MainActivity.kt
package com.cfsuman.kotlintutorials
import android.app.Activity
import android.content.res.ColorStateList
import android.graphics.Color
import android.os.Bundle
import android.os.Handler
import android.os.Looper
import android.view.View
import android.widget.Button
import android.widget.ProgressBar
import android.widget.TextView
import androidx.constraintlayout.widget.ConstraintLayout
import androidx.transition.TransitionManager
import kotlin.random.Random
class MainActivity : Activity() {
    var progressStatus = 0
    var handler = Handler(Looper.getMainLooper())
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        // Get the widgets reference from XML layout
        val rootLayout = findViewById<ConstraintLayout>(R.id.rootLayout)
        val button = findViewById<Button>(R.id.button)
        val textView = findViewById<TextView>(R.id.textView)
        val progressBar = findViewById<ProgressBar>(R.id.progressBar)
        val progressBar2 = findViewById<ProgressBar>(R.id.progressBar2)
        val progressBar3 = findViewById<ProgressBar>(R.id.progressBar3)
        // change the indeterminate progress color programmatically
        progressBar3.indeterminateTintList = 
            ColorStateList.valueOf(Color.RED)
        // button click listener
        button.setOnClickListener {
            button.isEnabled = false
            TransitionManager.beginDelayedTransition(rootLayout)
            progressBar.visibility = View.VISIBLE
            progressBar2.visibility = View.VISIBLE
            progressBar3.visibility = View.VISIBLE
            // set up progress bar on initial stage
            progressBar.progress = 0
            progressStatus = 0
            // generate random number of files to download
            val filesToDownload= Random.nextInt(200,500)
            // set up max value for progress bar
            progressBar.max = filesToDownload
            Thread(Runnable {
                while (progressStatus < filesToDownload){
                    // update progress status
                    progressStatus +=1
                    // sleep the thread for 50 milliseconds
                    Thread.sleep(50)
                    // update the progress bar
                    handler.post {
                        // calculate the percentage
                        val percentage = ((progressStatus.toDouble()
                                / filesToDownload) * 100).toInt()
                        // update the text view
                        textView.text = "Downloaded $progressStatus of " +
                                "$filesToDownload files ($percentage%)"
                        if (progressStatus == filesToDownload){
                            button.isEnabled = true
                            TransitionManager
                                .beginDelayedTransition(rootLayout)
                            progressBar.visibility = View.INVISIBLE
                            progressBar2.visibility = View.INVISIBLE
                            progressBar3.visibility = View.INVISIBLE
                        }
                    }
                }
            }).start()
        }
    }
}
activity_main.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:id="@+id/rootLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="24dp"
    android:background="#DCDCDC">
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="24dp"
        android:padding="12dp"
        android:fontFamily="sans-serif"
        android:textSize="20sp"
        android:textStyle="bold"
        tools:text="TextView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
    <ProgressBar
        android:id="@+id/progressBar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="64dp"
        android:layout_marginTop="12dp"
        android:visibility="invisible"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />
    <ProgressBar
        android:id="@+id/progressBar2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:visibility="invisible"
        android:indeterminateTint="#0018A8"
        android:indeterminateTintMode="src_in"
        android:layout_marginStart="16dp"
        app:layout_constraintBottom_toBottomOf="@+id/progressBar"
        app:layout_constraintStart_toEndOf="@+id/progressBar" />
    <ProgressBar
        android:id="@+id/progressBar3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:visibility="invisible"
        android:layout_marginStart="16dp"
        app:layout_constraintBottom_toBottomOf="@+id/progressBar2"
        app:layout_constraintStart_toEndOf="@+id/progressBar2" />
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="Start Task"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/progressBar" />
</androidx.constraintlayout.widget.ConstraintLayout>