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Android Programming with Kotlin for Beginners

You're reading from   Android Programming with Kotlin for Beginners Build Android apps starting from zero programming experience with the new Kotlin programming language

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Product type Paperback
Published in Apr 2019
Publisher Packt
ISBN-13 9781789615401
Length 698 pages
Edition 1st Edition
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Author (1):
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John Horton John Horton
Author Profile Icon John Horton
John Horton
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Table of Contents (31) Chapters Close

Preface 1. Getting Started with Android and Kotlin FREE CHAPTER 2. Kotlin, XML, and the UI Designer 3. Exploring Android Studio and the Project Structure 4. Getting Started with Layouts and Material Design 5. Beautiful Layouts with CardView and ScrollView 6. The Android Lifecycle 7. Kotlin Variables, Operators, and Expressions 8. Kotlin Decisions and Loops 9. Kotlin Functions 10. Object-Oriented Programming 11. Inheritance in Kotlin 12. Connecting Our Kotlin to the UI and Nullability 13. Bringing Android Widgets to Life 14. Android Dialog Windows 15. Handling Data and Generating Random Numbers 16. Adapters and Recyclers 17. Data Persistence and Sharing 18. Localization 19. Animations and Interpolations 20. Drawing Graphics 21. Threads and Starting the Live Drawing App 22. Particle Systems and Handling Screen Touches 23. Android Sound Effects and the Spinner Widget 24. Design Patterns, Multiple Layouts, and Fragments 25. Advanced UI with Paging and Swiping 26. Advanced UI with Navigation Drawer and Fragment 27. Android Databases 28. A Quick Chat Before You Go A. Other Book You May Enjoy Index

Using the Canvas class

Let's take a look at the code and the different stages that are required to get drawing, then we can quickly move on to drawing something, for real, with the Canvas demo app.

Preparing the instances of the required classes

The first step is to turn the classes that we need into usable instances.

First, we declare all the instances that we require. We can't initialize the instances right away, but we can make sure that we initialize them before they are used, so we use lateinit in the same way we did in the Animation demo app:

// Here are all the objects(instances)
// of classes that we need to do some drawing
lateinit var myImageView: ImageView
lateinit var myBlankBitmap: Bitmap
lateinit var myCanvas: Canvas
lateinit var myPaint: Paint

The previous code declares references of the ImageView, Bitmap, Canvas, and Paint types. They are named myImageView, myBlankBitmap, myCanvas, and myPaint, respectively.

Initializing the objects

Next, we need to initialize our new...

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