How to Build Android Apps with Kotlin: A Beginner’s Guide

Hey there, future app developer! So you want to learn how to build Android apps with Kotlin? You’re in the right place. Let’s dive in and get you started on your journey to creating awesome Android apps.

What’s the Deal with Kotlin?

First things first – why Kotlin? Well, it’s become a big deal in the Android world. Google even made it their preferred language for Android development back in 2019 [1]. It’s modern, it’s concise, and it plays really well with existing Java code. Plus, it’s got some cool features that make coding easier and more fun.

Why Kotlin? The Android Developer’s New Best Friend

Before we jump into the nitty-gritty, let’s talk about why Kotlin has become such a big deal in Android development. Back in 2019, Google made waves by announcing Kotlin as their preferred language for Android app development [1]. But why?

1. Conciseness: Kotlin lets you do more with less code. It’s like Java, but with a lot of the verbosity stripped away.
2. Safety: Null pointer exceptions? Kotlin’s got your back with null safety built into the language.
3. Interoperability: It plays nice with existing Java code, making it easy to adopt in existing projects.
4. Modern features: Things like coroutines for asynchronous programming and data classes make life much easier.

Don’t just take my word for it. According to JetBrains’ 2021 Developer Ecosystem survey, 62% of Android developers are now using Kotlin. That’s a pretty big endorsement!

Setting Up Your Kotlin Android Development Environment

Alright, let’s get you set up to start coding. Here’s what you need:

1. Install Java Development Kit (JDK): Kotlin runs on the Java Virtual Machine (JVM), so you’ll need this. Download it from Oracle’s website [3].
2. Download Android Studio: This is your one-stop-shop for Android development. Get it from the official Android Developer website [4].
3. Install Android Studio: During installation, make sure you select “Custom” and check the box for “Android Virtual Device” to get the emulator.
4. Set up an Android Virtual Device (AVD): Once Android Studio is installed, go to Tools > AVD Manager and create a virtual device for testing.

Pro tip: If you’re using a physical Android device for testing, don’t forget to enable Developer Options and USB Debugging on your device!

Getting Started: Your Toolkit

Before we jump into coding, you’ll need to set up your development environment. Don’t worry, it’s not as scary as it sounds!

1. Install Android Studio: This is your main workspace for building Android apps. You can download it for free from the official Android Developer website [2].
2. Set up Kotlin: Good news! Android Studio comes with Kotlin support built-in. No extra steps needed here.
3. Get an Android device or emulator: You’ll need something to test your apps on. An actual Android phone is great, but Android Studio also comes with a built-in emulator if you don’t have a device handy.

Your First Kotlin Android App

Alright, let’s create something! We’ll start with a simple “Hello World” app to get you familiar with the basics.

1. Open Android Studio and click “Start a new Android Studio project”.
2. Choose “Empty Activity” as your template.
3. Name your project something cool (or just “HelloKotlin” if you’re feeling uninspired).
4. Make sure Kotlin is selected as the language.
5. Click “Finish” and let Android Studio do its thing.

Now, let’s break down what you’re looking at:

• app > java > com.example.hellokotlin > MainActivity: This is your main Kotlin file.
• app > res > layout > activity_main.xml: This is your layout file.
• app > manifests > AndroidManifest.xml: This file describes essential information about your app to the Android build tools, Android operating system, and Google Play.

Congrats! You’ve just created your first Kotlin Android project. Take a moment to look around the files Android Studio generated for you.

Understanding the Basics

Now, let’s break down what you’re looking at:

• MainActivity.kt: This is your main Kotlin file. It’s where the magic happens.
• activity_main.xml: This is your layout file. It’s where you design how your app looks.

Open up MainActivity.kt. You’ll see something like this:

class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) } }

This is the heart of your app. The onCreate function is called when your app starts up. It’s where you set up your user interface and initialize things.

Diving into Kotlin Code

Open up MainActivity.kt. You’ll see something like this:

kotlin
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}

Let’s break this down:

• class MainActivity : AppCompatActivity(): This defines your main activity, which inherits from AppCompatActivity.
• override fun onCreate(...): This is a lifecycle method called when your activity is first created.
• setContentView(R.layout.activity_main): This sets the content view to the layout defined in activity_main.xml.

Making Your App Do Something

Let’s add a button to our app that does something when clicked. Open up activity_main.xml and add this inside the ConstraintLayout:

xmlCopy
    android:id="@+id/helloButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Say Hello"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

Now, let’s make it do something. Go back to MainActivity.kt and add this inside the onCreate function:

findViewById<Button>(R.id.helloButton).setOnClickListener {
    Toast.makeText(this, "Hello, Kotlin!", Toast.LENGTH_SHORT).show()
}

This code finds your button, sets up a click listener, and shows a toast message when the button is clicked.

Run Your App!

Hit the green play button in Android Studio to run your app. You should see a button that, when clicked, shows a “Hello, Kotlin!” message. Pretty cool, right?

Adding Functionality: Let’s Make a Clicker Game

To really understand how Kotlin works in Android development, let’s add some functionality. We’ll make a simple clicker game.

First, update your activity_main.xml:

xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/scoreText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Score: 0"
        android:textSize="24sp"
        app:layout_constraintBottom_toTopOf="@+id/clickButton"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/clickButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click Me!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/scoreText" />

</androidx.constraintlayout.widget.ConstraintLayout>

Now, let’s update MainActivity.kt:

kotlin
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.Button
import android.widget.TextView

class MainActivity : AppCompatActivity() {
    private var score = 0

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val scoreText = findViewById<TextView>(R.id.scoreText)
        val clickButton = findViewById<Button>(R.id.clickButton)

        clickButton.setOnClickListener {
            score++
            scoreText.text = "Score: $score"
        }
    }
}

Let’s break down what’s new:

• We declare a score variable to keep track of clicks.
• We use findViewById to get references to our TextView and Button.
• We set up a click listener on the button that increments the score and updates the TextView.

Kotlin Features Showcase

Now that we have a basic app, let’s showcase some Kotlin features that make Android development easier:

1. Data Classes

Kotlin’s data classes are great for creating model objects. Let’s add a Player class:

kotlin
data class Player(var name: String, var score: Int)

This simple line creates a class with a constructor, getters and setters, toString(), equals(), hashCode(), and copy() methods!

2. Null Safety

Kotlin’s null safety features help prevent null pointer exceptions. Let’s use it in our MainActivity:

kotlin
private var player: Player? = null

override fun onCreate(savedInstanceState: Bundle?) {
    // ... previous code ...

    player = Player("Player 1", 0)

    clickButton.setOnClickListener {
        player?.let {
            it.score++
            scoreText.text = "Score: ${it.score}"
        }
    }
}

The ?. operator and let function ensure we only update the score if player is not null.

3. Extension Functions

Kotlin allows you to add methods to existing classes. Let’s add a toast function to Activity:

kotlin
fun Activity.toast(message: String) {
    Toast.makeText(this, message, Toast.LENGTH_SHORT).show()
}

Now you can use it in your activity like this:

kotlin
clickButton.setOnLongClickListener {
    toast("You've discovered the secret long-press!")
    true
}

4. Coroutines

Kotlin’s coroutines make asynchronous programming much simpler. Let’s add a feature that increases the score automatically every second:

kotlin
import kotlinx.coroutines.*

class MainActivity : AppCompatActivity() {
    private val job = Job()
    private val scope = CoroutineScope(Dispatchers.Main + job)

    // ... previous code ...

    override fun onCreate(savedInstanceState: Bundle?) {
        // ... previous code ...

        scope.launch {
            while(true) {
                delay(1000)
                player?.let {
                    it.score++
                    scoreText.text = "Score: ${it.score}"
                }
            }
        }
    }

    override fun onDestroy() {
        super.onDestroy()
        job.cancel()
    }
}

This launches a coroutine that increases the score every second, and we make sure to cancel it when the activity is destroyed.

Where to Go From Here

Congratulations! You’ve just built your first Android app with Kotlin. But this is just the beginning. Here are some next steps to level up your skills:

1. Learn Kotlin in depth: Check out the official Kotlin documentation [3].
2. Explore Android development concepts: The Android Developer guides are a great resource [4].
3. Try building more complex apps: Start with simple ideas and gradually increase complexity.
4. Join the community: Sites like Stack Overflow and Reddit’s r/androiddev are great for getting help and staying updated.

Remember, learning to code is a journey. Take it one step at a time, be patient with yourself, and most importantly, have fun! Before you know it, you’ll be building amazing Android apps with Kotlin.

Happy coding!

[1] https://android-developers.googleblog.com/2019/05/google-io-2019-empowering-developers-to-build-experiences-on-Android-Play.html
[2] https://developer.android.com/studio
[3] https://kotlinlang.org/docs/home.html
[4] https://developer.android.com/guide

Remember, becoming proficient in Android development with Kotlin is a journey. Take it one step at a time, don’t be afraid to make mistakes, and most importantly, enjoy the process of creating. Before you know it, you’ll be building complex, beautiful Android apps with Kotlin.

Happy coding, future Android developer extraordinaire!