CountDownTimer in Android using Kotlin

CountDownTimer app is about setting a time that moves in reverse order as it shows the time left in the upcoming event. A CountDownTimer is an accurate timer that can be used for a website or blog to display the count down to any special event, such as a birthday or anniversary. Likewise, here let’s create an Android App to learn how to create a simple Countdown App. So let’s begin app creation step by step towards its completion.

Step by Step Implementation

Step 1: Create a New Project

To create a new project in Android Studio please refer to Create a new project in android studio in kotlin.

Step 2: Working with the activity_main.xml file

Navigate to the app > res > layout > activity_main.xml and add the below code to that file. Below is the code for the activity_main.xml file.

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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/gfg"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="GeeksforGeeks"
        android:textColor="#189C1E"
        android:textSize="22sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.134" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:background="?android:attr/detailsElementBackground"
        android:gravity="center_horizontal|center_vertical"
        android:text="TextView"
        android:textColor="#189C1E"
        android:textSize="36sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/gfg"
        app:layout_constraintVertical_bias="0.0" />

</androidx.constraintlayout.widget.ConstraintLayout>

Step 3: Working with the MainActivity.kt file

Go to the MainActivity.kt file and refer to the following code. Below is the code for the MainActivity.kt file. Comments are added inside the code to understand the code in more detail.

Kotlin

package com.ayush.myapplication

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

class MainActivity : AppCompatActivity() {
    lateinit var textView : TextView
    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        textView = findViewById(R.id.textView)

        // time count down for 30 seconds,
        // with 1 second as countDown interval
        object : CountDownTimer(30000, 1000) {

            // Callback function, fired on regular interval
            override fun onTick(millisUntilFinished: Long) {
                textView.setText("seconds remaining: " + millisUntilFinished / 1000)
            }

            // Callback function, fired
            // when the time is up
            override fun onFinish() {
                textView.setText("done!")
            }
        }.start()
    }
}

The calls to onTick(long) are synchronized to this object so that one call to onTick(long) won’t ever occur before the previous callback is complete. So, our app is ready. And we can see the output.

Output: