How to create a Stopwatch App using Android Studio

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp">

    <TextView
        android:id="@+id/time_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:textAppearance="@android:style/TextAppearance.Large"
        android:textSize="56sp" />

    <Button
        android:id="@+id/start_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="20dp"
        android:onClick="onClickStart"
        android:text="@string/start" />

    <Button
        android:id="@+id/stop_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="8dp"
        android:onClick="onClickStop"
        android:text="@string/stop" />

    <Button
        android:id="@+id/reset_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="8dp"
        android:onClick="onClickReset"
        android:text="@string/reset" />
 </LinearLayout>

 import android.annotation.SuppressLint
 import android.os.Bundle
 import android.view.View
 import android.widget.TextView
 import androidx.appcompat.app.AppCompatActivity
 import java.util.Locale


 class MainActivity : AppCompatActivity() {
     private var seconds = 0
     private var running = false
     private var wasRunning = false

    @SuppressLint("MissingInflatedId")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        if (savedInstanceState != null) {

            seconds= savedInstanceState
                .getInt("seconds")
            running= savedInstanceState
                .getBoolean("running")
            wasRunning= savedInstanceState
                .getBoolean("wasRunning")
        }
        runTimer()

    }

    private fun runTimer() {
        val timeView = findViewById<View>(
            R.id.time_view
        ) as TextView

        val handler
                : android.os.Handler = android.os.Handler()

        handler.post(object : Runnable {
            override fun run() {
                val hours = seconds / 3600
                val minutes = (seconds % 3600) / 60
                val secs = seconds % 60
                val time = String.format(
                    Locale.getDefault(),
                    "%d:%02d:%02d", hours,
                    minutes, secs
                )

                timeView.text = time
                if (running) {
                    seconds++
                }
                handler.postDelayed(this, 1000)
            }
        })
    }

    public override fun onSaveInstanceState(
        savedInstanceState: Bundle
    ) {
        super.onSaveInstanceState(savedInstanceState)
        savedInstanceState
            .putInt("seconds", seconds)
        savedInstanceState
            .putBoolean("running", running)
        savedInstanceState
            .putBoolean("wasRunning", wasRunning)
    }
    override fun onPause() {
        super.onPause()
        wasRunning = running
        running = false
    }
    override fun onResume() {
        super.onResume()
        if (wasRunning) {
            running = true
        }
    }
    fun onClickStart(view: View?) {
        running = true
    }
    fun onClickStop(view: View?) {
        running = false
    }
    fun onClickReset(view: View?) {
       running = false
        seconds = 0
     }
 }