CountDownTimer in Android

 <?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"
    android:orientation="vertical"
    tools:context=".MainActivity"
    tools:ignore="HardcodedText">

    <androidx.appcompat.widget.AppCompatTextView
        android:id="@+id/txtcounter"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="50sp"
        android:layout_marginTop="50dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

 </androidx.constraintlayout.widget.ConstraintLayout>

 import android.annotation.SuppressLint
 import android.os.Bundle
 import android.os.CountDownTimer
 import android.view.View
 import androidx.appcompat.app.AppCompatActivity
 import androidx.appcompat.widget.AppCompatButton
 import androidx.appcompat.widget.AppCompatTextView
 import java.text.DecimalFormat
 import java.text.NumberFormat


 class MainActivity : AppCompatActivity() {
     @SuppressLint("MissingInflatedId")
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)
         val txtcounter = findViewById<View>(R.id.txtcounter) as AppCompatTextView
         object : CountDownTimer(50000, 1000) {
             @SuppressLint("SetTextI18n")
             override fun onTick(millisUntilFinished: Long) {
                val f: NumberFormat = DecimalFormat("00")
                val hour = (millisUntilFinished / 3600000) % 24
                val min = (millisUntilFinished / 60000) % 60
                val sec = (millisUntilFinished / 1000) % 60
                txtcounter.setText(
                    (f.format(hour) + ":" + f.format(min)).toString() + ":" + f.format(
                        sec
                    )
                 )
             }

             override fun onFinish() {
                 txtcounter.setText("00:00:00")
             }
         }.start()

     }
 }