Android Kotlin: How to create a progress bar with percentage counter

This code snippet showcases how to implement a progress bar with a corresponding percentage counter in an Android application written in Kotlin. It simulates a file download scenario to demonstrate the progress functionality.

The code consists of two parts: the Kotlin class (MainActivity.kt) handling the logic and the layout file (activity_main.xml) defining the user interface elements.

Breakdown of the Code

The MainActivity.kt class manages the user interaction and progress updates:

Initialization: It retrieves references to the button, text view, and progress bar from the layout using findViewById. Additionally, a Handler object is created to update the UI thread from the background thread.
Button Click Listener: Clicking the button triggers the following actions:
- Disables the button to prevent multiple clicks.
- Initializes variables for progress status and the total number of files to download (randomly generated).
- Sets the maximum value of the progress bar based on the total files.
Background Thread: A new thread is created to simulate the download process. Inside the thread:
- A loop iterates until all files are downloaded (based on progressStatus).
- The progress is incremented, and the thread sleeps for a short duration (simulating download time).
- Using the Handler.post method, the UI thread is updated with:
  - The progress bar value set to the current progress.
  - The percentage calculated based on downloaded files and total files.
  - The text view updated with the download status.
- Once the download is complete (progress reaches the total files), the button is re-enabled.

The activity_main.xml defines the layout:

It uses a ConstraintLayout to position the UI elements.
It includes a TextView to display the download status.
It has a ProgressBar with a horizontal style to visualize the download progress.
Finally, a Button initiates the download process.

MainActivity.kt


package com.cfsuman.kotlintutorials

import android.app.Activity
import android.os.Bundle
import android.os.Handler
import android.os.Looper
import android.widget.Button
import android.widget.ProgressBar
import android.widget.TextView
import kotlin.random.Random


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


        // Get the widgets reference from XML layout
        val button = findViewById<Button>(R.id.button)
        val textView = findViewById<TextView>(R.id.textView)
        val progressBar = findViewById<ProgressBar>(R.id.progressBar)

        // Initialize a new Handler instance
        val handler = Handler(Looper.getMainLooper())


        // Set a click listener for button widget
        button.setOnClickListener{
            // Disable the button itself
            it.isEnabled = false

            // Variable to hold progress status
            var progressStatus = 0;

            // Set up progress bar on initial stage
            progressBar.progress = 0

            // Generate random number of files to download
            val filesToDownload= Random.nextInt(50,200)

            // set up max value for progress bar
            progressBar.max = filesToDownload


            // Start the lengthy operation in a background thread
            Thread {
                while (progressStatus < filesToDownload) {
                    // Update the progress status
                    progressStatus += 1

                    // Try to sleep the thread for 100 milliseconds
                    try {
                        Thread.sleep(100)
                    } catch (e: InterruptedException) {
                        e.printStackTrace()
                    }

                    handler.post {
                        // Update the progress bar
                        progressBar.progress = progressStatus

                        // Calculate the percentage
                        val percentage = ((progressStatus.toDouble()
                                / filesToDownload) * 100).toInt()

                        // Update the text view
                        textView.text = "Downloaded $progressStatus of " +
                                "$filesToDownload files ($percentage%)"

                        // When the task done
                        if (progressStatus == filesToDownload) {
                            // Enable the button
                            button.isEnabled = true
                        }
                    }
                }
            }.start() // Start the operation
        }
    }
}

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="36dp"
        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"
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="24dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />

    <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>