Alarm Manager Example

java

alarm-management

android-development

broadcast-receiver

byAlex Kataev·Sep 9, 2024

Schedule tasks in Android using AlarmManager with these steps:

Create Intent for the action to execute.
Encase it in a PendingIntent.
Access AlarmManager by context.getSystemService(Context.ALARM_SERVICE).
Schedule with set(), setRepeating() or setExact().

Setting a 10-second alarm:

Intent intent = new Intent(context, AlarmReceiver.class);
PendingIntent pIntent = PendingIntent.getBroadcast(context, 0, intent, 0);
AlarmManager alarmMgr = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
alarmMgr.set(AlarmManager.RTC_WAKEUP, System.currentTimeMillis() + 10000, pIntent);

Note: Android 6.0 and above should use setExactAndAllowWhileIdle() for precision during Doze Mode.

Creating a simple Alarm

Here's a simple alarm setup that triggers a broadcast:

Create a BroadcastReceiver to respond when alarm fires:

public class AlarmReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        // Place your task here. Maybe feed your virtual cat? 🐈
    }
}

<receiver android:name=".AlarmReceiver" />

Set up the alarm using the Fast Setup instructions above.

Advanced Alarm Setup

The created alarm is great but it vanishes after a device reboot. For a more persistent alarm setup:

Create a Boot receiver: This resets the alarms after the device reboots.

public class BootCompletedReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        if (Intent.ACTION_BOOT_COMPLETED.equals(intent.getAction())) {
            // Alarm reset goes here
            // It's the phoenix of alarm world 🐦🔥
        }
    }
}

<receiver android:name=".BootCompletedReceiver">
    <intent-filter>
        <action android:name="android.intent.action.BOOT_COMPLETED"/>
    </intent-filter>
</receiver>

Permissions: Your app needs explicit permissions for using wake locks. Add these in your Manifest.xml:

<uses-permission android:name="android.permission.SET_ALARM"/>
<uses-permission android:name="android.permission.WAKE_LOCK"/>

Advanced Alarm Handling

Wake lock with BroadcastReceiver: Ensure tasks run when alarm fires by keeping the CPU running:

public class AlarmReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        PowerManager powerManager = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
        PowerManager.WakeLock wakeLock = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, 
        "MyApp:WakelockTag");
        wakeLock.acquire(10000); // You have 10 seconds to make coffee! ☕
        // Execute task
        wakeLock.release();
    }
}

IntentService and AlarmManager combo: For tasks that run a long time, use IntentService with AlarmManager:

public class AlarmService extends IntentService {
    public AlarmService() {
        super("AlarmService");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        // Here's a place for your long running task.
        // Like downloading the entire internet perhaps? 🌐
    }
}

Managing multiple alarms: Ensure unique PendingIntent request codes and use custom Intent action strings:

Intent i1 = new Intent(this, AlarmReceiver.class);
i1.setAction("com.myapp.ALARM_ONE");
PendingIntent alarm1PendingIntent = PendingIntent.getBroadcast(this, 0, i1, 0);

Intent i2 = new Intent(this, AlarmReceiver.class);
i2.setAction("com.myapp.ALARM_TWO");
PendingIntent alarm2PendingIntent = PendingIntent.getBroadcast(this, 1, i2, 0);

AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
alarmManager.set(AlarmManager.RTC_WAKEUP, timeForAlarm1, alarm1PendingIntent);
alarmManager.set(AlarmManager.RTC_WAKEUP, timeForAlarm2, alarm2PendingIntent);

Critical Tips for Alarm Management

Doze Mode awareness for newer Android versions.
Use SystemClock.elapsedRealtime() to schedule inexact repeating alarms that don't need to wake the device up.
Be mindful of the impact of frequent alarms on battery life and user experience.