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 semantics

In the previous section, I showed you a simple test case that checks if a button text matches a given string. Here is another test case. It performs a click on the button to see if the button text changes as expected:

fun testLetterAfterButtonClickIsB() {

Again, we start by finding the button. performClick() (this is called an action) clicks it. Assert(hasText("B")) checks if the button text is B afterward. Assertions determine if a test passes or fails.

onNodeWithText() (an extension function of SemanticsNodeInteractions Provider) returns a SemanticsNodeInteraction semantics node. The SemanticsNodeInteractionsProvider interface is the main entry point into testing and is typically implemented by a test rule. It defines two methods, as follows:

  • onNode() finds and returns a semantics...