Book Image

Simplifying Android Development with Coroutines and Flows

By : Jomar Tigcal
Book Image

Simplifying Android Development with Coroutines and Flows

By: Jomar Tigcal

Overview of this book

Coroutines and flows are the new recommended way for developers to carry out asynchronous programming in Android using simple, modern, and testable code. This book will teach you how coroutines and flows work and how to use them in building Android applications, along with helping you to develop modern Android applications with asynchronous programming using real data. The book begins by showing you how to create and handle Kotlin coroutines on Android. You’ll explore asynchronous programming in Kotlin, and understand how to test Kotlin coroutines. Next, you'll learn about Kotlin flows on Android, and have a closer look at using Kotlin flows by getting to grips with handling flow cancellations and exceptions and testing the flows. By the end of this book, you'll have the skills you need to build high-quality and maintainable Android applications using coroutines and flows.
Table of Contents (11 chapters)
Part 1 – Kotlin Coroutines on Android
Part 2 – Kotlin Flows on Android

Canceling Kotlin Flows

In this section, we will start by looking at Kotlin Flow cancelations. Like coroutines, Flows can also be canceled manually or automatically.

In Chapter 3, Handling Coroutine Cancelations and Exceptions, we learned about canceling coroutines and that coroutine cancellation must be cooperative. As Kotlin Flows are built on top of coroutines, Flow follows the cooperative cancellation of coroutines.

Flows created using the flow{} builder are cancellable by default. Each emit call to send new values to the Flow also calls ensureActive internally. This checks whether the coroutine is still active, and if not, it will throw CancellationException.

For example, we can use the flow{} builder to create a cancellable Flow, as shown in the following:

class MovieViewModel : ViewModel() {
    fun fetchMovies(): Flow<Movie> = flow {