Book Image

Android UI Development with Jetpack Compose

By : Thomas Künneth
Book Image

Android UI Development with Jetpack Compose

By: Thomas Künneth

Overview of this book

Jetpack Compose is Android’s new framework for building fast, beautiful, and reliable native user interfaces. It simplifies and significantly accelerates UI development on Android using the declarative approach. This book will help developers to get hands-on with Jetpack Compose and adopt a modern way of building Android applications. The book is not an introduction to Android development, but it will build on your knowledge of how Android apps are developed. Complete with hands-on examples, this easy-to-follow guide will get you up to speed with the fundamentals of Jetpack Compose such as state hoisting, unidirectional data flow, and composition over inheritance and help you build your own Android apps using Compose. You'll also cover concepts such as testing, animation, and interoperability with the existing Android UI toolkit. By the end of the book, you'll be able to write your own Android apps using Jetpack Compose.
Table of Contents (16 chapters)
Part 1:Fundamentals of Jetpack Compose
Part 2:Building User Interfaces
Part 3:Advanced Topics

Understanding stateful and stateless composable functions

In this section, I will show you the difference between stateful and stateless composable functions. To understand why this is important, let's first focus on the state term. In previous chapters, I described state as data that can change over time. Where the data is held (an SQLite database, a file, or a value inside an object) does not matter. What is important is that the UI must always show the current data. Therefore, if a value changes, the UI must be notified. To achieve this, we use observable types. This is not specific to Jetpack Compose, but a common pattern in many frameworks, programming languages, and platforms. For example, Kotlin supports observables through property delegates:

var counter by observable(-1) { _, oldValue, newValue ->
  println("$oldValue -> $newValue")
for (i in 0..3) counter = i

observable() returns a delegate for a property that can be read and written...