This document discusses Android services and provides examples of creating different types of services. It explains that a service is an application component that can perform long-running operations in the background without a user interface. The document covers started services, which run indefinitely until stopped, and bound services, which run only as long as components are bound to them. It provides code examples for creating started services by extending the Service and IntentService classes and for creating a bound service using the Binder pattern.

1. SCHOOL OF ENGINEERING
Activities
1
CE701
Mobile Computing
Tejas Vasavada
Android Services

2. Following are outcomes of this lecture:
• Students will become aware of need of using
services.
• Students will understand service life cycle.
• Students will be able to create services on
their own.
Outcomes

3. • A Service is an application component that
can perform long-running operations in the
background.
• It does not provide a user interface.
• Some application component can start a
service. Service will continue to run in the
background even if the user switches to
different application.
Service

4. • Additionally, a component can bind to a
service to interact with it and even perform
interprocess communication (IPC).
• A service can essentially take two forms:
1) Started
2) Bound

5. Started Service

6. • A service is called "started“ service if an
application component (such as an activity)
starts it by calling startService( ).
• A started service can be created in two ways:
• By extending Service class
• By extending IntentService class
Started Service

7. • If Service class is extended, service runs for
indefinite time. It is destroyed only if activity
destroys it using stopService( ) function.
• If IntentService class is extended, service is
immediately destroyed once its task is
completed.
• Service can destroy itself by calling stopSelf()
method.

8. • Usually, a started service performs a single
operation and does not return a result to the
caller.
• For example, it might download or upload a
file over the network. When the operation is
done, the service should stop itself.

9. Bound Service

10. • A service is "bound" when an application
component binds to it by calling bindService().
• A bound service offers a client-server interface
that allows components to interact with the
service, send requests and get results.
Bound Service

11. • A bound service runs only as long as at least
one application component is bound to it.
• Multiple components can bind to the service
at once, but when all of them unbind, the
service is destroyed.

12. Examples

13. Example 1
[started service by extending Service class]
Display two buttons on Screen : “START
METHOD” and “STOP METHOD”.
When user clicks on “START METHOD”, service
should start. When user clicks on “STOP
METHOD”, service should be stopped.

14. Two .java files should be present in your project:
• Service1Activity.java
• MyService1.java.

15. public class Service1Activity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
public void startMethod(View v)
{
Intent i = new Intent(this,MyService1.class);
i.putExtra("message1","Hello to MyService1");
startService(i);
}
Service1Activity.java

16. public void stopMethod(View v)
{
Intent i = new Intent(this,MyService1.class);
stopService(i);
}
}

17. public class MyService1 extends Service {
@Override
public IBinder onBind(Intent arg0) {
// TODO Auto-generated method stub
return null;
}
@Override
public void onCreate() {
// TODO Auto-generated method stub
Toast.makeText(this, "Service Created",10).show();
super.onCreate();
}
MyService1.java

18. @Override
public int onStartCommand(Intent intent, int flags, int startId) {
// TODO Auto-generated method stub
String msg = intent.getStringExtra("message1");
Toast.makeText(this, "Service Started" + msg,10).show();
return super.onStartCommand(intent, flags, startId);
}
@Override
public void onDestroy() {
// TODO Auto-generated method stub
Toast.makeText(this, "Service Destroyed",10).show();
super.onDestroy(); }
} // end of class MyService1

19. • Service is started using startService(i) call.
Intent i contains name of service class.
• When service is created, onCreate() method is
called by system.
• Then onStartCommand() is called by system.
• Service is not destroyed automatically.
• stopService(i) destroys the service.

20. • When service is destroyed, onDestroy()
method is called by system.
• Thus life cycle of Started service contains
three callback methods: onCreate,
onStartCommand() and onDestroy().

21. Example 2
[started service by extending IntentService
class].
• GUI is same as Example 1.
• Implement service in demoIntentService.java.
• Use same activity file. Make appropriate
changes in Activity file.

22. public class demoIntentService extends IntentService{
public demoIntentService() {
super("Intent Service");
// TODO Auto-generated constructor stub
}
@Override
protected void onHandleIntent(Intent intent) {
// TODO Auto-generated method stub
String msg = intent.getStringExtra("message1");
Toast.makeText(this, "onHandleIntent called" + msg,
Toast.LENGTH_LONG).show();
Log.d("handleIntent","it is called");
}
demoIntentService.java

23. @Override
public void onCreate() {
// TODO Auto-generated method stub
Toast.makeText(this, "onCreate called", Toast.LENGTH_LONG).show();
super.onCreate();
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
// TODO Auto-generated method stub
Toast.makeText(this, "onStartCommand called",
Toast.LENGTH_LONG).show();
onHandleIntent(intent);
super.onStartCommand(intent, flags, startId);

24. return 1;
}
@Override
public void onDestroy() {
// TODO Auto-generated method stub
Toast.makeText(this, "onDestroy called", Toast.LENGTH_LONG).show();
super.onDestroy();
}
}

25. • When service starts, onCreate() is called. Then
onStartCommand().
• From onStartCommand(), onHandleIntent() is
explicitly called.
• Service is destroyed on its own once
onHandleIntent() is completed.

26. Example 3
[Bound service by extending Service class].
GUI has three buttons, “BIND SERVICE”,
“UNBIND SERVICE”, “FIND FACTORIAL”.
One EditText control is present. User enters a
number in it. Then clicks on “FIND
FACTORIAL”. Service finds factorial of given
number.

27. public class Service2Activity extends Activity {
/** Called when the activity is first created. */
MyService mservice;
boolean status;
EditText number;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
number = (EditText)findViewById(R.id.editText1);
}
Service2Activity.java

28. public void bindMethod(View v){
Intent intent = new Intent(this, MyService.class);
bindService(intent, sc, Context.BIND_AUTO_CREATE);
Toast.makeText(Service2Activity.this, "bindMethod called",
Toast.LENGTH_LONG).show();
}
public void unbindMethod(View v){
unbindService(sc);
status = false;
Toast.makeText(Service2Activity.this, "unbindMethod called",
Toast.LENGTH_LONG).show();
}

29. public void factorialMethod(View v)
{
if(status)
{
int num,fact;
num = Integer.parseInt(number.getText().toString());
fact = mservice.findFactorial(num);
Toast.makeText(this,"Factorial is " +
fact,Toast.LENGTH_LONG).show();
}
}

30. private ServiceConnection sc = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName arg0, IBinder arg1) {
// TODO Auto-generated method stub
Toast.makeText(Service2Activity.this, "onServiceConnected started",
Toast.LENGTH_LONG).show();
LocalBinder binder = (LocalBinder)arg1;
mservice = binder.getService();
status = true;
Toast.makeText(Service2Activity.this, "onServiceConnected completed",
Toast.LENGTH_LONG).show();
}

31. @Override
public void onServiceDisconnected(ComponentName arg0) {
// TODO Auto-generated method stub
status = false;
Toast.makeText(Service2Activity.this, "onServiceDisConnected called",
Toast.LENGTH_LONG).show();
}
}; // end of ServiceConnection class
} // end of Activity class

32. public class MyService extends Service {
public final IBinder mbinder = new LocalBinder();
@Override
public IBinder onBind(Intent arg0) {
// TODO Auto-generated method stub
Toast.makeText(this, "IBinder called", Toast.LENGTH_LONG).show();
return mbinder;
}
public class LocalBinder extends Binder{
public MyService getService(){
Toast.makeText(MyService.this, "LocalBinder.getService() called",
Toast.LENGTH_LONG).show();
return MyService.this;}
}
MyService.java

33. public int findFactorial(int x){
int fact = 1;
for(int i=1;i<=x;i++)
{
fact = fact * I;
}
return fact;
}
@Override
public void onCreate() {
// TODO Auto-generated method stub
super.onCreate();
Toast.makeText(this,"Service created", Toast.LENGTH_LONG).show();
}

34. @Override
public void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
Toast.makeText(this,"Service Destroyed", Toast.LENGTH_LONG).show();
}
}

35. • When user clicks on “BIND SERVICE”,
bindMethod() is called.
• In bindMethod(), bindService() is invoked. It is
an in-built method.
• bindServie() contains following arguments:
intent, service connection and flag.

36. • As next step, service is created if it is not
running.
• When service is created, onCreate( ) is called.
Then onBind() is called.
• Object returned by onBind() is stored in ‘arg1’
in onServiceConnected() method of
ServiceConnection class.

37. • ‘arg1’ is assigned to ‘binder’ object in the
same method.
• Then getService() method is called. Its return
value is assigned to mservice object.
• mservice is object of MyService class.
• When user clicks on “FindFactorial”,
findFactorial() method of MyService.java is
called.

38. • Bound service created by above example is
local to application.
• Second way of creating bound service is to use
Messenger class.
• If Messenger class is used, service can be used
by a component outside the application
hosting the service.

39. • Find answer of following question yourself :
When onServiceDisconnected() is called ?

40. Example 4
[bound service by using Messenger class].
Activity sends a message to service. Service
receives the message and displays it.
Refer to service3.tar uploaded in edmodo for
detailed code.

41. • Following files are uploaded in edmodo:
• Service1.tar – for started service
• Service2.tar – for bound service (example 3)
• Service3.tar – for example 4

42. • We have discussed about started and bound
services.
• Each of them can be created in two different
ways.
• Services are different than Activities. They
don’t have GUI.
Summary

43. • Website: developer.android.com
• Chapter 21, Working with Services from
Android Wireless Application Development
by Darcy and Conder
• Videos shared on FTP
Readings