In this book, you will learn simple approaches to developing mobile applications for iOS and Android. If your team has to design projects for two of these systems at once, or you plan to move from one system to another, this practical guide will show you how to solve the most common tasks on each of these platforms. The first part presents solutions to common tasks that have to be solved on any platform, such as writing a file to local storage or creating an HTTP request. The second part describes the process of creating an application on each platform using the techniques from the first part. Code examples for Android are presented in two languages ​ ​ - Java and Kotlin, so the book can serve as a cross-reference not only between iOS and AOSP, but also between Java and Kotlin for Android developers. The publication is intended for programmers specializing in developing applications for iOS or Android.