonathan H. Kau is an experienced Android developer, having published several standalone applications to Google Play and worked on numerous hackathon projects leveraging Android.

In the past, he has worked on the mobile team at Yelp and as a contractor for Propeller Labs. Jonathan is currently working in the engineering team at Shyp, both on the Android application and the corresponding backend API.

I'd like to thank Packt Publishing for giving me the opportunity to review this educational book that will hopefully simplify the use of Gradle for many developers.

Takuya Miyamoto is a full-stack developer with 6 years of experience in designing, implementing, and maintaining various types of web services and APIs such as e-commerce and SNS. He also has some experience as an Android developer. He has worked as a senior engineer in an enterprise, as a lead engineer in start-ups, and is currently working as an individual developer.

Marco A. Rodriguez-Suarez is the head of mobile at Snapwire, a collaborative platform and marketplace that connects photographers with brands and businesses around the world. Prior to that, he worked in mobile consulting on diverse projects, ranging from topics such as video streaming to game emulation. He has been working with Android since the release of the first public device in 2008 and has been hooked on mobile development ever since. He is passionate about build systems and has extensive experience with Gradle, Maven, and Ant. Marco received his master's degree in electrical engineering from the University of California at Santa Barbara.

Felix Schulze is leading the mobile software development department at AutoScout24 and is responsible for the Android and iOS development. He also gives a lot of talks about continuous integration in app development and contributes to open source tools. His Twitter handle is @x2on; you can also check out his website at www.felixschulze.de.

Hugo Visser has many years of experience as a software engineer, ranging from server-side to desktop and from web to mobile. Since the original announcement, he has closely followed the development of the Android platform, which resulted in his first app in 2009, Rainy Days, which has since been downloaded over 1,000,000 times worldwide.

He runs his own company, Little Robots, which focuses on apps and other clever uses of the Android platform. He has been named the Google Developer Expert for Android by Google and is an organizer of The Dutch Android User Group, which is a community in the Netherlands where Android professionals can meet and share knowledge with each other during monthly meetings.

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Preface

The build process for an Android app is an incredibly complex procedure that involves many tools. To begin with, all the resource files are compiled and referenced in a R.java file, before the Java code is compiled and then converted to Dalvik bytecode by the dex tool. These files are then packaged into an APK file, and that APK file is signed with a debug or release key, before the app can finally be installed onto a device.

Going through all these steps manually would be a tedious and time-consuming undertaking. Luckily, the Android Tools team has continued to provide developers with tools that take care of the entire process, and in 2013, they introduced Gradle as the new preferred build system for Android apps. Gradle is designed in a way that makes it easy to extend builds and plug into the existing build processes. It provides a Groovy-like DSL to declare builds and create tasks, and makes dependency management easy. Additionally, it is completely free and open source.

By now, most Android developers have switched to Gradle, but many do not know how to make the best of it, and are unaware of what can be achieved with just a few lines of code. This book aims to help those developers, and turn them into Gradle power users. Starting with the basics of Gradle in an Android context, this book goes on to cover dependencies, build variants, testing, creating tasks, and more.

What this book covers

Chapter 1, Getting Started with Gradle and Android Studio, explains why Gradle is useful, how to get started with Android Studio, and what the Gradle Wrapper is.

Chapter 2, Basic Build Customization, goes into detail about the Gradle build files and tasks, and shows how to do simple customizations to the build process.

Chapter 3, Managing Dependencies, shows how to use dependencies, both local and remote ones, and explains dependency-related concepts.

Chapter 4, Creating Build Variants, introduces build types and product flavors, explains what the difference between them is, and shows how to use signing configurations.

Chapter 5, Managing Multimodule Builds, explains how to manage app,