AlarmManager: how to schedule a daily alarm and deal with time changes

AlarmManager: Scheduling Daily Alarms and Handling Time Changes

AlarmManager is a powerful Android system service for scheduling tasks at specific times or intervals. It’s commonly used for recurring events like daily reminders, background updates, or scheduled jobs. This article explores how to schedule a daily alarm with AlarmManager, including the complexities of handling time changes.

Setting Up a Daily Alarm

1. Requesting Alarm Permissions

To use AlarmManager, you need to request the necessary permissions in your app’s manifest file:

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

2. Defining the Alarm Intent

You’ll need to create an Intent that will be triggered when the alarm fires.

Intent intent = new Intent(context, AlarmReceiver.class);
PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

Here:

• AlarmReceiver is a BroadcastReceiver class that handles the alarm action.
• PendingIntent is a wrapper for the Intent, enabling you to trigger the alarm.
• FLAG_UPDATE_CURRENT ensures that any existing PendingIntent with the same request code is replaced.

3. Scheduling the Alarm

Utilize AlarmManager to set the alarm at the desired time:

AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.HOUR_OF_DAY, 8); // Set alarm at 8:00 AM
calendar.set(Calendar.MINUTE, 0);
calendar.set(Calendar.SECOND, 0);

alarmManager.setRepeating(
    AlarmManager.RTC_WAKEUP,
    calendar.getTimeInMillis(),
    AlarmManager.INTERVAL_DAY,
    pendingIntent);

Explanation:

• RTC_WAKEUP ensures the device wakes up to trigger the alarm.
• calendar.getTimeInMillis() provides the initial trigger time.
• AlarmManager.INTERVAL_DAY sets the alarm to repeat daily.

Handling Time Changes

Time changes, like daylight saving time (DST), can pose challenges. Consider these approaches:

1. Using AlarmManager.RTC_WAKEUP

As illustrated above, RTC_WAKEUP is the recommended approach as it allows for accurate time scheduling, even when time changes occur.

2. Using Calendar.getInstance()

Ensure you use Calendar.getInstance() within your AlarmReceiver to get the accurate current time, taking into account any time zone shifts.

3. Handling Device Restart

After a device restart, alarms might not be scheduled automatically. To address this:

@Override
public void onReceive(Context context, Intent intent) {
  if (intent.getAction().equals(Intent.ACTION_BOOT_COMPLETED)) {
    // Reschedule your alarm here
  }
}

Code Example: Daily Alarm with Time Change Handling

package com.example.your_app_name;

import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Build;
import android.util.Log;

import java.util.Calendar;

public class AlarmReceiver extends BroadcastReceiver {

  private static final String TAG = "AlarmReceiver";

  @Override
  public void onReceive(Context context, Intent intent) {
    if (intent.getAction().equals(Intent.ACTION_BOOT_COMPLETED)) {
      scheduleDailyAlarm(context);
    } else {
      // Handle your alarm actions here, like showing a notification
      Log.d(TAG, "Alarm fired!");
    }
  }

  private void scheduleDailyAlarm(Context context) {
    AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
    Intent alarmIntent = new Intent(context, AlarmReceiver.class);
    PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, alarmIntent, PendingIntent.FLAG_UPDATE_CURRENT);

    Calendar calendar = Calendar.getInstance();
    calendar.set(Calendar.HOUR_OF_DAY, 8); // Set alarm at 8:00 AM
    calendar.set(Calendar.MINUTE, 0);
    calendar.set(Calendar.SECOND, 0);

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
      alarmManager.setExactAndAllowWhileIdle(
          AlarmManager.RTC_WAKEUP,
          calendar.getTimeInMillis(),
          pendingIntent);
    } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT) {
      alarmManager.setExact(
          AlarmManager.RTC_WAKEUP,
          calendar.getTimeInMillis(),
          pendingIntent);
    } else {
      alarmManager.setRepeating(
          AlarmManager.RTC_WAKEUP,
          calendar.getTimeInMillis(),
          AlarmManager.INTERVAL_DAY,
          pendingIntent);
    }
  }
}

Conclusion

AlarmManager empowers you to schedule recurring tasks efficiently on Android. By using AlarmManager.RTC_WAKEUP and handling time changes appropriately, you can ensure your daily alarms remain accurate and reliable even when time zones adjust.