Creating And Scheduling Alarms Using AlarmManager In Android

Introduction

According to Google's Android Doc, "Alarms (based on the AlarmManager class) give you a way to perform time-based operations outside the lifetime of your application".

An example can be thought of as downloading the weather report once in a day or twice in a day and notifying the user.

Characteristics of Alarms:

• Alarms can let one to fire Intents at set times or in certain time intervals.
• Alarms can be used together with the broadcast receiver to notifies user.
• Alarms can triggers even if device falls asleep because they run outside the application.
• Alarms can be scheduled to an specific sharp time thus reducing system resources by not relaying on background services.

Choosing an Alarm Type

• ELAPSED_REALTIME
  
  Elapsed Time means time including the sleep time fromwhen the device gets booted. It doesn't wake up the device.
  
  
• ELAPSED_REALTIME_WAKEUP 
  
  In ELAPSED_REALTIME_WAKEUP it wakes up the and fires the pending intent after the specified interval of time has elapsed since device has booted.

• RTC
  
  In this case pending intent fired at the specified time but does not wake up the device.

• RTC_WAKEUP
  
  In this case alarms wakes up the device to fire the pending intent at the specified time.

Starting Alarm at Particular Time

There are many scenarios in which we have to set alarm and notify user at sharp time. So let's have a look to this specific code given below. This piece of code runs as it notifies (vibrate in our case) user at the time mentioned like 14 hrs and at 40 min but it is up to you which time you would prefer.

You might set time at 15 hrs or any time. We are using method setInexactRepeating() because repeating the alarm at hourly intervals you can set interval at two hours and might do a half day or full day(INTERVAL_DAY). We are using the AlarmManager.RTC_WAKEUP because if device is sleeping then it will wake it up.

public void startAlertAtParticularTime() {

        // alarm first vibrate at 14 hrs and 40 min and repeat itself at ONE_HOUR interval

        intent = new Intent(this, MyBroadcastReceiver.class);
        pendingIntent = PendingIntent.getBroadcast(
                this.getApplicationContext(), 280192, intent, PendingIntent.FLAG_CANCEL_CURRENT);

        Calendar calendar = Calendar.getInstance();
        calendar.setTimeInMillis(System.currentTimeMillis());
        calendar.set(Calendar.HOUR_OF_DAY, 14);
        calendar.set(Calendar.MINUTE, 40);

        alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);

        alarmManager.setInexactRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(),
                AlarmManager.INTERVAL_HOUR, pendingIntent);

        Toast.makeText(this, "Alarm will vibrate at time specified",
                Toast.LENGTH_SHORT).show();

    }

The above part of code is just to show how to fire the intent at a particular time now we will see the entire code of MainActivity.java and in this case we will set alarms by the time provided by user in seconds and thereafter repeat it every 10 seconds.

package com.example.gkumar.alarmwithbroadcastreceiver;

import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.util.Calendar;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    Button alarmbutton, cancelButton;
    EditText text;
    PendingIntent pendingIntent;
    AlarmManager alarmManager;
    Intent intent;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        alarmbutton = (Button) findViewById(R.id.button);
        cancelButton = (Button) findViewById(R.id.button2);
        text = (EditText) findViewById(R.id.editText);
        alarmbutton.setOnClickListener(this);
        cancelButton.setOnClickListener(this);

        /* use this method if you want to start Alarm at particular time*/

           // startAlertAtParticularTime();

    }

    // This method to be called at Start button click and set repeating at every 10 seconds interval

    public void startAlert(View view) {
        if (!text.getText().toString().equals("")) {
            int i = Integer.parseInt(text.getText().toString());
            intent = new Intent(this, MyBroadcastReceiver.class);
            pendingIntent = PendingIntent.getBroadcast(
                    this.getApplicationContext(), 280192, intent, PendingIntent.FLAG_CANCEL_CURRENT);
            alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);
            alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, Calendar.getInstance().getTimeInMillis() + (i * 1000), 10000
                    , pendingIntent);

            Toast.makeText(this, "Alarm will set in " + i + " seconds",
                    Toast.LENGTH_LONG).show();
        }else {
            Toast.makeText(this,"Please Provide time ",Toast.LENGTH_SHORT).show();
        }

    }

    public void startAlertAtParticularTime() {

        // alarm first vibrate at 14 hrs and 40 min and repeat itself at ONE_HOUR interval

        intent = new Intent(this, MyBroadcastReceiver.class);
        pendingIntent = PendingIntent.getBroadcast(
                this.getApplicationContext(), 280192, intent, PendingIntent.FLAG_CANCEL_CURRENT);

        Calendar calendar = Calendar.getInstance();
        calendar.setTimeInMillis(System.currentTimeMillis());
        calendar.set(Calendar.HOUR_OF_DAY, 14);
        calendar.set(Calendar.MINUTE, 40);

        alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);

        alarmManager.setInexactRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(),
                AlarmManager.INTERVAL_HOUR, pendingIntent);

        Toast.makeText(this, "Alarm will vibrate at time specified",
                Toast.LENGTH_SHORT).show();

    }

    @Override
    public void onClick(View v) {
        if (v.getId() == R.id.button) {
            startAlert(v);
        } else {
            if (alarmManager != null) {

                alarmManager.cancel(pendingIntent);
                Toast.makeText(this, "Alarm Disabled !!",Toast.LENGTH_LONG).show();

            }

        }
    }

    @Override
    protected void onStop() {
        super.onStop();
        if (alarmManager != null) {
            alarmManager.cancel(pendingIntent);
        }


    }
}

Now its time to look around corresponding UI part given below as activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.gkumar.alarmwithbroadcastreceiver.MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="start alarm"
        android:id="@+id/button"
        android:layout_below="@+id/editText"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="35dp" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:inputType="phone"
        android:hint="Provide Time In Seconds Only"
        android:id="@+id/editText"
        android:gravity="center"
        android:layout_marginTop="50dp"
        android:layout_below="@+id/textView"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Please Enter Time To Set an Alarm"
        android:id="@+id/textView"
        android:textSize="20sp"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true" />

    <Button

        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Stop Alarm"
        android:id="@+id/button2"
        android:layout_below="@+id/button"
        android:layout_alignLeft="@+id/button"
        android:layout_alignStart="@+id/button"
        android:layout_marginTop="33dp" />

</RelativeLayout>

Coding the Manifest file and adding permission to vibrate and registering the receiver of name MyBroadcastReceiver as shown in figure.



Now After Registering a BroadcastReciever that notifies the userwhether it means vibrate or executing the alarm as shown in code below.

package com.example.gkumar.alarmwithbroadcastreceiver;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Vibrator;
import android.widget.Toast;

public class MyBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "Time Up... Now Vibrating !!!",
                Toast.LENGTH_LONG).show();
        Vibrator vibrator = (Vibrator) context
                .getSystemService(Context.VIBRATOR_SERVICE);
        vibrator.vibrate(2000);
    }
}

Running the Application

Starting state

When application runs the first time you will see this image and click on Start Alarm button.



Scheduling the Alarm

Please enter the time you want to start alarm that is if you entered five say 5 then it will schedule by five seconds.



Alarm Started 

In this case alarm starts functioning and vibrating starts and now it repeats after 10 seconds and so on.



Stopping Alarm

After clicking on the Stop button Alarm gets cancelled and stops functioning



Summary

In this article we has learned how to create and schedule the alarms and notify user via BroadcastReceiver. Selecting first the Alarm type and appropriate methods to start Alarm using AlarmManager class.

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