Book Image

Android Programming with Kotlin for Beginners

By : John Horton
5 (1)
Book Image

Android Programming with Kotlin for Beginners

5 (1)
By: John Horton

Overview of this book

Android is the most popular mobile operating system in the world and Kotlin has been declared by Google as a first-class programming language to build Android apps. With the imminent arrival of the most anticipated Android update, Android 10 (Q), this book gets you started building apps compatible with the latest version of Android. It adopts a project-style approach, where we focus on teaching the fundamentals of Android app development and the essentials of Kotlin by building three real-world apps and more than a dozen mini-apps. The book begins by giving you a strong grasp of how Kotlin and Android work together before gradually moving onto exploring the various Android APIs for building stunning apps for Android with ease. You will learn to make your apps more presentable using different layouts. You will dive deep into Kotlin programming concepts such as variables, functions, data structures, Object-Oriented code, and how to connect your Kotlin code to the UI. You will learn to add multilingual text so that your app is accessible to millions of more potential users. You will learn how animation, graphics, and sound effects work and are implemented in your Android app. By the end of the book, you will have sound knowledge about significant Kotlin programming concepts and start building your own fully featured Android apps.
Table of Contents (33 chapters)
Android Programming with Kotlin for Beginners
Contributors
Preface
Index

Adding custom buttons to the screen


We need to let the user control when to start another drawing and clear the screen of their previous work. We also need the user to be able to decide whether or when to bring the drawing to life. To achieve this, we will add two buttons to the screen, one for each of these tasks.

Add these new properties to the code after the other properties in the LiveDrawingView class:

// These will be used to make simple buttons
private var resetButton: RectF
private var togglePauseButton: RectF

We now have two RectF instances. These objects hold four Float coordinates each, one coordinate for each corner of our two proposed buttons.

We will now add an init block to the LiveDrawingView class and initialize the positions when the LiveDrawingView instance is first created, as follows:

init {
   // Initialize the two buttons
   resetButton = RectF(0f, 0f, 100f, 100f)
   togglePauseButton = RectF(0f, 150f, 100f, 250f)
}

Now we have added actual coordinates for the buttons....