Step-by-Step Guide: Building a Simple Android App with Kotlin

🛠 Step 1: Set Up Your Android Project

1. Open Android Studio (latest stable version recommended).

2. Click on File → New → New Project.

3. Choose Empty Activity.

4. Name your project (e.g., HelloWorld).

5. Select Kotlin as the language.

6. Finish and wait for Gradle to set up your project.

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📄 Step 2: Design the UI

Open the layout file:

app/src/main/res/layout/activity_main.xml

Replace its content with:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/btn_test_button"
        android:text="@string/test_message"
        android:layout_centerInParent="true"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</RelativeLayout>

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📝 Step 3: Add a String Resource

Open:

app/src/main/res/values/strings.xml

Add:

<string name="test_message">Click Me!</string>

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🧩 Step 4: Add Logic with Kotlin

Open:

app/src/main/java/com/helloworld/MainActivity.kt

Replace with:

package com.helloworld

import android.os.Bundle
import android.widget.Button
import android.widget.Toast
import androidx.activity.enableEdgeToEdge
import androidx.appcompat.app.AppCompatActivity
import androidx.core.view.ViewCompat
import androidx.core.view.WindowInsetsCompat

class MainActivity : AppCompatActivity() {
    val mTestButton by lazy { findViewById<Button>(R.id.btn_test_button) }
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        enableEdgeToEdge()
        setContentView(R.layout.activity_main)

        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main)) { v, insets ->
            val systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars())
            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom)
            insets
        }

        mTestButton.setOnClickListener {
            Toast.makeText(this, "Hello world", Toast.LENGTH_SHORT).show()
        }
    }
}

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⚙️ Step 5: Check AndroidManifest.xml

Open:

app/src/main/AndroidManifest.xml

Make sure it includes your launcher activity:

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.HelloWorld"
        tools:targetApi="31">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

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▶️ Step 6: Build & Run

• Connect an Android device or use an emulator.

• Click Run (green ▶ button) in Android Studio.

• Tap the button and see the toast: Hello world.

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📐 What is RelativeLayout and why use it?

RelativeLayout is a view group that lets you place child views relative to each other or to the parent.

Common attributes:

• android:layout_centerInParent="true": centers the view in parent.

• android:layout_below="@id/otherView": places below another view.

• android:layout_alignParentTop="true": aligns to parent top.

It helps simplify layouts instead of nesting multiple LinearLayouts.

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🎉 Congratulations!

You've built your first Kotlin Android app!
Feel free to explore further, and follow for more tutorials!

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