Android tutorial (multipart)

This tutorial will cover AsyncTask, SQLite, SQLiteOpenHelper, ContentProvider, AlarmManager, BroadcastReceiver, custom filterable CursorAdapter, ListView, TextWatcher, JSONArray and JSONObject.
We will actually use HttpClient but I was talking about it already. Goal of tutorial is to fetch periodically search results from Twitter, store them in DB and display them in list view. We will make those search results searchable.

Cron job Android style

Android is Linux but Cron daemon is missing, we must use  AlarmManager and  BroadcastReceiver. Simplest form of  BroadcastReceiver looks like this:

public class CronJobScheduler extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        System.out.println("inside onReceive");
    }
}

To use it from your Activity you will do something like this:

Context context = getBaseContext();
AlarmManager manager=(AlarmManager)context.getSystemService(Context.ALARM_SERVICE);
Intent intent = new Intent(context, CronJobScheduler.class);
PendingIntent pending = PendingIntent.getBroadcast(context, 0, intent, 0);
manager.setRepeating(AlarmManager.RTC_WAKEUP, System.currentTimeMillis(), 1000 * 20 , pending);

and at appropriate place you will also stop scheduled job, like this:

Context context = getBaseContext();
Intent intent = new Intent(context, CronJobScheduler.class);
PendingIntent pending = PendingIntent.getBroadcast(context, 0, intent, 0);
AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
alarmManager.cancel(pending);

But that is not all, in AndroidManifest.xml we must place this:



It must be within application element. If we build app and run it in emulator it will print every 20 seconds inside onReceive.
In order to do something useful (like download JSON, parse it and insert data in DB) we will use later this code:

PowerManager manager = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
PowerManager.WakeLock lock = manager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "HOWZIT:)");
lock.acquire();
cr = context.getContentResolver();
new FetchItemsTask().execute();
lock.release();

In order to have this executed we will need to add some permissions to  AndroidManifest.xml, like this:



We are acquiring PowerManager.PARTIAL_WAKE_LOCK and that is CPU lock, we want CPU to be awake so that scheduled work could be done. As usual it is good idea to release CPU lock when work is done ;-)
If anybody needs code for this it is available here git://github.com/FBulovic/grumpyoldprogrammer.git there is few other things, also.
Next part of this tutorial will follow, soon.