Part 1 – Countdown Timer

[embedyt] https://www.youtube.com/watch?v=MDuGwI6P-X8[/embedyt]

In this tutorial we will learn, how to build a simple countdown timer, which shows the remaining time in minutes and seconds. It will have a start/pause button and a reset button which is only visible, if the timer is not running. For this, we will use the CountDownTimer interface and override the onTick and onFinish methods. We will set it’s time in milliseconds and format those milliseconds to minutes and seconds using the String.format method.

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activity_main.xmlMainActivity.java

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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="com.codinginflow.countdowntimerexample.MainActivity">

    <TextView
        android:id="@+id/text_view_countdown"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="00:00"
        android:textColor="@android:color/black"
        android:textSize="60sp" />

    <Button
        android:id="@+id/button_start_pause"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/text_view_countdown"
        android:layout_centerHorizontal="true"
        android:text="start" />

    <Button
        android:id="@+id/button_reset"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/text_view_countdown"
        android:layout_marginStart="11dp"
        android:layout_toEndOf="@+id/button_start_pause"
        android:text="reset"
        android:visibility="invisible"
        tools:visibility="visible" />

</RelativeLayout>

package com.codinginflow.countdowntimerexample;

import android.os.CountDownTimer;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.util.Locale;

public class MainActivity extends AppCompatActivity {
    private static final long START_TIME_IN_MILLIS = 600000;

    private TextView mTextViewCountDown;
    private Button mButtonStartPause;
    private Button mButtonReset;

    private CountDownTimer mCountDownTimer;

    private boolean mTimerRunning;

    private long mTimeLeftInMillis = START_TIME_IN_MILLIS;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mTextViewCountDown = findViewById(R.id.text_view_countdown);

        mButtonStartPause = findViewById(R.id.button_start_pause);
        mButtonReset = findViewById(R.id.button_reset);

        mButtonStartPause.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (mTimerRunning) {
                    pauseTimer();
                } else {
                    startTimer();
                }
            }
        });

        mButtonReset.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                resetTimer();
            }
        });

        updateCountDownText();
    }

    private void startTimer() {
        mCountDownTimer = new CountDownTimer(mTimeLeftInMillis, 1000) {
            @Override
            public void onTick(long millisUntilFinished) {
                mTimeLeftInMillis = millisUntilFinished;
                updateCountDownText();
            }

            @Override
            public void onFinish() {
                mTimerRunning = false;
                mButtonStartPause.setText("Start");
                mButtonStartPause.setVisibility(View.INVISIBLE);
                mButtonReset.setVisibility(View.VISIBLE);
            }
        }.start();

        mTimerRunning = true;
        mButtonStartPause.setText("pause");
        mButtonReset.setVisibility(View.INVISIBLE);
    }

    private void pauseTimer() {
        mCountDownTimer.cancel();
        mTimerRunning = false;
        mButtonStartPause.setText("Start");
        mButtonReset.setVisibility(View.VISIBLE);
    }

    private void resetTimer() {
        mTimeLeftInMillis = START_TIME_IN_MILLIS;
        updateCountDownText();
        mButtonReset.setVisibility(View.INVISIBLE);
        mButtonStartPause.setVisibility(View.VISIBLE);
    }

    private void updateCountDownText() {
        int minutes = (int) (mTimeLeftInMillis / 1000) / 60;
        int seconds = (int) (mTimeLeftInMillis / 1000) % 60;

        String timeLeftFormatted = String.format(Locale.getDefault(), "%02d:%02d", minutes, seconds);

        mTextViewCountDown.setText(timeLeftFormatted);
    }
}