what approach should i follow to make Timer service in android

I am working on an interval timer which make an alarm every interval (E.g. 30mins). I want to make the timer work in background or when device is in sleep and show a notification, I was told to use Intent Service but its deprecated. what should i use? -I want to support until API 21

Answer

You need to create a BroadcastReceiver. For example, using AlarmManager:

int repeatTime = 30;  //Repeat alarm time in seconds
AlarmManager processTimer = (AlarmManager)getSystemService(ALARM_SERVICE);
Intent intent = new Intent(this, processTimerReceiver.class);   
PendingIntent pendingIntent = PendingIntent.getBroadcast(this, 0,  intent, 
PendingIntent.FLAG_UPDATE_CURRENT);
//Repeat alarm every second
processTimer.setRepeating(AlarmManager.RTC_WAKEUP, 
System.currentTimeMillis(),repeatTime*1000, pendingIntent); 

And create your processTimerReciever class:

//This is called every second (depends on repeatTime)
public class processTimerReceiver extends BroadcastReceiver{

    @Override
    public void onReceive(Context context, Intent intent) {
        //Do something every 30 seconds
    }
}

Remember to register into Manifest:

<receiver android:name="processTimer" >
   <intent-filter>
       <action android:name="processTimerReceiver" >
       </action>
   </intent-filter>
</receiver>

EDIT:

If your app use an internet connection, you can send every 30 mins a notification using Firebase