Mastering Android Development with Kotlin: Deep dive into the world of Android to create robust applications with Kotlin

Mastering Android Development with Kotlin

Deep dive into the world of Android to create robust applications with Kotlin

Miloš Vasić

BIRMINGHAM - MUMBAI

Mastering Android Development with Kotlin

Copyright © 2017 Packt Publishing

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First published: November 2017

Production reference: 1061117

Published by Packt Publishing Ltd.

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ISBN 978-1-78847-369-9

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Credits

About the Author

Miloš Vasić is a software engineer, author, and open source enthusiast. He holds a bachelor's degree in the programming of computer graphics and a master's degree in the field of Android programming; both degrees were gained at Singidunum University. He published his first book, Fundamental Kotlin, in October 2016, thus achieving his dream of becoming an author. He's currently employed at the Robert Bosch company, where he's working on SDKs for the auto-industry. When he is not working on new books, Miloš works on his open source projects.

Acknowledgments

This book has been a long and fun journey that I would not have manage to accomplish without help. So I think it's only polite to give gratitude.

First of all, I would like to thank my girlfriend and personal assistant, Maja. She was the one who supported me and helped me while writing my first book Fundamental Kotlin and continued to do so with this one. She improved this book greatly by helping me write coherent text that is understandable even for those who are not experienced in programming.

Next I would like to thank my editor at Packt Akshada. She was the best editor I could ask for and she helped me immensely with excellent advices and endless patience. The whole team at Packt that stands behind was book was incredibly supportive and helpful.

Big thanks also to my friends who tolerated me and constantly filled me up with large amounts of coffee. Especially to my friend Vanja Petkovic. He was the technical editor for this book and it wouldn't be the same without him.

And last but not least I would like to thank to my family for supporting me in my dream of becoming software engineer. They were with me and they were patient during all my phases! But, the most important of all, they believed in me!

None of this would be possible if there weren't people who read my first book. I am forever grateful for their support. See you in my next book!

Best wishes,

Miloš

About the Reviewer

Vanja Petkovic studied math and computer science at Belgrade University, Serbia. There, he also obtained his MSc in computer science. He has been working as a software engineer for more than 13 years. Currently, he lives in Switzerland and works for Leica Geosystems in the 3D scanning department. He has specialized in software development for mobile devices and backend services. He started with software development for Palm OS, through Windows Mobile OS and Blackberry OS to Android OS and iOS today. His preferred weapons for developing backend services are Java and Spring.

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Table of Contents

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

Downloading the color images of this book

Errata

Piracy

Questions

Starting with Android

Why Kotlin?

Kotlin for Android - it's official

Downloading and configuring Android Studio

Setting up Android emulators

Creating a new AVD instance

Duplicating an existing AVD and modifying it by need

Android Debug Bridge

Other important tools

Initializing a Git repository

Creating an Android project

Setting up Gradle

Explaining directory structure

Defining build types and flavors

Additional libraries

Getting familiar with Android Manifest

Main Application class

Your first screen

Summary

Building and Running

Running your first Android application

Meet the Logcat

First case

Using the Gradle build tool

Debug your application

Summary

Screens

Analyzing the mockup plan

Defining application activities

Android layouts

Using EditText views

The margins attribute

The padding attribute

Checking out the gravity attribute

Looking at other attributes

Understanding Android Context

Understanding fragments

Fragment manager

Fragments stack

Creating View Pager

Making animations with transitions

Dialog fragments

Notifications

Other important UI components

Summary

Connecting Screen Flow

Creating an application bar

Using the navigation drawer

Connecting activities

Looking deeper into Android Intents

Passing information between activities and fragments

Summary

Look and Feel

Themes in the Android Framework

Styles in Android

Working with assets

Using custom fonts

Applying coloring

Make your buttons look pretty

Setting animations

Animation sets in Android

Summary

Permissions

Permissions from Android Manifest

Requesting permissions

Doing it the Kotlin way

Summary

Working with Databases

Introduction to SQLite

Benefits

Describing our database

CRUD operations

Insert CRUD operation

Update CRUD operation

Delete CRUD operation

Select CRUD operation

Tying things together

Summary

Android Preferences

What are Android preferences?

How can you use them?

Editing (storing) preferences

Removing preferences

Defining your own preferences manager

Summary

Concurrency in Android

Introduction to Android concurrency

Main thread

Handlers and threads

AsyncTask

Understanding Android Looper

Preparing the Looper

Delayed execution

Summary

Android Services

Service categorization

Foreground Android services

Background Android services

Bound Android services

Android service basics

Declaring your service

Starting the service

Stopping the service

Binding to Android service

Stopping the service

Service lifecycle

Defining the main application service

Defining the intent service

Summary

Messaging

Understanding Android broadcasts

System broadcasts

Listening for broadcasts

Registering from the context

Receivers execution

Sending broadcasts

Creating your own broadcast messages

Using on boot and on shutdown broadcasts

Listening for network events

Summary

Backend and API

Identifying entities used

Working with data classes

Connect data models to a database

Introduction to Retrofit

Defining Retrofit service

Building a Retrofit service instance

Introduction to Gson with Kotson library

What else is available?

Retrofit alternative

Gson alternative

Executing our first API call

Content providers

Android adapters

Content loaders

Data binding

Using lists

Using grids

Implementing drag and drop

Summary

Tuning Up for High Performance

Optimizing layouts

Optimizing battery life

Keeping your application responsive

Summary

Testing

Adding dependencies

Updating folder structure

Writing your first test

Using test suites

How to test UI

Running tests

Running unit tests

Running instrumentation tests

Summary

Migration to Kotlin

Preparing the migration

Danger signs

Updating dependencies

Converting classes

Refactoring and cleanup

Summary

Deploying Your Application

Preparing for deployment

Code obfuscation

Signing your application

Publishing to Google Play

Summary

Preface

Android is the most popular platform for mobile devices. Every year, there are more and more developers getting involved in Android development. The Android Framework makes it possible to develop applications for mobile phones, tablets, televisions, and much more! So far, all development has been done in Java. Recently, Google announced Kotlin as the second language developers can use. Because of this, and with Kotlin's ever-growing popularity, we decided to introduce you to Android using Kotlin as its primary development programming language.

With Kotlin, you can do everything you can do with Java, but with more joy and fun! We will show you how to play with Android and Kotlin, and how to create amazing things! Thanks to Kotlin, it's certain that the Android platform will evolve even more. In the near future, it's not impossible that Kotlin will become the primary development language for the platform. Take your seat and get ready for a great journey!

What this book covers

Chapter 1, Starting with Android, teaches you how to start Android development with Kotlin and how to set up your working environment.

Chapter 2, Building and Running, shows you how to build and run your project. It will demonstrate how to log and debug the application.

Chapter 3, Screens, starts with the UI. In this chapter, we will create the first screens for our application.

Chapter 4, Connecting Screen Flow, explains how to connect the screen flow and define basic user interaction with the UI.

Chapter 5, Look and Feel, covers the theming of the UI. We will introduce you to the basic concepts of theming in Android.

Chapter 6, Permissions, explains that in order to take advantage of certain system functionalities, it's necessary to get proper system permissions, which are discussed in this chapter.

Chapter 7, Working with Databases, shows you how to use SQLite as storage for your application. You will create a database to store and share data.

Chapter 8, Android Preferences, states that not all data should be stored in the database; some information can be stored in shared preferences. We will explain why and how.

Chapter 9, Concurrency in Android, explains that if you are familiar with concurrency in programming, then you will know that, in software, many things happen simultaneously. Android is not an exception!

Chapter 10, Android Services, presents Android services and how to use them.

Chapter 11, Messaging, says that in Android, your application can listen for various events. How to do this will be answered in this chapter.

Chapter 12, Backend and API, connects to the remote backend instance to obtain the data.

Chapter 13, Tuning Up for High Performance, is the perfect chapter to give you answers when you are not sure if your application is fast enough.

Chapter 14, Testing, mentions that before we release anything, we must test it. Here, we will explain how to write tests for your application.

Chapter 15, Migration to Kotlin, guides you if you plan to migrate the existing Java code base into Kotlin.

Chapter 16, Deploying Your Application, guides you through the deployment process. We will release everything we develop during this book.

What you need for this book

For this book, a modern computer running Microsoft Windows, Linux, or macOS is required. You will need Java JDK, the Git version-control system, and Android Studio installed.

To run all code examples and the code you write, you will need an Android phone running Android with OS version >= 5.

Who this book is for

The book is aimed at developers who want to build amazing Android applications in an easy and effective way. Basic knowledge of Kotlin is assumed, having no familiarity with Android development.

Conventions

In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, and user input are shown as follows: We will add proper log messages for each lifecycle event of the Application class and the screen (activity) we created.

A block of code is set as follows:

    override fun onCreate(savedInstanceState: Bundle?) {

      super.onCreate(savedInstanceState)

      setContentView(R.layout.activity_main)

      Log.v(tag, [ ON CREATE 1 ])

    }

Any command-line input or output is written as follows. The input command might be broken into several lines to aid readability, but needs to be entered as one continuous line in the prompt:

sudo apt-get install libc6:i386 libncurse

libstdc++6:i386 lib32z1 libbz2-1.0:i386

New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: " Select Tools | Android | AVDManager or click on the AVDManager icon in the toolbar."

Warnings or important notes appear like this.

Tips and tricks appear like this.

Reader feedback

Feedback from our readers is always welcome. Let us know what you think about this book--what you liked or disliked. Reader feedback is important for us as it helps us develop titles that you will really get the most out of.

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Customer support

Now that you are the proud owner of a Packt book, we have a number of things to help you to get the most from your purchase.

Downloading the example code

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The code bundle for the book is also hosted on GitHub at https://github.com/PacktPublishing/-Mastering-Android-Development-with-Kotlin/branches/all. We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out!

Downloading the color images of this book

We also provide you with a PDF file that has color images of the screenshots/diagrams used in this book. The color images will help you better understand the changes in the output. You can download this file from https://www.packtpub.com/sites/default/files/downloads/MasteringAndroidDevelopmentwithKotlin_ColorImages.pdf.

Errata

Although we have taken every care to ensure the accuracy of our content, mistakes do happen. If you find a mistake in one of our books--maybe a mistake in the text or the code--we would be grateful if you could report this to us. By doing so, you can save other readers from frustration and help us improve subsequent versions of this book. If you find any errata, please report them by visiting http://www.packtpub.com/submit-errata, selecting your book, clicking on the Errata Submission Form link, and entering the details of your errata. Once your errata are verified, your submission will be accepted and the errata will be uploaded to our website or added to any list of existing errata under the Errata section of that title.

To view the previously submitted errata, go to https://www.packtpub.com/books/content/support and enter the name of the book in the search field. The required information will appear under the Errata section.

Piracy

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Questions

If you have a problem with any aspect of this book, you can contact us at [email protected], and we will do our best to address the problem.

Starting with Android

Kotlin has been officially announced by Google as a first-class programming language for Android. Find out why Kotlin is the best tool available for you as a newcomer and why senior Android developers first adopted Kotlin.

In this chapter, you will learn how to set up a working environment. You will install and run Android Studio and set up Android SDK and Kotlin. Here, you will also be introduced to some important and useful tools such as Android Debug Bridge (adb).

Since you don't have your project yet, you will set it up. You will initialize a Git repository to track changes in your code and create an empty project. You will enable it to support Kotlin and add support for additional libraries that we will use.

After we have initialized the repository and project, we will go through the project structure and explain each file the IDE has generated. Finally, you will create your first screen and take a look at it.

This chapter will cover the following points:

Setting up an environment for the development of Git and Gradle basics

Working with Android Manifest

Android emulator

Android tools

Why Kotlin?

Before we start our journey, we will answer the question from the chapter title--Why Kotlin? Kotlin is a new programming language developed by JetBrains, the company that developed IntelliJ IDEA. Kotlin is concise and understandable, and it compiles everything to bytecode just like Java. It can also compile to JavaScript or native!

Kotlin comes from professionals of the industry and solves problems programmers are facing every day. It is easy to start and adopt! IntelliJ comes with a Java to Kotlin converter tool. You can convert Java code file by file and everything will still work flawlessly.

It is interoperable and can use any existing Java Framework or library. The interoperability is impeccable and does not require wrappers or adapter layers. Kotlin supports build systems such as Gradle, Maven, Kobalt, Ant, and Griffon with external support.

The most important thing about Kotlin, for us, is that it works perfectly with Android.

Some of the most impressive Kotlin features are as follows:

Null safety

Exceptions are unchecked

Type inference works everywhere

One-liner functions take one line

Generated getters and setter out of the box

We can define functions outside of classes

Data classes

Functional programming support

Extension functions

Kotlin uses Markdown instead of HTML for API documents! The Dokka tool, a Javadoc alternative, can read Kotlin and Java source code and generate combined docs

Kotlin has a better generics support than Java

Reliable and performant concurrent programming

String patterns

Named method arguments

Kotlin for Android - it's official

On May 17th 2017, Google announced that it's making Kotlin, a statically typed programming language for the Java Virtual Machine, a first-class language to write Android apps.

The next version of Android Studio (3.0, current one is 2.3.3) will support Kotlin out of the box. Google will put its effort in the future of Kotlin.

It is important to note that this is only an additional language, not a replacement for existing Java and C++ support (for now).

Downloading and configuring Android Studio

To develop our application, we will need some tools. First of all, we will need an IDE. For that purpose, we will use Android Studio. Android Studio provides the fastest tools to build apps on every type of Android device.

Android Studio offers professional code editing, debugging, and performance tooling. It's a flexible build system that allows you to focus on building a top quality application.

Setting up Android Studio takes just a few clicks. Before we go any further, you need to download the following version for your operating system:

https://developer.android.com/studio/index.html

Here are the instructions for macOS, Linux, and Windows:

macOS:

To install it on macOS, follow these steps:

Launch the Android Studio DMG file.

Drag and drop Android Studio into the Applications folder.

Launch Android Studio.

Select whether you want to import previous Android Studio settings.

Click on OK.

Follow the instructions until Android Studio is ready for use.

Linux:

To install it on Linux, follow these steps:

Unpack the archive you downloaded to an appropriate location for your applications.

Navigate to bin/directory/.

Execute/studio.sh.

Select whether you want to import previous Android Studio settings or not.

Click on OK.

Follow the instructions until Android Studio is ready for use.

Optionally, select Tools | Create Desktop Entry from the menu bar.

If you are running a 64-bit version of Ubuntu, you need to install some 32-bit libraries with the following command:

sudo apt-get install libc6:i386 libncurses5:i386 libstdc++6:i386 lib32z1 libbz2-1.0:i386

In case you are running a 64-bit Fedora, the command is follows:

sudo yum install zlib.i686 ncurses-libs.i686 bzip2-libs.i686

Windows:

To install it on Windows, follow these steps:

Execute the .exe file you downloaded.

Follow the instructions until Android Studio is ready for use.

Setting up Android emulators

Android SDK comes with emulators capable of running applications we develop. We will need it for our project! The purpose of an emulator is to simulate a device and displays all its activity windowed on your computer. What can we do with it? We can prototype, develop, and test--all this without a hardware device. You can emulate phones, tablets, wearables, and TV devices. You can create your own device definitions, or you can use predefined emulators.

The good thing about emulators is that they are fast. In many situations, it will take less time to run an application on an emulator instance than on a real hardware device.

Working with the emulators is just as easy with a real hardware device. For gestures, you use your mouse, and for input, your keyboard.

Emulators can do anything a real phone does! You can easily send incoming phone calls and text messages! You can specify the location of the device, send fingerprint scans, adjust network speed and status, or even simulate battery properties. Emulators can have a virtual SD card and internal data storage, both of them you can use to send real files to that space.

Android Virtual Device (AVD) configuration is used to define an emulator. Each AVD instance works as a completely independent device! For the purpose of creating and management of AVDs, we use the AVD Manager. An AVD definition holds a hardware profile, system image, storage area, skin, and other important properties.

Let's play with it! To run the AVD Manager, do one of the following:

Select Tools | Android | AVDManager or click on the AVDManager icon in the toolbar:

It displays all AVDs you've already defined. As you can see, we don't have any yet!

What