Android™ Application Development - Bahar Ali Khan

Chapter 8: Working in the Background
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Alarms provide a mechanism for fi ring Intents at set times, outside the control of your application life
cycle. You’ll learn to use Alarms to start Services, open Activities, or broadcast Intents based on either
the clock time or the time elapsed since device boot. An Alarm will fi re even after its owner application
has been closed, and can (if required) wake a device from sleep.
Introducing Services
Unlike Activities, which present a rich graphical interface to users, Services run in the background —
updating your Content Providers, fi ring Intents, and triggering Notifi cations. They are the perfect way
to perform regular processing or handle events even after your application’s Activities are invisible,
inactive, or have been closed.
With no visual interface, Services are started, stopped, and controlled from other application components
including other Services, Activities, and Broadcast Receivers. If your application regularly, or continuously,
performs actions that don’t depend directly on user input, Services may be the answer.
Started Services receive higher priority than inactive or invisible Activities, making them less likely to
be terminated by the run time’s resource management. The only time Android will stop a Service prematurely
is when it’s the only way for a foreground Activity to gain required resources; if that happens,
your Service will be restarted automatically when resources become available.
Applications that update regularly but only rarely or intermittently need user interaction are good candidates
for implementation as Services. MP3 players and sports-score monitors are examples of applications
that should continue to run and update without an interactive visual component (Activity) visible.
Further examples can be found within the software stack itself; Android implements several Services
including the Location Manager, Media Controller, and the Notifi cation Manager.
Creating and Controlling Services
Services are designed to run in the background, so they need to be started, stopped, and controlled by
other application components.
In the following sections, you’ll learn how to create a new Service, and how to start and stop it using
Intents and the startService method. Later you’ll learn how to bind a Service to an Activity, providing
a richer interface for interactivity.
Creating a Service
To defi ne a Service, create a new class that extends the Service base class. You’ll need to override
onBind and onCreate, as shown in the following skeleton class:
import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
public class MyService extends Service {
@Override
public void onCreate() {