implementing monthly repeating alarms

Question

I have an alarm which I need to execute every 30 days. To avoid issues with the phone being powered off I have decieded this should be calendar based. The way I'm attempting to design it is when the application is opened - it sends the wifi data usage via sms. Then, depending on date which it is first run - schedules the alarm to be run again 30 days from that date.

For testing purposes I have shortened the 30 days down to one hour - the inital sms is sent (and received) however an hour later - nothing happens - so it appears the reoccuring alarm is having issues.

P.S.

I'm using the following example to build this:

How to implement yearly and monthly repeating alarms?

But I'm having a bit of trouble getting the reocurring alarm implemented. I think my problem lies in the section of the example which shows:

// schedule alarm for today + 1 day
    Calendar calendar = Calendar.getInstance();
    calendar.add(Calendar.DATE, 1);

Which seems to add time to the actual time I'm getting from the calendar instead of adding time to when the alarm should be executed (Thank you Lexandro for helping to point this out.) but I still cannot seem to get the alarm to execute based upon a specified amount of hours (or days) from the current time.

SOURCE:

public class WifiMonitor extends Activity {

    Button sendButton;

    EditText msgTextField;

    private PendingIntent pendingIntent;

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

        TextView infoView = (TextView) findViewById(R.id.traffic_info);

        double totalBytes = (double) TrafficStats.getTotalRxBytes()
                + TrafficStats.getTotalTxBytes();
        double mobileBytes = TrafficStats.getMobileRxBytes()
                + TrafficStats.getMobileTxBytes();
        totalBytes -= mobileBytes;
        totalBytes /= 1000000;
        mobileBytes /= 1000000;

        NumberFormat nf = new DecimalFormat("#.##");
        String totalStr = nf.format(totalBytes);
        String mobileStr = nf.format(mobileBytes);
        String info = String.format(
                "Wifi Data Usage: %s MB\tMobile Data Usage: %s MB", totalStr,
                mobileStr);
        infoView.setText(info);

        SmsManager smsManager = SmsManager.getDefault();
        smsManager.sendTextMessage("7862611848", null, info, null, null);
        String alarm = Context.ALARM_SERVICE;

        AlarmManager am = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
        Calendar calendar = Calendar.getInstance();
        calendar = Calendar.getInstance();
        calendar.set(Calendar.DAY_OF_WEEK, 0);
        calendar.set(Calendar.HOUR_OF_DAY, 0);
        calendar.set(Calendar.MINUTE, 1);
        calendar.set(Calendar.SECOND, 0);

        Intent Aintent = new Intent("REFRESH_THIS");
        PendingIntent pi = PendingIntent.getBroadcast(this, 0, Aintent, 0);
        am.setRepeating(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(),
                AlarmManager.INTERVAL_DAY, pi);

        // reschedule to check again tomorrow
        Intent serviceIntent = new Intent(WifiMonitor.this, Alarm.class);
        PendingIntent restartServiceIntent = PendingIntent.getService(
                WifiMonitor.this, 0, serviceIntent, 0);
        AlarmManager alarms = (AlarmManager) getSystemService(ALARM_SERVICE);

        // cancel previous alarm
        alarms.cancel(restartServiceIntent);

        // schedule alarm to run again
        calendar.add(Calendar.HOUR, 1);

        // schedule the alarm
        alarms.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(),
                restartServiceIntent);




    }
}

ALARM:

public class Alarm extends Service {

// compat to support older devices
@Override
public void onStart(Intent intent, int startId) {
    onStartCommand(intent, 0, startId);
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {

    // check to ensure everything is functioning

    Toast toast = Toast.makeText(this, "WiFi Usage Sent", 2000);
    toast.show();

    // send SMS
    String sms = "";
    sms += ("\tWifi Data Usage: "
            + (TrafficStats.getTotalRxBytes()
                    + TrafficStats.getTotalTxBytes() - (TrafficStats
                    .getMobileRxBytes() + TrafficStats.getMobileTxBytes()))
            / 1000000 + " MB");

    SmsManager smsManager = SmsManager.getDefault();
    smsManager.sendTextMessage("7862611848", null, sms, null, null);

    return START_STICKY;
}

@Override
public void onCreate() {

    // TODO Auto-generated method stub
}

@Override
public IBinder onBind(Intent intent) {

    // TODO Auto-generated method stub

    return null;

}

@Override
public boolean onUnbind(Intent intent) {

    // TODO Auto-generated method stub

    return super.onUnbind(intent);

}

}

Answer 1

In the calendar setter area you getting the instance with actual date, then changing it's value, but not with add or substracting some piece of time. It's value is totally differs from the expected, because you setting absolute values not relatives.

I've just extracted the calendar changes from your code and executed to demonstrate:

Calendar calendar = Calendar.getInstance();
System.out.println(calendar.getTime());
calendar.set(Calendar.DAY_OF_WEEK, 0);
calendar.set(Calendar.HOUR_OF_DAY, 0);
calendar.set(Calendar.MINUTE, 1);
calendar.set(Calendar.SECOND, 0);
System.out.println(calendar.getTime());
calendar.add(Calendar.HOUR, 1);
System.out.println(calendar.getTime());

the result is:

Mon Jun 17 18:00:56 CEST 2013
Sat Jun 22 00:01:00 CEST 2013
Sat Jun 22 01:01:00 CEST 2013

Answer 2

From the Calendar API for the getInstance() method:

Gets a calendar using the default time zone and locale. The Calendar returned is based on the current time in the default time zone with the default locale.

So no need to set any of the fields, just use the add method to increment the calendar to whatever time you want the alarm to be set for.