Book Image

Android Development with Kotlin

By : Igor Wojda, Marcin Moskala
Book Image

Android Development with Kotlin

By: Igor Wojda, Marcin Moskala

Overview of this book

Nowadays, improved application development does not just mean building better performing applications. It has become crucial to find improved ways of writing code. Kotlin is a language that helps developers build amazing Android applications easily and effectively. This book discusses Kotlin features in context of Android development. It demonstrates how common examples that are typical for Android development, can be simplified using Kotlin. It also shows all the benefits, improvements and new possibilities provided by this language. The book is divided in three modules that show the power of Kotlin and teach you how to use it properly. Each module present features in different levels of advancement. The first module covers Kotlin basics. This module will lay a firm foundation for the rest of the chapters so you are able to read and understand most of the Kotlin code. The next module dives deeper into the building blocks of Kotlin, such as functions, classes, and function types. You will learn how Kotlin brings many improvements to the table by improving common Java concepts and decreasing code verbosity. The last module presents features that are not present in Java. You will learn how certain tasks can be achieved in simpler ways thanks to Kotlin. Through the book, you will learn how to use Kotlin for Android development. You will get to know and understand most important Kotlin features, and how they can be used. You will be ready to start your own adventure with Android development with Kotlin.
Table of Contents (16 chapters)
Title Page
About the Authors
About the Reviewers
Customer Feedback
Making Your Marvel Gallery Application

Member extension functions and properties

We've seen top-level extension functions and properties, but it is also possible to define them inside a class or object. Extensions defined there are called member extensions, and they are most often used for different kinds of problem than top-level extensions.

Let's start from the simplest use case where member extensions are used. Let's suppose that we need to drop every third element of a list of String. Here is the extension function that allows us to drop every ith element:

    fun List<String>.dropOneEvery(i: Int) = 
        filterIndexed { index, _ -> index % i == (i - 1) } 

The problem with that function is that it should not be extracted as a util extension, because of the following reason:

  • It is not prepared for different types of list (such as a list of User or Int)
  • It is a rarely used function, so it probably won't be used anywhere else in the project

This is why we would want to keep it private, and it is a good idea to keep it...