Preface

Jetpack Compose is a paradigm shift in Android development and introduces a lot of new concepts that are essential for any Android developer to learn. It solves a lot of pain points that are associated with Android development, and it is touted to be the default way to build Android apps over the next few years.

Using practical examples, you will learn about the fundamental concepts of Jetpack Compose and how to use them when you build your own Android applications. The book starts with an in-depth explanation of the declarative approach, its differences, and its advantages over traditional UI frameworks. Having laid this foundation, we will get practical and write our first composable functions. After that, we will cover layouts, an important core component of every UI framework. Having mastered them, we will move on to more advanced topics such as animation, testing, and architecture best practices.

The second edition has been thoroughly updated to reflect all changes and additions that were made by Google since the initial stable release. All examples are based on Material 3 (also named Material You).

Who this book is for

This book is for Android developers with existing knowledge of the Kotlin programming language, who would like to learn how to build modern Android user interfaces (UIs) using Jetpack Compose.

What this book covers

Chapter 1, Building Your First Compose App, shows you how to build your first Compose app. Also, important key ideas such as composable functions and using previews are introduced. It is important to whet the appetite by offering early success, so we will build, preview, and run composable functions before digging too deep into details.

Chapter 2, Understanding the Declarative Paradigm, explains how Android UI development was done before Jetpack Compose and what the issues with this “old” approach are. Also, you will discover how composables are different from views and why this is both important and beneficial.

Chapter 3, Exploring the Key Principles of Compose, explores important terminology, concepts, and techniques. Their knowledge is essential to write well-behaving Compose apps.

Chapter 4, Laying Out UI Elements in Compose, examines how the way Jetpack Compose’s layout system works is different compared to the classic Android UI toolkit. This chapter introduces some of the existing layouts. It also shows you how to implement custom layouts. These are needed if the built-in layouts cannot provide the required distribution of UI elements on screen.

Chapter 5, Managing State of Your Composable Functions, details why reacting to state changes is critical to how modern mobile apps work. Jetpack Compose tries to address this need by providing reactive state primitives. This chapter looks at how to use these state primitives and how they work under the hood.

Chapter 6, Building a Real-World App, revisits previously learned concepts and brings them together in one app. Seeing concepts in actual code will help you to understand them and make it easier to reuse in your own programs.

Chapter 7, Exploring App Architecture, further explores ViewModels and how they can help build a solid app architecture. You will learn how to inject objects such as repositories during ViewModel creation and why this is important. The chapter also introduces side effects as a means to trigger or react to changes outside the Compose world.

Chapter 8, Working with Animations, contains a detailed look at animations and transitions. Using them makes apps really shine. Jetpack Compose simplifies the process of adding animation effects greatly over the old view-based approach. This chapter introduces all the relevant APIs.

Chapter 9, Exploring Interoperability APIs, explains how to mix Jetpack Compose and old-fashioned views in one app. Although Jetpack Compose is the UI toolkit of choice for new apps, its powers can be leveraged in existing apps, too. This chapter discusses strategies to combine both declarative and imperative approaches in one app and offers a migration strategy to painlessly update existing UIs to Jetpack Compose.

Chapter 10, Testing and Debugging Compose Apps, explains why testing the UI of a Compose app works differently than testing a view-based UI. Compose uses a more declarative approach to testing. This chapter introduces basic testing scenarios for Compose apps.

Chapter 11, Developing for Different Form Factors, shows you how to write Compose apps that look great not only on smartphones but also on large-screen devices, such as tablets and foldables. It introduces the concept of Window Size Classes and shows you how they are used to organize screen content.

Chapter 12, Bringing Your Compose UI to Different Platforms, shows you how to bring Compose UIs to different platforms such as the desktop (Windows, Linux, or macOS) and the web. It offers a quick introduction to Compose Multiplatform and related technologies such as Kotlin Multiplatform (KMP). You will learn how to take one of the sample apps of the book to the desktop.

To get the most out of this book

Software/hardware covered in the book	Operating system requirements
Android Studio Giraffe or later versions	Windows, macOS, or Linux

If you are using the digital version of this book, we advise you to type the code yourself or access the code from the book’s GitHub repository (a link is available in the next section). Doing so will help you avoid any potential errors related to the copying and pasting of code.

Download the example code files

You can download the example code files for this book from GitHub at https://github.com/PacktPublishing/Android-UI-development-with-Jetpack-Compose-Second-Edition. If there’s an update to the code, it will be updated in the GitHub repository.

We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out!

Conventions used

There are a number of text conventions used throughout this book.

Code in text: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: “Column() contains two children, Button() and Image(). The image is visible only when showImage is true.”

A block of code is set as follows:

class MainActivity : AppCompatActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContent {
      MainView()
    }
  }
}

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

TextField(
    value = name.value,
    onValueChange = {
        name.value = it
    },
    placeholder = {
        Text(text = stringResource(id = R.string.hint))
    },

Any command-line input or output is written as follows:

$ mkdir css
$ cd css

Bold: Indicates a new term, an important word, or words that you see on screen. For instance, words in menus or dialog boxes appear in bold. Here is an example: “To deploy a composable function to a real device or the Android Emulator, click on the Run Preview button.”

Tips or important notes

Appear like this.

Get in touch

Feedback from our readers is always welcome.

General feedback: If you have questions about any aspect of this book, email us at [e-mail] and mention the book title in the subject of your message.

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