Code Example for MVVM in Android

Example: Implementing MVVM with ViewModel and LiveData.

Output: The ViewModel loads the user data, and the UI updates when the data is available through LiveData.

Code Example for MVP in Android

Example: Implementing MVP pattern with a unit testable Presenter.

Output: The Presenter loads the user's full name from the Model and displays it on the View (Activity).

Code Example for Clean Architecture in Android

Example: Structuring an Android app with Clean Architecture.

Output: The app is structured with Clean Architecture, separating concerns into different layers. The Presentation layer interacts with the Domain layer to retrieve data and update the UI.

Code Example for Hilt Dependency Injection in Android

Example: Using Hilt for DI in an Android app.

Output: Hilt provides the necessary dependencies (UserRepository) to the Activity, ensuring that the code is decoupled and easier to maintain.

Code Example for Retrofit Integration in Android

Example: Using Retrofit to fetch data from a RESTful API.

Output: Retrofit makes it easy to send network requests to RESTful APIs and handle the responses asynchronously. In this case, we fetch user data based on a user ID.

Code Example for WebSocket Integration in Android using OkHttp

Example: Using OkHttp to set up WebSocket communication.

Output: OkHttp handles the WebSocket connection, allowing the app to send and receive real-time messages over a WebSocket connection.

Code Example for Firebase Realtime Database Integration

Example: Reading and writing data to Firebase Realtime Database.

Output: Firebase Realtime Database stores and synchronizes data in real-time. Changes made on the database are instantly reflected across all clients.

Code Example for Firebase Firestore Integration

Example: Writing and reading data from Firebase Firestore.

Output: Firestore allows for scalable, real-time synchronization and querying of data, enabling complex data operations on the cloud.

Code Example for Custom Animations with MotionLayout

Example: Creating an animation with MotionLayout.

Output: MotionLayout will animate the image view based on the scene defined in the XML, with customizable transitions, animations, and actions.

Code Example for Using NestedScrollView and CoordinatorLayout

Example: Using NestedScrollView and CoordinatorLayout for advanced scroll behavior.

Output: This layout enables smooth scrolling within a NestedScrollView, and the CoordinatorLayout can be used for more complex behaviors like floating action buttons or app bars that respond to scroll events.

Code Example for Using WebView in Android

Example: Embedding a WebView and enabling JavaScript.

Output: The WebView will display the webpage content, and JavaScript can be executed to interact with the web content from the Android application.

Code Example for Setting Up a CI/CD Pipeline with GitHub Actions

Example: Creating a simple GitHub Actions pipeline for building and testing an Android app.

Output: This pipeline automatically builds the Android app using Gradle every time code is pushed to the main branch. It runs on an Ubuntu runner, checks out the code, sets up JDK 11, and then builds the project using Gradle.

Code Example for Automating Deployment with Fastlane

Example: Setting up Fastlane for automatic app deployment to the Google Play Store.

Output: Fastlane will automate the build and deployment process. The app is built and then uploaded to the Google Play Store under the beta track, which makes it available for internal testing.

Code Example for Automating Versioning with Git and Fastlane

Example: Automating versioning and changelog generation with Git and Fastlane.

Output: Fastlane will automatically increment the version code for each release and generate a changelog based on recent Git commits, which can be used for release notes when deploying the app to the Google Play Store.

Hello World in Kotlin

        // MainActivity.kt
        package com.example.helloworld

        import android.os.Bundle
        import androidx.appcompat.app.AppCompatActivity

        // Main activity class inheriting from AppCompatActivity
        class MainActivity : AppCompatActivity() {
        
            // onCreate method which is called when the activity is created
            override fun onCreate(savedInstanceState: Bundle?) {
                super.onCreate(savedInstanceState)
                // Set the layout for this activity
                setContentView(R.layout.activity_main)
                // Display "Hello, World!" in the console
                println("Hello, World!")
            }
        }
        

Output: "Hello, World!" will be printed in the log.

Simple Button Click Listener

        // MainActivity.kt
        package com.example.buttonclick

        import android.os.Bundle
        import android.widget.Button
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {
        
            override fun onCreate(savedInstanceState: Bundle?) {
                super.onCreate(savedInstanceState)
                setContentView(R.layout.activity_main)
                val button = findViewById<Button>(R.id.button)
                button.setOnClickListener {
                    // Display a Toast message when the button is clicked
                    Toast.makeText(applicationContext, "Button Clicked!", Toast.LENGTH_SHORT).show()
                }
            }
        }
        

Output: A toast message saying "Button Clicked!" will appear on the screen.

Displaying an AlertDialog

        // MainActivity.kt
        package com.example.alertdialog

        import android.os.Bundle
        import android.widget.Button
        import androidx.appcompat.app.AlertDialog
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {
        
            override fun onCreate(savedInstanceState: Bundle?) {
                super.onCreate(savedInstanceState)
                setContentView(R.layout.activity_main)
                val button = findViewById<Button>(R.id.button)
                button.setOnClickListener {
                    // Build and show an AlertDialog
                    val builder = AlertDialog.Builder(this)
                    builder.setTitle("Alert")
                    builder.setMessage("This is an Alert Dialog")
                    builder.setPositiveButton("OK") { dialog, which -> dialog.dismiss() }
                    builder.show()
                }
            }
        }
        

Output: An AlertDialog will pop up with a message "This is an Alert Dialog" and a "OK" button.

Simple TextView Update

        // MainActivity.kt
        package com.example.textviewupdate

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

        class MainActivity : AppCompatActivity() {
        
            override fun onCreate(savedInstanceState: Bundle?) {
                super.onCreate(savedInstanceState)
                setContentView(R.layout.activity_main)
                val textView = findViewById(R.id.textView)
                // Update the TextView's text dynamically
                textView.text = "Updated Text!"
            }
        }
        

Output: The TextView will display "Updated Text!" on the screen.

Toast Message Example

        // MainActivity.kt
        package com.example.toastmessage

        import android.os.Bundle
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {
        
            override fun onCreate(savedInstanceState: Bundle?) {
                super.onCreate(savedInstanceState)
                setContentView(R.layout.activity_main)
                // Show a Toast message when activity starts
                Toast.makeText(applicationContext, "Welcome!", Toast.LENGTH_LONG).show()
            }
        }
        

Output: A Toast message saying "Welcome!" will appear on the screen.

Switch Button to Toggle Visibility

        // MainActivity.kt
        package com.example.togglevisibility

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

        class MainActivity : AppCompatActivity() {
        
            override fun onCreate(savedInstanceState: Bundle?) {
                super.onCreate(savedInstanceState)
                setContentView(R.layout.activity_main)
                val switch = findViewById(R.id.switchButton)
                val textView = findViewById(R.id.textView)
                
                switch.setOnCheckedChangeListener { _, isChecked ->
                    // Toggle visibility based on switch state
                    textView.visibility = if (isChecked) android.view.View.VISIBLE else android.view.View.INVISIBLE
                }
            }
        }
        

Output: The TextView will toggle its visibility based on the Switch button's state.

RecyclerView with Simple Adapter

        // MainActivity.kt
        package com.example.recyclerview

        import android.os.Bundle
        import android.view.LayoutInflater
        import android.view.View
        import android.view.ViewGroup
        import android.widget.TextView
        import androidx.appcompat.app.AppCompatActivity
        import androidx.recyclerview.widget.LinearLayoutManager
        import androidx.recyclerview.widget.RecyclerView

        class MainActivity : AppCompatActivity() {

            override fun onCreate(savedInstanceState: Bundle?) {
                super.onCreate(savedInstanceState)
                setContentView(R.layout.activity_main)
                
                val recyclerView = findViewById(R.id.recyclerView)
                recyclerView.layoutManager = LinearLayoutManager(this)
                recyclerView.adapter = SimpleAdapter(listOf("Item 1", "Item 2", "Item 3"))
            }
            
            // Adapter class for RecyclerView
            class SimpleAdapter(private val items: List) : RecyclerView.Adapter() {

                override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
                    val view = LayoutInflater.from(parent.context).inflate(android.R.layout.simple_list_item_1, parent, false)
                    return ViewHolder(view)
                }

                override fun onBindViewHolder(holder: ViewHolder, position: Int) {
                    holder.textView.text = items[position]
                }

                override fun getItemCount(): Int = items.size
                
                // ViewHolder class to hold references to the views
                class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
                    val textView: TextView = itemView.findViewById(android.R.id.text1)
                }
            }
        }
        

Output: A RecyclerView will display a list of items: "Item 1", "Item 2", "Item 3".

Working with SharedPreferences

        // MainActivity.kt
        package com.example.sharedpreferences

        import android.content.SharedPreferences
        import android.os.Bundle
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                // Get SharedPreferences
                val sharedPreferences: SharedPreferences = getSharedPreferences("MyPrefs", MODE_PRIVATE)
                // Save data to SharedPreferences
                val editor = sharedPreferences.edit()
                editor.putString("username", "john_doe")
                editor.apply()

                // Retrieve data from SharedPreferences
                val username = sharedPreferences.getString("username", "default_name")
            }
        }
        

Output: The username "john_doe" will be saved and retrieved from SharedPreferences.

SQLite Database CRUD Operations

        // DatabaseHelper.kt
        package com.example.sqldatabase

        import android.content.Context
        import android.database.sqlite.SQLiteDatabase
        import android.database.sqlite.SQLiteOpenHelper

        class DatabaseHelper(context: Context) : SQLiteOpenHelper(context, "users.db", null, 1) {

            override fun onCreate(db: SQLiteDatabase) {
                // Create a new table
                val createTableQuery = "CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT)"
                db.execSQL(createTableQuery)
            }

            override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
                db.execSQL("DROP TABLE IF EXISTS users")
                onCreate(db)
            }
        }

        // MainActivity.kt
        package com.example.sqldatabase

        import android.os.Bundle
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val dbHelper = DatabaseHelper(this)
                val db = dbHelper.writableDatabase

                // Insert a new user into the database
                val insertQuery = "INSERT INTO users (name) VALUES ('John Doe')"
                db.execSQL(insertQuery)

                // Read data from the database
                val cursor = db.rawQuery("SELECT * FROM users", null)
                if (cursor.moveToFirst()) {
                    val username = cursor.getString(cursor.getColumnIndex("name"))
                    Toast.makeText(applicationContext, "User: $username", Toast.LENGTH_LONG).show()
                }
            }
        }
        

Output: A new user will be inserted into the SQLite database, and their name will be shown in a Toast message.

Image Loading with Glide

        // MainActivity.kt
        package com.example.imageloader

        import android.os.Bundle
        import android.widget.ImageView
        import androidx.appcompat.app.AppCompatActivity
        import com.bumptech.glide.Glide

        class MainActivity : AppCompatActivity() {

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

                val imageView = findViewById(R.id.imageView)
                // Load an image from URL using Glide
                Glide.with(this)
                    .load("https://example.com/image.jpg")
                    .into(imageView)
            }
        }
        

Output: The image from the provided URL will be displayed in the ImageView.

Basic Retrofit API Request

        // MainActivity.kt
        package com.example.retrofit

        import android.os.Bundle
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity
        import retrofit2.Call
        import retrofit2.Callback
        import retrofit2.Response
        import retrofit2.Retrofit
        import retrofit2.converter.gson.GsonConverterFactory

        interface ApiService {
            @GET("users/1")
            fun getUser(): Call
        }

        data class User(val id: Int, val name: String)

        class MainActivity : AppCompatActivity() {

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

                val retrofit = Retrofit.Builder()
                    .baseUrl("https://jsonplaceholder.typicode.com/")
                    .addConverterFactory(GsonConverterFactory.create())
                    .build()

                val apiService = retrofit.create(ApiService::class.java)
                apiService.getUser().enqueue(object : Callback {
                    override fun onResponse(call: Call, response: Response) {
                        if (response.isSuccessful) {
                            val user = response.body()
                            Toast.makeText(applicationContext, "User: ${user?.name}", Toast.LENGTH_LONG).show()
                        }
                    }

                    override fun onFailure(call: Call, t: Throwable) {
                        Toast.makeText(applicationContext, "Error: ${t.message}", Toast.LENGTH_LONG).show()
                    }
                })
            }
        }
        

Output: The app will show a Toast message with the user's name retrieved from the API.

JSON Parsing with Gson

        // MainActivity.kt
        package com.example.jsonparsing

        import android.os.Bundle
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity
        import com.google.gson.Gson
        import com.google.gson.JsonObject

        class MainActivity : AppCompatActivity() {

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

                val json = """{"name": "John", "age": 30}"""
                val gson = Gson()
                val user = gson.fromJson(json, User::class.java)

                // Display parsed data in a Toast
                Toast.makeText(applicationContext, "Name: ${user.name}, Age: ${user.age}", Toast.LENGTH_LONG).show()
            }
        }

        data class User(val name: String, val age: Int)
        

Output: A Toast message showing "Name: John, Age: 30" will appear.

Handling Orientation Changes

        // AndroidManifest.xml
        

        // MainActivity.kt
        package com.example.orientation

        import android.os.Bundle
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                // Check orientation change and handle accordingly
                if (resources.configuration.orientation == 1) {
                    // Portrait mode
                } else {
                    // Landscape mode
                }
            }
        }
        

Output: The app will handle orientation changes (portrait/landscape).

Snackbar for Action Feedback

        // MainActivity.kt
        package com.example.snackbar

        import android.os.Bundle
        import android.view.View
        import androidx.appcompat.app.AppCompatActivity
        import com.google.android.material.snackbar.Snackbar

        class MainActivity : AppCompatActivity() {

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

                val rootView = findViewById(R.id.rootView)
                val snackbar = Snackbar.make(rootView, "Action performed", Snackbar.LENGTH_LONG)
                snackbar.setAction("Undo") {
                    // Perform undo action
                }
                snackbar.show()
            }
        }
        

Output: A Snackbar will show with an "Undo" action that can be clicked to perform an undo operation.

Simple ProgressBar Implementation

        // MainActivity.kt
        package com.example.progressbar

        import android.os.Bundle
        import android.widget.ProgressBar
        import android.widget.Button
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val progressBar = findViewById(R.id.progressBar)
                val button = findViewById<Button>(R.id.button)

                button.setOnClickListener {
                    // Start progress bar animation
                    progressBar.visibility = android.view.View.VISIBLE
                    progressBar.progress = 50
                }
            }
        }
        

Output: The ProgressBar will show and fill to 50% when the button is clicked.

FloatingActionButton with Animation

        // MainActivity.kt
        package com.example.fabanimation

        import android.os.Bundle
        import android.view.animation.AnimationUtils
        import androidx.appcompat.app.AppCompatActivity
        import com.google.android.material.floatingactionbutton.FloatingActionButton

        class MainActivity : AppCompatActivity() {

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

                val fab = findViewById(R.id.fab)
                val rotateAnimation = AnimationUtils.loadAnimation(this, R.anim.rotate)

                fab.setOnClickListener {
                    // Apply animation to FloatingActionButton
                    fab.startAnimation(rotateAnimation)
                }
            }
        }
        

Output: The FloatingActionButton will rotate when clicked.

Using DatePickerDialog

        // MainActivity.kt
        package com.example.datepicker

        import android.app.DatePickerDialog
        import android.os.Bundle
        import android.widget.Button
        import android.widget.TextView
        import androidx.appcompat.app.AppCompatActivity
        import java.util.*

        class MainActivity : AppCompatActivity() {

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

                val button = findViewById<Button>(R.id.button)
                val textView = findViewById(R.id.textView)

                button.setOnClickListener {
                    // Show DatePickerDialog
                    val calendar = Calendar.getInstance()
                    val datePickerDialog = DatePickerDialog(this, { _, year, month, dayOfMonth ->
                        textView.text = "Selected Date: $dayOfMonth/$month/$year"
                    }, calendar.get(Calendar.YEAR), calendar.get(Calendar.MONTH), calendar.get(Calendar.DAY_OF_MONTH))
                    datePickerDialog.show()
                }
            }
        }
        

Output: The selected date will be displayed in the TextView after picking a date from the DatePickerDialog.

Saving File to Internal Storage

        // MainActivity.kt
        package com.example.filestorage

        import android.os.Bundle
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity
        import java.io.FileOutputStream

        class MainActivity : AppCompatActivity() {

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

                val filename = "myfile.txt"
                val fileContents = "Hello, Android!"
                
                // Write to a file in internal storage
                openFileOutput(filename, MODE_PRIVATE).use {
                    it.write(fileContents.toByteArray())
                    Toast.makeText(applicationContext, "File Saved", Toast.LENGTH_SHORT).show()
                }
            }
        }
        

Output: A file named "myfile.txt" will be saved in the internal storage with the text "Hello, Android!".

Simple Firebase Authentication Example

        // MainActivity.kt
        package com.example.firebaseauth

        import android.os.Bundle
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity
        import com.google.firebase.auth.FirebaseAuth

        class MainActivity : AppCompatActivity() {

            private lateinit var auth: FirebaseAuth

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

                auth = FirebaseAuth.getInstance()
                val email = "user@example.com"
                val password = "password123"
                
                // Firebase Authentication for login
                auth.signInWithEmailAndPassword(email, password)
                    .addOnCompleteListener(this) { task ->
                        if (task.isSuccessful) {
                            // Sign-in success
                            Toast.makeText(applicationContext, "Login Successful", Toast.LENGTH_SHORT).show()
                        } else {
                            // Sign-in failure
                            Toast.makeText(applicationContext, "Authentication Failed", Toast.LENGTH_SHORT).show()
                        }
                    }
            }
        }
        

Output: A Toast message will appear indicating whether the login was successful or failed.

Handling Multiple Permissions Requests

        // MainActivity.kt
        package com.example.permissions

        import android.Manifest
        import android.content.pm.PackageManager
        import android.os.Bundle
        import androidx.appcompat.app.AppCompatActivity
        import androidx.core.app.ActivityCompat
        import androidx.core.content.ContextCompat

        class MainActivity : AppCompatActivity() {

            private val PERMISSION_REQUEST_CODE = 1

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

                // Check and request permissions
                if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                    ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.CAMERA), PERMISSION_REQUEST_CODE)
                }
            }
        }
        

Output: If the permission is not granted, a request dialog will pop up asking for the CAMERA permission.

Simple Calculator App

        // MainActivity.kt
        package com.example.calculator

        import android.os.Bundle
        import android.widget.Button
        import android.widget.EditText
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val editText = findViewById(R.id.editText)
                val btnAdd = findViewById<Button>(R.id.btnAdd)
                val btnSubtract = findViewById<Button>(R.id.btnSubtract)

                btnAdd.setOnClickListener {
                    val num1 = editText.text.toString().toInt()
                    val num2 = 10 // Example value
                    editText.setText((num1 + num2).toString())
                }

                btnSubtract.setOnClickListener {
                    val num1 = editText.text.toString().toInt()
                    val num2 = 5 // Example value
                    editText.setText((num1 - num2).toString())
                }
            }
        }
        

Output: The calculator will perform addition and subtraction on the number entered in the EditText when the respective buttons are clicked.

To-Do List with Checkboxes

        // MainActivity.kt
        package com.example.todo

        import android.os.Bundle
        import android.widget.CheckBox
        import android.widget.LinearLayout
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val layout = findViewById(R.id.layout)

                val task = CheckBox(this)
                task.text = "Finish Homework"
                task.setOnCheckedChangeListener { _, isChecked ->
                    if (isChecked) {
                        Toast.makeText(this, "Task Completed!", Toast.LENGTH_SHORT).show()
                    }
                }

                layout.addView(task)
            }
        }
        

Output: A checkbox will be displayed, and once checked, it will show a Toast message saying "Task Completed!"

Stopwatch App

        // MainActivity.kt
        package com.example.stopwatch

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

        class MainActivity : AppCompatActivity() {

            private var seconds = 0
            private lateinit var handler: Handler
            private lateinit var runnable: Runnable

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

                val textView = findViewById(R.id.textView)
                val startButton = findViewById<Button>(R.id.startButton)
                val stopButton = findViewById<Button>(R.id.stopButton)

                handler = Handler()

                startButton.setOnClickListener {
                    runnable = Runnable {
                        seconds++
                        textView.text = seconds.toString()
                        handler.postDelayed(runnable, 1000)
                    }
                    handler.post(runnable)
                }

                stopButton.setOnClickListener {
                    handler.removeCallbacks(runnable)
                }
            }
        }
        

Output: The stopwatch will display seconds incrementing every second and stop when the "Stop" button is clicked.

Basic Weather App (using a public API)

        // MainActivity.kt
        package com.example.weatherapp

        import android.os.Bundle
        import android.widget.TextView
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity
        import okhttp3.OkHttpClient
        import okhttp3.Request
        import org.json.JSONObject

        class MainActivity : AppCompatActivity() {

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

                val textView = findViewById(R.id.textView)

                val client = OkHttpClient()
                val request = Request.Builder()
                    .url("https://api.openweathermap.org/data/2.5/weather?q=London&appid=YOUR_API_KEY")
                    .build()

                client.newCall(request).enqueue(object : okhttp3.Callback {
                    override fun onResponse(call: okhttp3.Call, response: okhttp3.Response) {
                        val body = response.body?.string()
                        val json = JSONObject(body)
                        val temp = json.getJSONObject("main").getDouble("temp")
                        runOnUiThread {
                            textView.text = "Temperature: $temp°C"
                        }
                    }

                    override fun onFailure(call: okhttp3.Call, e: java.io.IOException) {
                        runOnUiThread {
                            Toast.makeText(applicationContext, "Error: ${e.message}", Toast.LENGTH_SHORT).show()
                        }
                    }
                })
            }
        }
        

Output: The temperature of the specified city will be fetched and displayed in the TextView.

Simple Tip Calculator

        // MainActivity.kt
        package com.example.tipcalculator

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

        class MainActivity : AppCompatActivity() {

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

                val amountEditText = findViewById(R.id.amountEditText)
                val tipTextView = findViewById(R.id.tipTextView)
                val calculateButton = findViewById<Button>(R.id.calculateButton)

                calculateButton.setOnClickListener {
                    val amount = amountEditText.text.toString().toDouble()
                    val tip = amount * 0.15
                    tipTextView.text = "Tip: $tip"
                }
            }
        }
        

Output: The app will calculate a 15% tip based on the input amount and display it in the TextView.

Currency Converter

        // MainActivity.kt
        package com.example.currencyconverter

        import android.os.Bundle
        import android.widget.Button
        import android.widget.EditText
        import android.widget.TextView
        import androidx.appcompat.app.AppCompatActivity
        import okhttp3.OkHttpClient
        import okhttp3.Request
        import org.json.JSONObject

        class MainActivity : AppCompatActivity() {

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

                val amountEditText = findViewById(R.id.amountEditText)
                val resultTextView = findViewById(R.id.resultTextView)
                val convertButton = findViewById<Button>(R.id.convertButton)

                convertButton.setOnClickListener {
                    val amount = amountEditText.text.toString().toDouble()

                    val client = OkHttpClient()
                    val request = Request.Builder()
                        .url("https://api.exchangerate-api.com/v4/latest/USD")
                        .build()

                    client.newCall(request).enqueue(object : okhttp3.Callback {
                        override fun onResponse(call: okhttp3.Call, response: okhttp3.Response) {
                            val body = response.body?.string()
                            val json = JSONObject(body)
                            val rate = json.getJSONObject("rates").getDouble("EUR")
                            val result = amount * rate
                            runOnUiThread {
                                resultTextView.text = "Converted: $result EUR"
                            }
                        }

                        override fun onFailure(call: okhttp3.Call, e: java.io.IOException) {
                            runOnUiThread {
                                resultTextView.text = "Error: ${e.message}"
                            }
                        }
                    })
                }
            }
        }
        

Output: The currency will be converted from USD to EUR and displayed in the TextView.

Flashlight App

        // MainActivity.kt
        package com.example.flashlight

        import android.os.Bundle
        import android.widget.Button
        import android.hardware.camera2.CameraManager
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val cameraManager = getSystemService(CAMERA_SERVICE) as CameraManager
                val cameraId = cameraManager.cameraIdList[0]
                val button = findViewById<Button>(R.id.button)

                button.setOnClickListener {
                    cameraManager.setTorchMode(cameraId, true)
                    Toast.makeText(this, "Flashlight ON", Toast.LENGTH_SHORT).show()
                }
            }
        }
        

Output: The flashlight will be turned on when the button is clicked, and a Toast message will display "Flashlight ON".

Simple Alarm Clock

        // MainActivity.kt
        package com.example.alarmclock

        import android.os.Bundle
        import android.widget.Button
        import android.widget.Toast
        import android.app.AlarmManager
        import android.app.PendingIntent
        import android.content.Intent
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val button = findViewById<Button>(R.id.setAlarmButton)
                button.setOnClickListener {
                    val alarmManager = getSystemService(ALARM_SERVICE) as AlarmManager
                    val alarmIntent = Intent(this, AlarmReceiver::class.java)
                    val pendingIntent = PendingIntent.getBroadcast(this, 0, alarmIntent, 0)

                    val triggerTime = System.currentTimeMillis() + 5000 // 5 seconds from now
                    alarmManager.setExact(AlarmManager.RTC_WAKEUP, triggerTime, pendingIntent)

                    Toast.makeText(this, "Alarm set!", Toast.LENGTH_SHORT).show()
                }
            }
        }
        

Output: The alarm will be set for 5 seconds later, and a Toast message will confirm the alarm is set.

Login Form with Validation

        // MainActivity.kt
        package com.example.loginform

        import android.os.Bundle
        import android.widget.Button
        import android.widget.EditText
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val usernameEditText = findViewById(R.id.username)
                val passwordEditText = findViewById(R.id.password)
                val loginButton = findViewById<Button>(R.id.loginButton)

                loginButton.setOnClickListener {
                    val username = usernameEditText.text.toString()
                    val password = passwordEditText.text.toString()

                    if (username == "admin" && password == "password") {
                        Toast.makeText(this, "Login Successful", Toast.LENGTH_SHORT).show()
                    } else {
                        Toast.makeText(this, "Invalid Credentials", Toast.LENGTH_SHORT).show()
                    }
                }
            }
        }
        

Output: If the username and password are correct, a success Toast will be shown. Otherwise, an error Toast will display.

Basic Contact List with RecyclerView

        // MainActivity.kt
        package com.example.contactlist

        import android.os.Bundle
        import android.widget.LinearLayout
        import androidx.appcompat.app.AppCompatActivity
        import androidx.recyclerview.widget.LinearLayoutManager
        import androidx.recyclerview.widget.RecyclerView

        class MainActivity : AppCompatActivity() {

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

                val recyclerView = findViewById(R.id.recyclerView)
                val contactList = listOf("John", "Jane", "Mark", "Lucy")

                val adapter = ContactAdapter(contactList)
                recyclerView.layoutManager = LinearLayoutManager(this)
                recyclerView.adapter = adapter
            }
        }
        

Output: A RecyclerView will display a list of contacts (names) in a vertical list.

Random Joke Generator App

        // MainActivity.kt
        package com.example.jokegenerator

        import android.os.Bundle
        import android.widget.Button
        import android.widget.TextView
        import androidx.appcompat.app.AppCompatActivity
        import okhttp3.OkHttpClient
        import okhttp3.Request
        import org.json.JSONObject

        class MainActivity : AppCompatActivity() {

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

                val jokeTextView = findViewById(R.id.jokeTextView)
                val generateButton = findViewById<Button>(R.id.generateButton)

                val client = OkHttpClient()

                generateButton.setOnClickListener {
                    val request = Request.Builder()
                        .url("https://official-joke-api.appspot.com/random_joke")
                        .build()

                    client.newCall(request).enqueue(object : okhttp3.Callback {
                        override fun onResponse(call: okhttp3.Call, response: okhttp3.Response) {
                            val body = response.body?.string()
                            val json = JSONObject(body)
                            val setup = json.getString("setup")
                            val punchline = json.getString("punchline")

                            runOnUiThread {
                                jokeTextView.text = "$setup\n\n$punchline"
                            }
                        }

                        override fun onFailure(call: okhttp3.Call, e: java.io.IOException) {
                            runOnUiThread {
                                jokeTextView.text = "Error fetching joke"
                            }
                        }
                    })
                }
            }
        }
        

Output: A random joke will be fetched from the API and displayed when the button is clicked.

Simple Countdown Timer

        // MainActivity.kt
        package com.example.countdowntimer

        import android.os.Bundle
        import android.os.CountDownTimer
        import android.widget.TextView
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val textView = findViewById(R.id.textView)

                object : CountDownTimer(60000, 1000) {
                    override fun onTick(millisUntilFinished: Long) {
                        val secondsRemaining = millisUntilFinished / 1000
                        textView.text = "$secondsRemaining seconds remaining"
                    }

                    override fun onFinish() {
                        textView.text = "Time's up!"
                    }
                }.start()
            }
        }
        

Output: The countdown will start from 60 seconds and update every second until it reaches zero.

Unit Converter (Length, Weight, Volume)

        // MainActivity.kt
        package com.example.unitconverter

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

        class MainActivity : AppCompatActivity() {

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

                val inputEditText = findViewById(R.id.inputEditText)
                val outputTextView = findViewById(R.id.outputTextView)
                val convertButton = findViewById<Button>(R.id.convertButton)

                convertButton.setOnClickListener {
                    val input = inputEditText.text.toString().toDouble()
                    val result = input * 2.54 // Example conversion from inches to cm
                    outputTextView.text = "$input inches = $result cm"
                }
            }
        }
        

Output: The app will convert an input value from inches to centimeters and display the result.

Simple Notes App with SQLite

        // NotesDatabaseHelper.kt
        package com.example.notesapp

        import android.content.Context
        import android.database.sqlite.SQLiteDatabase
        import android.database.sqlite.SQLiteOpenHelper

        class NotesDatabaseHelper(context: Context) :
            SQLiteOpenHelper(context, "notes.db", null, 1) {

            override fun onCreate(db: SQLiteDatabase) {
                db.execSQL("CREATE TABLE notes (id INTEGER PRIMARY KEY, title TEXT, content TEXT)")
            }

            override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
                db.execSQL("DROP TABLE IF EXISTS notes")
                onCreate(db)
            }
        }

        // MainActivity.kt
        package com.example.notesapp

        import android.os.Bundle
        import android.widget.Button
        import android.widget.EditText
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity
        import androidx.recyclerview.widget.RecyclerView

        class MainActivity : AppCompatActivity() {

            private lateinit var dbHelper: NotesDatabaseHelper

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

                dbHelper = NotesDatabaseHelper(this)

                val titleEditText = findViewById(R.id.titleEditText)
                val contentEditText = findViewById(R.id.contentEditText)
                val saveButton = findViewById<Button>(R.id.saveButton)

                saveButton.setOnClickListener {
                    val title = titleEditText.text.toString()
                    val content = contentEditText.text.toString()
                    val db = dbHelper.writableDatabase
                    db.execSQL("INSERT INTO notes (title, content) VALUES (?, ?)", arrayOf(title, content))
                    Toast.makeText(this, "Note Saved", Toast.LENGTH_SHORT).show()
                }
            }
        }
        

Output: Notes will be saved to the SQLite database and a confirmation Toast message will appear.

Gallery App to Display Images from Storage

        // MainActivity.kt
        package com.example.galleryapp

        import android.content.Intent
        import android.net.Uri
        import android.os.Bundle
        import android.provider.MediaStore
        import android.widget.Button
        import android.widget.ImageView
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val imageView = findViewById(R.id.imageView)
                val chooseButton = findViewById<Button>(R.id.chooseButton)

                chooseButton.setOnClickListener {
                    val intent = Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI)
                    startActivityForResult(intent, 100)
                }
            }

            override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
                super.onActivityResult(requestCode, resultCode, data)
                if (requestCode == 100 && resultCode == RESULT_OK) {
                    val selectedImage: Uri? = data?.data
                    val imageView = findViewById(R.id.imageView)
                    imageView.setImageURI(selectedImage)
                }
            }
        }
        

Output: The app will allow the user to select an image from their storage and display it in the ImageView.

Simple Quiz App

        // MainActivity.kt
        package com.example.quizapp

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

        class MainActivity : AppCompatActivity() {

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

                val questionTextView = findViewById(R.id.questionTextView)
                val option1RadioButton = findViewById(R.id.option1RadioButton)
                val option2RadioButton = findViewById(R.id.option2RadioButton)
                val submitButton = findViewById<Button>(R.id.submitButton)

                questionTextView.text = "What is 2 + 2?"
                option1RadioButton.text = "3"
                option2RadioButton.text = "4"

                submitButton.setOnClickListener {
                    if (option2RadioButton.isChecked) {
                        Toast.makeText(this, "Correct Answer!", Toast.LENGTH_SHORT).show()
                    } else {
                        Toast.makeText(this, "Wrong Answer", Toast.LENGTH_SHORT).show()
                    }
                }
            }
        }
        

Output: A simple quiz question will be displayed with two options. A Toast will indicate whether the answer is correct or not.

BMI Calculator

        // MainActivity.kt
        package com.example.bmicalculator

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

        class MainActivity : AppCompatActivity() {

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

                val heightEditText = findViewById(R.id.heightEditText)
                val weightEditText = findViewById(R.id.weightEditText)
                val resultTextView = findViewById(R.id.resultTextView)
                val calculateButton = findViewById<Button>(R.id.calculateButton)

                calculateButton.setOnClickListener {
                    val height = heightEditText.text.toString().toFloat()
                    val weight = weightEditText.text.toString().toFloat()
                    val bmi = weight / (height * height)
                    resultTextView.text = "Your BMI is: $bmi"
                }
            }
        }
        

Output: The BMI is calculated and displayed when the user inputs their weight and height.

Simple Camera App to Take Photos

        // MainActivity.kt
        package com.example.cameraapp

        import android.content.Intent
        import android.os.Bundle
        import android.provider.MediaStore
        import android.widget.Button
        import android.widget.ImageView
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val cameraButton = findViewById<Button>(R.id.cameraButton)
                val imageView = findViewById(R.id.imageView)

                cameraButton.setOnClickListener {
                    val intent = Intent(MediaStore.ACTION_IMAGE_CAPTURE)
                    startActivityForResult(intent, 100)
                }
            }

            override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
                super.onActivityResult(requestCode, resultCode, data)
                if (requestCode == 100 && resultCode == RESULT_OK) {
                    val photo = data?.extras?.get("data") as Bitmap
                    val imageView = findViewById(R.id.imageView)
                    imageView.setImageBitmap(photo)
                }
            }
        }
        

Output: The app will open the camera, and the taken photo will be displayed in the ImageView.

Task Reminder with Notifications

        // MainActivity.kt
        package com.example.reminderapp

        import android.app.NotificationChannel
        import android.app.NotificationManager
        import android.content.Context
        import android.os.Build
        import android.os.Bundle
        import android.widget.Button
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity
        import androidx.core.app.NotificationCompat

        class MainActivity : AppCompatActivity() {

            private val CHANNEL_ID = "reminder_channel"

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

                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                    val name = "Reminder Channel"
                    val descriptionText = "Channel for task reminders"
                    val importance = NotificationManager.IMPORTANCE_DEFAULT
                    val channel = NotificationChannel(CHANNEL_ID, name, importance).apply {
                        description = descriptionText
                    }
                    val notificationManager: NotificationManager =
                        getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
                    notificationManager.createNotificationChannel(channel)
                }

                val notifyButton = findViewById<Button>(R.id.notifyButton)
                notifyButton.setOnClickListener {
                    val builder = NotificationCompat.Builder(this, CHANNEL_ID)
                        .setSmallIcon(R.drawable.ic_notification)
                        .setContentTitle("Task Reminder")
                        .setContentText("Don't forget to complete your task!")
                        .setPriority(NotificationCompat.PRIORITY_DEFAULT)

                    with(NotificationManagerCompat.from(this)) {
                        notify(1, builder.build())
                    }

                    Toast.makeText(this, "Reminder set!", Toast.LENGTH_SHORT).show()
                }
            }
        }
        

Output: A task reminder notification will be shown when the button is clicked.

Simple Audio Player

        // MainActivity.kt
        package com.example.audioplayer

        import android.media.MediaPlayer
        import android.os.Bundle
        import android.widget.Button
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

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

                val playButton = findViewById<Button>(R.id.playButton)
                val mediaPlayer = MediaPlayer.create(this, R.raw.sample_audio)

                playButton.setOnClickListener {
                    mediaPlayer.start()
                }
            }
        }
        

Output: When the play button is clicked, an audio file will be played.

Basic Todo List with Firebase Authentication

        // MainActivity.kt
        package com.example.todolist

        import android.os.Bundle
        import android.widget.Button
        import android.widget.EditText
        import android.widget.ListView
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity
        import com.google.firebase.auth.FirebaseAuth
        import com.google.firebase.database.DatabaseReference
        import com.google.firebase.database.FirebaseDatabase

        class MainActivity : AppCompatActivity() {

            private lateinit var auth: FirebaseAuth
            private lateinit var todoListView: ListView
            private lateinit var addButton: Button
            private lateinit var todoEditText: EditText
            private lateinit var database: DatabaseReference

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

                auth = FirebaseAuth.getInstance()  // Initialize Firebase Auth
                database = FirebaseDatabase.getInstance().reference  // Get a reference to the Firebase database

                todoListView = findViewById(R.id.todoListView)  // Find the ListView to display todos
                addButton = findViewById(R.id.addButton)  // Find the button to add a new todo
                todoEditText = findViewById(R.id.todoEditText)  // Find the EditText for user input

                addButton.setOnClickListener {
                    val todo = todoEditText.text.toString()  // Get the entered todo item text
                    if (todo.isNotEmpty()) {
                        val userId = auth.currentUser?.uid  // Get the current user's ID
                        val todoId = database.push().key  // Generate a unique key for the new todo item
                        if (todoId != null && userId != null) {
                            database.child("todos").child(userId).child(todoId).setValue(todo)  // Add the todo to the Firebase database
                            Toast.makeText(this, "Todo Added", Toast.LENGTH_SHORT).show()  // Show confirmation message
                        }
                    }
                }
            }
        }
        

Output: A basic todo list where users can add items, with Firebase Authentication for user-specific data.

Flashcards App for Learning

        // MainActivity.kt
        package com.example.flashcards

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

        class MainActivity : AppCompatActivity() {

            private val flashcards = listOf(
                "What is the capital of France?" to "Paris",
                "What is 2 + 2?" to "4",
                "Who wrote '1984'?" to "George Orwell"
            )

            private var currentCardIndex = 0  // Track the current flashcard

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

                val questionTextView = findViewById(R.id.questionTextView)  // TextView for displaying question
                val answerTextView = findViewById(R.id.answerTextView)  // TextView for displaying answer
                val nextButton = findViewById<Button>(R.id.nextButton)  // Button to move to next flashcard

                nextButton.setOnClickListener {
                    val currentCard = flashcards[currentCardIndex]
                    questionTextView.text = currentCard.first  // Set the question text
                    answerTextView.text = currentCard.second  // Set the answer text
                    currentCardIndex = (currentCardIndex + 1) % flashcards.size  // Move to next card in the list
                }
            }
        }
        

Output: A flashcards app where users can cycle through questions and answers.

Simple Stopwatch with Pause/Reset Functions

        // MainActivity.kt
        package com.example.stopwatch

        import android.os.Bundle
        import android.os.SystemClock
        import android.widget.Button
        import android.widget.Chronometer
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

            private lateinit var chronometer: Chronometer  // Chronometer for displaying time
            private var isRunning = false  // Track if stopwatch is running
            private var elapsedTime = 0L  // Track elapsed time

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

                chronometer = findViewById(R.id.chronometer)  // Find the Chronometer

                val startPauseButton = findViewById<Button>(R.id.startPauseButton)  // Button to start/pause stopwatch
                val resetButton = findViewById<Button>(R.id.resetButton)  // Button to reset stopwatch

                startPauseButton.setOnClickListener {
                    if (isRunning) {
                        elapsedTime = SystemClock.elapsedRealtime() - chronometer.base  // Calculate elapsed time
                        chronometer.stop()  // Stop the stopwatch
                        startPauseButton.text = "Start"  // Change button text to "Start"
                    } else {
                        chronometer.base = SystemClock.elapsedRealtime() - elapsedTime  // Reset stopwatch base
                        chronometer.start()  // Start the stopwatch
                        startPauseButton.text = "Pause"  // Change button text to "Pause"
                    }
                    isRunning = !isRunning  // Toggle the stopwatch state
                }

                resetButton.setOnClickListener {
                    chronometer.base = SystemClock.elapsedRealtime()  // Reset the stopwatch base
                    elapsedTime = 0L  // Reset elapsed time
                    if (isRunning) {
                        startPauseButton.text = "Start"  // Change button text to "Start"
                    }
                    isRunning = false  // Stop the stopwatch
                }
            }
        }
        

Output: A simple stopwatch with functionality to start, pause, and reset the timer.

Text-to-Speech App

        // MainActivity.kt
        package com.example.texttospeech

        import android.os.Bundle
        import android.speech.tts.TextToSpeech
        import android.speech.tts.TextToSpeech.OnInitListener
        import android.widget.Button
        import androidx.appcompat.app.AppCompatActivity
        import java.util.*

        class MainActivity : AppCompatActivity() {

            private lateinit var textToSpeech: TextToSpeech  // TextToSpeech instance

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

                textToSpeech = TextToSpeech(this, OnInitListener { status ->
                    if (status == TextToSpeech.SUCCESS) {
                        textToSpeech.language = Locale.US  // Set language to English
                    }
                })

                val speakButton = findViewById<Button>(R.id.speakButton)  // Button to trigger speech
                speakButton.setOnClickListener {
                    val text = "Hello, welcome to the Text-to-Speech app!"
                    textToSpeech.speak(text, TextToSpeech.QUEUE_FLUSH, null, null)  // Speak the text aloud
                }
            }

            override fun onDestroy() {
                super.onDestroy()
                textToSpeech.shutdown()  // Shutdown TTS when activity is destroyed
            }
        }
        

Output: The app will speak the provided text when the button is pressed.

Simple Voting System App

        // MainActivity.kt
        package com.example.votingsystem

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

        class MainActivity : AppCompatActivity() {

            private var votes = 0  // Track number of votes

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

                val voteButton = findViewById<Button>(R.id.voteButton)  // Button to cast a vote
                val votesTextView = findViewById(R.id.votesTextView)  // TextView to display vote count

                voteButton.setOnClickListener {
                    votes++  // Increment the vote count
                    votesTextView.text = "Votes: $votes"  // Update the vote count display
                }
            }
        }
        

Output: The app allows users to vote and displays the current number of votes.

Voice Recorder App

        // MainActivity.kt
        package com.example.voicerecorder

        import android.Manifest
        import android.content.pm.PackageManager
        import android.os.Bundle
        import android.media.MediaRecorder
        import android.widget.Button
        import android.widget.Toast
        import androidx.appcompat.app.AppCompatActivity
        import androidx.core.app.ActivityCompat
        import androidx.core.content.ContextCompat

        class MainActivity : AppCompatActivity() {

            private lateinit var mediaRecorder: MediaRecorder
            private var isRecording = false  // Track if recording is in progress

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

                val recordButton = findViewById<Button>(R.id.recordButton)  // Button to start/stop recording

                recordButton.setOnClickListener {
                    if (isRecording) {
                        stopRecording()  // Stop recording
                        recordButton.text = "Start Recording"  // Change button text
                    } else {
                        startRecording()  // Start recording
                        recordButton.text = "Stop Recording"  // Change button text
                    }
                    isRecording = !isRecording  // Toggle recording state
                }

                if (ContextCompat.checkSelfPermission(this, Manifest.permission.RECORD_AUDIO) != PackageManager.PERMISSION_GRANTED) {
                    ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.RECORD_AUDIO), 1)  // Request audio permission
                }
            }

            private fun startRecording() {
                mediaRecorder = MediaRecorder()
                mediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC)  // Set audio source to microphone
                mediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4)  // Set output format to MPEG_4
                mediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC)  // Set audio encoder to AAC
                mediaRecorder.setOutputFile("audio_recording.mp4")  // Set output file location
                mediaRecorder.prepare()  // Prepare the recorder
                mediaRecorder.start()  // Start recording
            }

            private fun stopRecording() {
                mediaRecorder.stop()  // Stop the recording
                mediaRecorder.release()  // Release the recorder resources
                Toast.makeText(this, "Recording saved!", Toast.LENGTH_SHORT).show()  // Show recording saved message
            }
        }
        

Output: A voice recorder app that allows users to record and save audio files.

Basic Timer App with Custom Ringtone

        // MainActivity.kt
        package com.example.timerapp

        import android.media.Ringtone
        import android.media.RingtoneManager
        import android.os.Bundle
        import android.os.CountDownTimer
        import android.widget.Button
        import android.widget.TextView
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

            private lateinit var timer: CountDownTimer  // Timer instance
            private lateinit var ringtone: Ringtone  // Ringtone instance

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

                val timeTextView = findViewById(R.id.timeTextView)  // TextView to show remaining time
                val startButton = findViewById<Button>(R.id.startButton)  // Button to start the timer

                ringtone = RingtoneManager.getRingtone(this, RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION))  // Set default ringtone

                startButton.setOnClickListener {
                    timer = object : CountDownTimer(30000, 1000) {  // 30-second countdown timer
                        override fun onTick(millisUntilFinished: Long) {
                            timeTextView.text = "Time left: ${millisUntilFinished / 1000} seconds"  // Update time every second
                        }

                        override fun onFinish() {
                            timeTextView.text = "Time's up!"  // Display when time is up
                            ringtone.play()  // Play ringtone when time is up
                        }
                    }
                    timer.start()  // Start the countdown timer
                }
            }
        }
        

Output: A timer app that plays a custom ringtone when the time is up.

Image Slider App

        // MainActivity.kt
        package com.example.imageslider

        import android.os.Bundle
        import android.widget.ImageView
        import android.widget.Button
        import androidx.appcompat.app.AppCompatActivity

        class MainActivity : AppCompatActivity() {

            private val images = listOf(R.drawable.image1, R.drawable.image2, R.drawable.image3)  // List of images
            private var currentIndex = 0  // Track the current image index

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

                val imageView = findViewById(R.id.imageView)  // ImageView to display images
                val nextButton = findViewById<Button>(R.id.nextButton)  // Button to move to next image

                nextButton.setOnClickListener {
                    currentIndex = (currentIndex + 1) % images.size  // Cycle through images
                    imageView.setImageResource(images[currentIndex])  // Update image in ImageView
                }
            }
        }
        

Output: An image slider app that cycles through images when the button is clicked.

Basic Shopping Cart

        // MainActivity.kt
        package com.example.shoppingcart

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

        class MainActivity : AppCompatActivity() {

            private var cartTotal = 0.0  // Track the total price of items in the cart

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

                val totalTextView = findViewById(R.id.totalTextView)  // TextView to display cart total
                val addButton = findViewById<Button>(R.id.addButton)  // Button to add an item to the cart

                addButton.setOnClickListener {
                    cartTotal += 20.0  // Add the price of an item to the cart total
                    totalTextView.text = "Total: $$cartTotal"  // Update the cart total display
                }
            }
        }
        

Output: A shopping cart app where users can add items and view the total price.