Book Image

How to Build Android Apps with Kotlin - Second Edition

By : Alex Forrester, Eran Boudjnah, Alexandru Dumbravan, Jomar Tigcal
5 (1)
Book Image

How to Build Android Apps with Kotlin - Second Edition

5 (1)
By: Alex Forrester, Eran Boudjnah, Alexandru Dumbravan, Jomar Tigcal

Overview of this book

Looking to kick-start your app development journey with Android 13, but don’t know where to start? How to Build Android Apps with Kotlin is a comprehensive guide that will help jump-start your Android development practice. This book starts with the fundamentals of app development, enabling you to utilize Android Studio and Kotlin to get started with building Android projects. You'll learn how to create apps and run them on virtual devices through guided exercises. Progressing through the chapters, you'll delve into Android's RecyclerView to make the most of lists, images, and maps, and see how to fetch data from a web service. You'll also get to grips with testing, learning how to keep your architecture clean, understanding how to persist data, and gaining basic knowledge of the dependency injection pattern. Finally, you'll see how to publish your apps on the Google Play store. You'll work on realistic projects that are split up into bitesize exercises and activities, allowing you to challenge yourself in an enjoyable and attainable way. You'll build apps to create quizzes, read news articles, check weather reports, store recipes, retrieve movie information, and remind you where you parked your car. By the end of this book, you'll have the skills and confidence to build your own creative Android applications using Kotlin.
Table of Contents (24 chapters)
1
Part 1: Android Foundation
6
Part 2: Displaying Network Calls
12
Part 3: Testing and Code Structure
17
Part 4: Polishing and Publishing an App

Handling user actions

In the previous section, we learned how to build user interfaces using Jetpack Compose. In the exercise, we were unable to collect the data that the user sets in TextField. In this section, we will learn how to handle the user input as well as the state of the user interface.

Let’s assume we have the following example:

@Composable
fun MyScreen() {
    Column { TextField(value = "", onValueChange = {}) }
}

In this example, we define a TextField that is empty and has no handling for the change of the value. As we’ve seen, this won’t let us introduce any new input from the keyboard because it will always set the text to an empty string.

For us to be able to introduce a new text, we will need to create a mutable variable to store the text inside and for it to survive recomposition. In Jetpack Compose, we can use the @Composable function called remember to define a MutableState that will hold our text:

...