Develop Reference

What does the Binder class do? What is the meaning of binding in Android bound services?

I am totally confused with bound services. My questions are:
What is the meaning of binding?
What does the Binder class do?
What is meant by "returns an IBinder for interacting with the service"?
What is the IBinder object?
How does the onBind() method work?
These are the a questions on bound services. Please explain in detail. I have already read the documentation, but it is still unclear to me.

Bound service:
A bound service is one that allows application components to bind to it by calling bindService() to create a long-standing connection.
Create a bound service when you want to interact with the service from activities and other components in your application or to expose some of your application's functionality to other applications through interprocess communication (IPC).
To create a bound service, implement the onBind() callback method to return an IBinder that defines the interface for communication with the service. Other application components can then call bindService() to retrieve the interface and begin calling methods on the service. The service lives only to serve the application component that is bound to it, so when there are no components bound to the service, the system destroys it. You do not need to stop a bound service in the same way that you must when the service is started through onStartCommand().
IBinder:
To create a bound service, you must define the interface that specifies how a client can communicate with the service. This interface between the service and a client must be an implementation of IBinder and is what your service must return from the onBind() callback method. After the client receives the IBinder, it can begin interacting with the service through that interface.
onBind():
The system invokes this method by calling bindService() when another component wants to bind with the service (such as to perform RPC). In your implementation of this method, you must provide an interface that clients use to communicate with the service by returning an IBinder. You must always implement this method; however, if you don't want to allow binding, you should return null.

this is an example works as completion to the answer above
inside your service class, initialize the IBinder interface with the object created by our inner class (check step 2)
create an inner class extends Binder that has a getter function, to gain access to the service class
in your service class ovveride onBind function, and use it to return the instance we created in step 1
**The code will clear it for you **
public class MyServiceClass extends Service {
//binder given to client
private final IBinder mBinder = new LocalBinder();
//our inner class
public LocalBinder extends Binder {
public MyServiceClass getService() {
return MyServiceClass.this;
}
}
#Override
public IBinder onBind(Intent intent) {
return mBinder;
}
public void doSomeWork(int time){ //we will call this function from outside, which is the whole idea of this **Binding**}
}
Next step is binding itself
in your MainClass or whatever where you want to bind your service,
Defines callbacks for service binding, passed to bindService()
private ServiceConnection serviceConnection = new ServiceConnection(){
#Override
public void onServiceConnected(ComponentName className, IBinder service) {
MyServiceClass.LocalBinder binder =(MyServiceClass.LocalBinder)service;
timerService = binder.getService();
}
#Override
public void onServiceDisconnected(ComponentName arg0) {
//what to do if service diconnect
}
};
the moment of binding
Intent intent = new Intent(this, MyServiceClass.class);
bindService(intent, serviceConnection, Context.BIND_AUTO_CREATE);
to unbind the service
unbindService(serviceConnection);
then you call the public function we created before in the Service class using the help of [timerService = binder.getService();]
timerService.doSomeWork(50);

Why a Null Pointer when trying to use Android Local Bound Service?

In the Service class:
class AeroBluetoothService extends Service { ...
private final IBinder asBleBinder = new LocalBinder();
public class LocalBinder extends Binder {
AeroBluetoothService getService() {
return AeroBluetoothService.this;
}
}
#Override
public IBinder onBind(Intent intent) {
return asBleBinder;
}
In the client Activity:
Intent bindAsBleIntent;
#Override
public void onServiceConnected( ComponentName className, IBinder service ) {
AeroBluetoothService.LocalBinder asBleBinder = (AeroBluetoothService.LocalBinder) service;
asBleServiceRef = asBleBinder.getService();
}
In Client's onCreate():
bindAsBleIntent = new Intent( getApplicationContext(), AeroBluetoothService.class );
bindService( bindAsBleIntent, /*ServiceConnection*/ this, Context.BIND_AUTO_CREATE );
The problem is that when I try to call a Service method from the Client:
asBleServiceRef.scanForAero();
the reference to the Service instance, asBleServiceRef, is null. It is as though the onServiceConnected() callback is not being called (or is passing a null argument).
I copied this code quite carefully from an Android example. I just noticed that the example calls bindService() from its onStart() method, whereas I'm calling from onCreate(). Could that make any difference? What's the problem?

As #avinash correctly saw, the problem was simply neglecting to declare the Service in the Manifest.

Passing data from Activity to IntentService (Android SDK)

I create a service that is running in the background for the entire duration of application.
I chose an IntentService for this.
For me intent.putExtra(....) work only on start the service.
My problem is that sometimes I want to passing data from Activity to IntentService not only at start.
Thank You

Just transfer data to IntentService by start, because the IntentService will always has the only one instance in the whole application life cycle.

You can use bind interface to interact with service public methods.
From documentation:
public class LocalService extends Service {
// Binder given to clients
private final IBinder mBinder = new LocalBinder();
// Random number generator
private final Random mGenerator = new Random();
/**
* Class used for the client Binder. Because we know this service always
* runs in the same process as its clients, we don't need to deal with IPC.
*/
public class LocalBinder extends Binder {
LocalService getService() {
// Return this instance of LocalService so clients can call public methods
return LocalService.this;
}
}
#Override
public IBinder onBind(Intent intent) {
return mBinder;
}
/** method for clients */
public int getRandomNumber() {
return mGenerator.nextInt(100);
}
}

Accessing a method of a bound service from an IntentReceiver on Android

I'm having a service class that I bind from my main activity with a ServiceConnection to call a method within the service as soon as it is bound. I need to explicitly call the method to pass over the context of my main activity.
If I call this service class from within an IntentReceiver, I need to use peekService to bind to the service. But how can I spawn it's method then? :-s
Best regards / Thanks alot!
S.

peekService returns you IBinder implementation. you need only to call getService() from it and you will get your service object.
Put your code inside your service:
public class LocalBinder extends Binder {
public NotificationService getService() {
return NotificationService.this;
}
}
#Override
public IBinder onBind(Intent intent) {
return new LocalBinder();
}

Android service running after pressing Home key

I have an Android service, created in OnCreate of first Activity of the application using StartService(). I need this service to be running throughout the life span of the application ie, all the activities in the application. But the service should not consume the resources after user pressed Home key or Back button. Is there any elegant way to do that other than stopping the service in onPause() method of all the activities?

Instead of using StartService, you can call bindService in onResume and unbindService in onPause. Your service will stop when there are no open bindings.
You'll need to create a ServiceConnection to get access to the service. For instance, here's a class nested inside MyService:
class MyService {
public static class MyServiceConnection implements ServiceConnection {
private MyService mMyService = null;
public MyService getMyService() {
return mMyService;
}
public void onServiceConnected(ComponentName className, IBinder binder) {
mMyService = ((MyServiceBinder)binder).getMyService();
}
public void onServiceDisconnected(ComponentName className) {
mMyService = null;
}
}
// Helper class to bridge the Service and the ServiceConnection.
private class MyServiceBinder extends Binder {
MyService getMyService() {
return MyService.this;
}
}
#Override
public IBinder onBind(Intent intent) {
return new MyServiceBinder();
}
#Override
public boolean onUnbind(Intent intent) {
return false; // do full binding to reconnect, not Rebind
}
// Normal MyService code goes here.
}
One can use this helper class to get access to the service via:
MyServiceConnection mMSC = new MyService.MyServiceConnection();
// Inside onResume:
bindService(new Intent(this, MyService.class), mMSC, Context.BIND_AUTO_CREATE);
// Inside onPause:
unbindService(mMSC);
// To get access to the service:
MyService myService = mMSC.getMyService();

You could do what Darrell suggests but put that code in a new class that extends Activity and then extend that on all your normal Activities.
I don't know any other more elegant way of achieving your goals.