Android Alarm Based On a Time Stored in Shared Preferences

Question

I'm building an android application which sends wifi usage data once a month via sms. Thus far I've managed to send the amount of wifi data usage via sms, save the date at which the application is first launched via shared preferences so it can be accessed later - now I need to find a method to cause the alarm to expire 30 days from the date I've saved via shared preferences. This shouldn't be too hard - except I need to check if it's been 30 days yet every time the device boots - to compensate for time the phone may have been off.

Can someone help me accomplish this?

SOURCE SNIPPET:

// get the current date Date date = new Date(System.currentTimeMillis());

        // convert the date to milliseconds
        long millis = date.getTime();

        // save the date to shared preferences

        SharedPreferences prefs = millis;
        SharedPreferences.Editor editor = PreferenceManager
                .getDefaultSharedPreferences(getApplicationContext());

        editor.putLong("time", date.getTime());
        editor.commit();

        // get the saved date

        Date myDate = new Date(prefs.getLong("time", 0));
    }

    // set the alarm to expire 30 days from the date stored in sharePreferences (this portion is not functional - and it is what I need help with) 


    public void invokeAlarm(long invokeTime, long rowId) {
        AlarmManager am = (AlarmManager) getSystemService(ALARM_SERVICE);
        Intent i = new Intent(this, Alarm.class);
        i.putExtra("rowId", String.valueOf(rowId));
        am.set(AlarmManager.RTC_WAKEUP, invokeTime, PendingIntent.getService(
                this, (int) System.currentTimeMillis(), i, 0));

FULL 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);

        // get 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);

        // send traffic info via sms
        SmsManager smsManager = SmsManager.getDefault();
        smsManager.sendTextMessage("7865555555", null, info, null, null);
        String alarm = Context.ALARM_SERVICE;

        // get the current date
        Date date = new Date(System.currentTimeMillis());

        // convert the date to milliseconds
        long millis = date.getTime();

        // save the date to shared preferences

        SharedPreferences prefs = millis;
        SharedPreferences.Editor editor = PreferenceManager
                .getDefaultSharedPreferences(getApplicationContext());

        editor.putLong("time", date.getTime());
        editor.commit();

        // get the saved date

        Date myDate = new Date(prefs.getLong("time", 0));
    }

    // set the alarm to expire 30 days from the date stored in sharePreferences (this portion is not functional - and it is what I need help with) 


    public void invokeAlarm(long invokeTime, long rowId) {
        AlarmManager am = (AlarmManager) getSystemService(ALARM_SERVICE);
        Intent i = new Intent(this, Alarm.class);
        i.putExtra("rowId", String.valueOf(rowId));
        am.set(AlarmManager.RTC_WAKEUP, invokeTime, PendingIntent.getService(
                this, (int) System.currentTimeMillis(), i, 0));
    }

}

UPDATED SOURCE AFTER FIRST RESPONSE:

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);

        // get 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);

        // send traffic info via sms
        SmsManager smsManager = SmsManager.getDefault();
        smsManager.sendTextMessage("7862611848", null, info, null, null);
        String alarm = Context.ALARM_SERVICE;

        // get the current date
        Date date = new Date(System.currentTimeMillis());

        // convert the date to milliseconds
        long millis = date.getTime();

        // save the date to shared preferences
        SharedPreferences prefs = PreferenceManager
                .getDefaultSharedPreferences(getApplicationContext());
        // SharedPreferences prefs = millis;
        // SharedPreferences.Editor editor = PreferenceManager
        // .getDefaultSharedPreferences(getApplicationContext());

        editor.putLong("time", date.getTime());
        editor.commit();

        // get the saved date

        Date myDate = new Date(prefs.getLong("time", 0));
    }

    // set the alarm to expire 30 days from the date stored in sharePreferences
    public void invokeAlarm(long invokeTime, long rowId) {
        AlarmManager am = (AlarmManager) getSystemService(ALARM_SERVICE);
        Intent i = new Intent(this, Alarm.class);
        i.putExtra("rowId", String.valueOf(rowId));
        am.set(AlarmManager.RTC_WAKEUP, invokeTime, PendingIntent.getService(
                this, (int) System.currentTimeMillis(), i, 0));

        Calendar cal = Calendar.getInstance();
        cal.setTime(myDate);
        cal.add(Calendar.DATE, 30);
        invokeAlarm(cal.getTimeInMillis(), rowId);
    }

}

Answer 1

You don't need to check how much time is elapsed. AlarmManager.RTC_WAKEUP is measured in real UTC time and is not relative to device up time.

So first your call to invokeAlarm should just use something like

Calendar cal = Calendar.getInstance();
cal.setTime(myDate);
cal.add(Calendar.DATE, 30);
invokeAlarm(cal.getTimeInMillis(), rowId);

Just a note that the AlarmManager loses all alarms on reboot. You need to set up a Service that is a Broadcast Receiver for the "Intent.ACTION_BOOT_COMPLETED" intent.

In this service just set the alarm again using the same logic.