I can see one possible issue, and it’s possible to do this without the workmanager (assuming the device has a healthy connection at the time the notification runs).

Instead of doing your network in the receiver itself, I suggest starting a service (foreground service if above Android 8.0), and doing your work there. This is because android’s time limit for a receiver is much lower than a service/foreground service. So to me, it sounds plausible that your receiver is killed before the network request completes, and so no notification is shown.

You can show the notification in the service, and also schedule the next alarm since setExactAndAllowWhileIdle isn’t a repetitive alarm on it’s own. So in your receiver, something like:

@Override
public void onReceive(Context context, Intent intent) {
        Intent service = new Intent(context, BirthdayNotifyService.class);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            context.startForegroundService(service);
        } else {
            context.startService(service);
        }
}

Then a possible service class:

public class BirthdayNotifyService extends IntentService {

    public BirthdayNotifyService() {
        super("BirthdayNotifyService");
    }

    @Override
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
        super.onStartCommand(intent, flags, startId);
        return START_STICKY;
    }

    @Override
    protected void onHandleIntent(@Nullable Intent intent) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            //Build a simple notification to show if a foreground service is neccesary
            Notification noti = notiBuilder.build();
            startForeground(1, noti);
        }

        //Do your network request work here. After completed, show your birthday notification and stop the foreground service.
    }
}

To stop the service, right AFTER you display your notification for birthdays, use the following:

stopForeground(true);
stopSelf();

UPDATE: I used this method on my phone (Xiaomi Redmi Note 8 plus), it worked a few times but then stopped working. It works perfectly fine on stock android, but not on all devices. Therefore I would still say this is not a reliable solution to send notification on specific times.

It seems like you are doing everything right, and as you said in the comments that it’s working on nexus S, I assume that you also declared the receiver in the manifest.

So after week of having the same problem here is the result:

In some devices with custom OS like Xiaomi, when you swipe the app away from the list of recents, the OS considers it as a force stop and therefor all services and other stuff will be killed. Based on Issue Tracker there is no way around it at the moment to solve this issue. They responded that they are working with OEMs to resolve this issue.

But based on my own experience, if you setup your notification using work manager, it will be delayed, but you will eventually receive it (at least most of the time).

But if you want the timing to be exact, there is no way to proceed at the moment.

The only solution at the moment is to give some permission manully at the moment. Please visit dontkillmyapp for more information regarding this manual settings.

I want to send offline notifications to users daily.Tried many things like: Alarm manager,Work manager but no luck.The notifications are not triggered or they just trigger at later.

Any way to get the job done?

Alarm function:

public void StartAlarm()
{
    Calendar calendar = Calendar.getInstance();
    calendar.setTimeInMillis(System.currentTimeMillis());
    calendar.set(Calendar.HOUR_OF_DAY,23);
    calendar.set(Calendar.MINUTE,59);
    calendar.set(Calendar.SECOND,0);


    AlarmManager alarmManager = (AlarmManager) getApplicationContext().getSystemService(Context.ALARM_SERVICE);


    Intent alarmIntent = new Intent(getApplicationContext(), AlarmReceiver.class);
    //alarmIntent.addFlags(Intent.FLAG_RECEIVER_FOREGROUND);

    Log.d("LOG", String.valueOf(calendar.getTimeInMillis()));

    PendingIntent pendingIntent = PendingIntent.getBroadcast(getApplicationContext(), 156, alarmIntent, 0);

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            alarmManager.setAndAllowWhileIdle(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.set(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pendingIntent);
        }

Work manager code:

 public MyWorker(@NonNull Context context, @NonNull WorkerParameters workerParams) {
    super(context, workerParams);
}


@NonNull
@Override
public Result doWork() {


    StartAlarm();


    Log.d("In worker","yes");


    return Result.success();
}

Work manager driver:

public void StartPeriodicWorker()
{

    final PeriodicWorkRequest periodicWorkRequest = new
            PeriodicWorkRequest.Builder(MyWorker.class,24,TimeUnit.HOURS)
            .addTag("Birthday")
            .build();

    WorkManager.getInstance(getApplicationContext()).enqueueUniquePeriodicWork("Birthday Notifier", ExistingPeriodicWorkPolicy.REPLACE, periodicWorkRequest);

}

Alarm Receiver:

  public class AlarmReceiver extends BroadcastReceiver {

private DatabaseReference myRef;
private ArrayList<String> allPeoples;

private int numberOfPeoples;

private Context ctx;

@Override
public void onReceive(Context context, Intent intent) {

    Toast.makeText(context,"In alarm receiver",Toast.LENGTH_LONG).show();

    ctx = context;
    initPeoples();

}

public String getCurrentDate() {
    Calendar calendar = Calendar.getInstance();
    SimpleDateFormat mdformat = new SimpleDateFormat("d MMMM");
    String strDate = mdformat.format(calendar.getTime());
    return strDate;
}


private  void initPeoples() {

    FirebaseDatabase database = FirebaseDatabase.getInstance();
    myRef = database.getReference("Users");
    myRef.keepSynced(true);

    myRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            allPeoples =  new ArrayList<>();
            for(DataSnapshot snapshot : dataSnapshot.getChildren()){
                if(snapshot.getKey().equals("Teacher") || snapshot.getKey().equals("Staff")){
                    for(DataSnapshot faculty : snapshot.child("peoples").getChildren()){
                        String birthday = (String) faculty.child("DOB").getValue();

                        if(birthday.equals(getCurrentDate())) {
                            String member = birthday;
                            allPeoples.add(member);
                        }
                    }
                }else{
                    for(DataSnapshot student : snapshot.child("peoples").getChildren()){
                        String birthday = (String) student.child("DOB").getValue();

                        if(birthday.equals(getCurrentDate())) {
                            String member = birthday;
                            allPeoples.add(member);
                        }
                    }
                }
            }

            numberOfPeoples = allPeoples.size();

            ShowNotification();

        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

}

public void ShowNotification()
{
    String CHANNEL_ID = "Channel_1453";
    String CHANNEL_NAME = "Birthday Notification";

    NotificationManagerCompat manager = NotificationManagerCompat.from(ctx);

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        NotificationChannel channel = new NotificationChannel(CHANNEL_ID, CHANNEL_NAME,
                NotificationManager.IMPORTANCE_HIGH);
        manager.createNotificationChannel(channel);
    }

    Notification notification = new NotificationCompat.Builder(ctx, CHANNEL_ID)
            .setSmallIcon(R.drawable.ic_stat_notify)
            .setContentTitle("Birthday Reminder")
            .setColor(Color.GREEN)
            .setContentText("Click to see who has birthday today!")
            .setPriority(NotificationCompat.PRIORITY_HIGH)
            .setAutoCancel(true)
            .setCategory(NotificationCompat.CATEGORY_MESSAGE)
            .setContentIntent(PendingIntent.getActivity(ctx, 0, new Intent(ctx, Birthday.class), PendingIntent.FLAG_UPDATE_CURRENT))
            .build();

    manager.notify(454, notification);
}

}