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);

Interaction between IntentService and Activity - Android

In my application I am using an IntentService to download a file from a cloud. And showing the progress in NotificationManager. I need to show the status (Downloading/Completed or Failed) in the Activity which stared the IntentService too.
My problem is once I closed the app and open it back, I want to get the status of downloading from IntentService.
Which is the best way to do this?

You can let your Activity bind to your Service, by calling bindService() in your Activity. As per the documentation:
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, get results, and even do so across processes with
interprocess communication (IPC). A bound service runs only as long as
another 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.
Also:
You should 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).
The documentation provides a fully functional example of this. Below is taken from the provided link.
Service class:
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);
}
}
Activity class:
public class BindingActivity extends Activity {
LocalService mService;
boolean mBound = false;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
#Override
protected void onStart() {
super.onStart();
// Bind to LocalService
Intent intent = new Intent(this, LocalService.class);
bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
}
#Override
protected void onStop() {
super.onStop();
// Unbind from the service
if (mBound) {
unbindService(mConnection);
mBound = false;
}
}
/** Called when a button is clicked (the button in the layout file attaches to
* this method with the android:onClick attribute) */
public void onButtonClick(View v) {
if (mBound) {
// Call a method from the LocalService.
// However, if this call were something that might hang, then this request should
// occur in a separate thread to avoid slowing down the activity performance.
int num = mService.getRandomNumber();
Toast.makeText(this, "number: " + num, Toast.LENGTH_SHORT).show();
}
}
/** Defines callbacks for service binding, passed to bindService() */
private ServiceConnection mConnection = new ServiceConnection() {
#Override
public void onServiceConnected(ComponentName className,
IBinder service) {
// We've bound to LocalService, cast the IBinder and get LocalService instance
LocalBinder binder = (LocalBinder) service;
mService = binder.getService();
mBound = true;
}
#Override
public void onServiceDisconnected(ComponentName arg0) {
mBound = false;
}
};
}
In your Service, you can define public methods that your Activity can call, such as polling for your download progress. Please refer to the documentation for explanation in detail.

There are couple of ways to have communication connection between Service and Activity. I would suggest these 2
First, you can use the great library Otto. With Otto, you can also have #Produce annotated method. With this method you will return the latest information about the download. When you #Subscribe in your Activity you will get the latest info immediately. https://github.com/square/otto
If you are using Android built-in DownloadManager it returns the updates and results with a Broadcast, you can register to that Broadcast both in your Service and Activity. This way you will be able to update both of them. I suggest you to use DownloadManager, it is awesome.
http://developer.android.com/reference/android/app/DownloadManager.html

How to bind to a Service that was started by another instance of the application

I have a background Service that need to be running even if the application gets killed by Android. This is currently working perfectly.
My problem is that when I restart the application (with the background service still running), I want my Activity to bind to the service to have access to some of its methods. When I try to bind with a ServiceConnection, the onServiceConnected is never called.
final private ServiceConnection serviceConnection = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder service) {
Log.d(TAG, "onServiceConnected"); //this is never called
MyBackgroundService.ServiceBinder binder = (MyBackgroundService.ServiceBinder) service;
backgroundService = binder.getService();
}
public void onServiceDisconnected(ComponentName className) {
Log.d(TAG, "onServiceDisconnected");
backgroundService = null;
}
};
private void bindBackgroundService(){
this.bindService(new Intent(this, MyBackgroundService.class), serviceConnection, Context.BIND_AUTO_CREATE);
}
Am I doing this the wrong way? Is it better to stop the Service and restart it?

Since the class that binded the background service is a singleton and my alarm broadcast receiver that is making sure the background service is always running instantiates this singleton, I had access to this singleton and I was trying to bind to the service that was already binded.

Android: Getting a variable from my running service

My activity starts a Service, and when I close my app, the service continues to run.
OK, that's right. But when I open my application again, in the activity, I need to know the value of a public variable defined on the running Service(class) that I've started previously.
How can I do that?
Thanks

If you are binding your Activity to the Service, you should have an implementation of the Binder interface in your Service, e.g.
public class ServiceBinder extends Binder {
public MyService getService() {
return MyService.this;
}
}
In your Activity, create a new ServiceConnection class which will be used to give you access to your Service:
private ServiceConnection mConnection = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder service) {
mMyService = ((MyService.ServiceBinder)service).getService();
}
public void onServiceDisconnected(ComponentName className) {
mMyService = null;
}
};
Here the member variable mMyService will give you access to all public members of your Service class.
To create the connection, implement doBindService and doUnbindService in your Activity:
void doBindService() {
bindService(new Intent(this, MyService.class), mConnection, Context.BIND_AUTO_CREATE);
}
void doUnbindService() {
// Detach our existing connection.
unbindService(mConnection);
}
Hope this helps!

If you don't call unbindService, your activity still have connection to service and you can simply check the variable through the service's method.

You could use messenger.
As per android website
A messenger is reference to a Handler, which others can use to send messages to it. This allows for the implementation of message-based communication across processes, by creating a Messenger pointing to a Handler in one process, and handing that Messenger to another process.

How to call an Android remote service (IPC) from a Widget / local service?

I'm trying to remote control a live wallpaper from a widget. They're in the same APK, but obviously different processes. Calling an "activity" of the live wallpaper is of little use to me since it is a different process. The widget has simple buttons that, when pressed,
So what (I think) I need is IPC and AIDL.
First I created the AIDL on the wallpaper side, which worked fine. It has three methods with no extra parameters. But when I added the clientside to the widget, I got an error telling me that I cannot bind to that remote interface because the widget is already a BroadcastListener. I tried getting button handling in without needing the Widget to be a BroadcastListener, but that seems to be impossible.
Well no problem, right? I just created a service within the widget that binds to the remote interface, because while the widget is a BroadcastListener, the service is not, and everything should be fine.
Or so I thought.
Well, I'm getting the widget's buttons to trigger the widget service. Binding to the remote service yields me the following warning:
Unable to start service Intent (act=com.blabla.IRemoteService): not found.
I am using getApplicationContext() within the service of the widget to bind to the remote stuff. I do have the widget service in the manifest, but I don't have the remote service in there. When I do put it in there, I get a nonspecific InstantiationException.
In the Widget's Service onStart() I am doing this:
getApplicationContext().bindService(new Intent(IWallpaperRemote.class.getName()),
mConnection, Context.BIND_AUTO_CREATE);
I also have...
private ServiceConnection mConnection = new ServiceConnection() {
public void onServiceConnected(ComponentName className,
IBinder service) {
mService = IWallpaperRemote.Stub.asInterface(service);
isBound = true;
Log.i("WidgetServiceConnection", "binding to service succeeded");
}
public void onServiceDisconnected(ComponentName className) {
mService = null;
isBound = false;
Log.i("WidgetServiceConnection", "binding to service lost!");
}
};
My question is this: Has anyone ever successfully done a remote call from a widget into another application? Considering I am talking about a live wallpaper here, and the fact that I'm not interested in calling an activity within the widget process but cause function calls within the live wallpaper, what options do I have other than IPC, if any?
And if IPC is the way to go here, what am I doing wrong?

I found the answer to my own question. To make things easier for others, here's the solution:
When doing a remote service, one has to write the AIDL which will be compiled into a sort of stub interface, the implementation of that interface (i.e. the code that is executed when someone calls the remote methods), and a class that extends "Service" which returns the implementation class in the onBind() method. (A normal local service would return null in that method)
Now what I had not understood is that you MUST have a service definition in the manifest - WITH INTENT FILTER!
Let's say your AIDL is called IRemoteService.aidl, then you have a class called RemoteService which looks like this:
public class RemoteService extends Service {
public IBinder onBind(Intent intent) {
Log.i("RemoteService", "onBind() called");
return new RemoteServiceImpl();
}
/**
* The IRemoteInterface is defined through IDL
*/
public class RemoteServiceImpl extends IRemoteService.Stub {
public void remoteDetonateBirthdayCake() throws RemoteException {
//your code here
}
};
}
In your android manifest, you want this:
<service android:name="RemoteService">
<intent-filter>
<action android:name="com.sofurry.favorites.IRemoteService"></action>
</intent-filter>
</service>
Note the service name: It's "RemoteService", not "IRemoteService" or even "RemoteServiceImpl". You need the name of the class that extends "Service", whose onBind method we overrode.
To complete the thing, here's the code on the client side -and yes this code also works from within another service, for example one you started from your widget ;)
IRemoteService mService;
RemoteServiceConnection mConnection = new RemoteServiceConnection();
getApplicationContext().bindService(new Intent(IRemoteService.class.getName()), mConnection, Context.BIND_AUTO_CREATE);
...where RemoteServiceConnection can be an inner class like so:
class RemoteServiceConnection implements ServiceConnection {
public void onServiceConnected(ComponentName className,
IBinder service ) {
mService = IRemoteService.Stub.asInterface(service);
isBound = true;
}
public void onServiceDisconnected(ComponentName className) {
mService = null;
isBound = false;
}
};
And now, you're free to call..
mService.remoteDetonateBirthdayCake();
In summary: Be sure to have a service stanza in the android manifest, set "name" to the class that returns the actual implementation in its onBind() method, and you must also have an intent filter with an action definiton that points to the AIDL interface.
Hint: If you are calling remote services from an app inside a different APK, add a "category" element to the intent filter too, and set it to DEFAULT.