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I have an App (Client) that performs remote calls using AIDL to a second App (Server). Each call to through the Binder is executed in the Server app in a different thread (TID) as designed by AIDL solution.
Is it possible to make all calls executed in the Server app be executed in just one thread? We have control over all callers (Client apps) and they will perform call in a serial mode and we don't need Server app perform the calls in a multithread way.
So, if the Client App 1 performs a remote call to a method that takes 30 seconds and before it, a second Client App 2 performs a call to the same method (or even other method) we want this second call be executed in the same Thread of the first call.
Messenger is not an option for now.
=== Updated ====
Message is not an option (for now). Here more details: We have a service with 2 type of binders: a) TransacionManager (tm) and DAOImpl (dao).
We first do a call to tm.begin() in the client and even its processed synchronously, on the Service side its is executed in a thread from Thread Pool (android aidl code). This thread TID #1 performs the begin transaction command in SQLite database.
Then we do a call to dao.selectNextId() - synchronously - and in the Service it is executed in the TID #2. In the selectNextId() method we check if the database is inTransaction and it returns false.
To confirm that the threads was the problem, we put everything in a single call to another binder (allDAO). So when we call allDAO.do() it runs on the Service side in another thread TID #3 and performs begin transc and insert very well.
Not sure if the problem is SQLite that manage different threads as separated requests (how to deal with)... We just want the Service (using aidl) perform every call from any clients in a same single thread everytime.
I was working with Mario on this issue and using the #pskink's code snippet we solved the multithreading issue.
The issue was solved redirecting all aidl calls to the main thread. To do this, we used a Handler thats receives the MainLooper and a Runnable that extends CountDownLatch.
The code of our solution bellow:
// SyncHandler.class
public class SyncHandler {
private SyncRunnable mRunnable;
public SyncHandler() {
super();
}
public SyncHandler start(#NonNull SyncRunnable runnable) {
mRunnable = runnable;
final Looper looper = Looper.getMainLooper();
Handler handler = new Handler(looper);
handler.post(mRunnable);
try {
mRunnable.await();
} catch (InterruptedException e) {
Log.e(this, "Error when SyncHandler was awaiting.", e);
}
return this;
}
public static class ReturnValue<T> {
public T value;
}
}
// SyncRunnable.class
public final class SyncRunnable extends CountDownLatch implements Runnable {
private Runnable mRunnable;
public static SyncRunnable create(Runnable runnable) {
return new SyncRunnable(runnable);
}
private SyncRunnable(Runnable runnable) {
super(1);
mRunnable = runnable;
}
#Override
public void run() {
Log.d(this, "SyncRunnable.run() executed on thread: " + Thread.currentThread());
mRunnable.run();
countDown();
}
}
//And the database call:
// TransactionManager.class
public synchronized void begin(final int ownerHashCode, String ownerName) throws RemoteException {
SyncHandler handler = new SyncHandler().start(SyncRunnable.create(new Runnable() {
#Override
public void run() {
if (mOwner == null) {
mOwner = ownerHashCode;
for (Database database : mDatabases) {
database.beginTransaction();
}
} else if (mOwner == ownerHashCode) {
throw new DbTransactionException("Error: TransactionOwner == owner");
}
}
}));
}
// DaoHelper.class
public synchronized long insert(Dao dao) {
final SyncHandler.ReturnValue<Long> value = new SyncHandler.ReturnValue<>();
SyncHandler handler = new SyncHandler().start(SyncRunnable.create(new Runnable() {
#Override
public void run() {
Log.d(DaoHelper.this, "db.inTransaction: " + mManagerDb.getDatabase().inTransaction());
value.value = mManagerDb.getDatabase().insert(mTable, null, mContentValues);
}
}));
return value.value;
}
I have a handler object as below, just an example
My question is: if someone calls dataSync.setDataEnabled(true) then call dataSync.getDateEnabled() immediately. Can we make sure set/get still execute in order in dataSync class? Because we use message to write data but read data directly.
Thanks
class dataSync extends Handler {
...
#Override
public void handleMessage(Message msg) {
case CMD_SET_DATA_ENABLE_SYN:
final boolean enabled = ((boolean)msg.arg1) ? true : false;
setDataEnabledSync(enabled);
break;
}
public boolean getDateEnabled() {
sync (mLock) {
return mDataEnabled;
}
}
void setDataEnabled(boolean enable) {
Message msg = obtainMessage(CMD_SET_DATA_ENABLE_SYNC);
msg.arg1 = enable ? 1 : 0;
sendMessage(msg);
}
void setDataEnabledSync(enabled); {
sync (mLock) {
mDataEnabled = enabled;
}
}
}
The answer to the question is YES! It could be happen in this scenario.
"dataSync" this handler will queue the message and execute "in order call", BUT another thread will call "getDateEnabled()" immediately.
So when "dataSync" handler queue a lot messages it will go wrong.
I have created IntentService with infinite loop inside the onHandleIntent then add static methods start,resume,pause,stop to directly call it within my Activities.
The scenario is, inside the infinite loop, I am calling callback methods which is creating a new thread to execute long process.
The problem is, I am worrying about continuously creating Threads due to infinite loop. I am pretty sure that there is better way to manage it. I am thinking of ThreadPool or something enable to use only one thread in a sequential manner. So that, I am saving time,memory,overheads etc..
OTHER APPROACH ARE VERY WELCOME. Ask me other information as needed. Then, I will update here.
Here are my codes(take a look at SampleCallback):
IntentService
import android.app.IntentService;
import android.content.Intent;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
public class SampleCallbackIntentService extends IntentService {
private final String LOG_LOGCAT_TAG = "SampleCallbackIntentService";
private Handler _handler;
public SampleCallbackIntentService(String name) {
super(name);
}
#Override
public void onCreate() {
super.onCreate();
// initialize variables for pause & resume thread
_mPauseLock = new Object();
_mPaused = false;
_mFinished = false;
// initialize handler to switch to UI/Main thread
_handler = new Handler()
{
#Override
public void handleMessage(final Message msg)
{
_callback.doSomethingFromUIThread(msg);
}
};
}
private final SampleCallback _callback = new SampleCallback() {
#Override
public void doSomethingFromCurrentThread(final Object object) {
new Thread(new Runnable() {
#Override
public void run() {
//do long running process.
// I will access object here.
}
}).start();
}
#Override
public void doSomethingFromUIThread(final Message msg) {
//may update UI here.
}
};
private final int CALLBACK_MESSAGE = 1;
#Override
protected void onHandleIntent(Intent arg0) {
Log.i(LOG_LOGCAT_TAG, "loop started");
while (!_mFinished) {
// do stuff here
// create the object variable. Then pass to callback method
_callback.doSomethingFromCurrentThread(object);
// process and create the result to pass
String someResult = "some result here";
_handler.sendMessage(_handler.obtainMessage(CALLBACK_MESSAGE, someResult));
synchronized (_mPauseLock) {
while (_mPaused) {
try {
Log.i(LOG_LOGCAT_TAG, "loop paused");
_mPauseLock.wait();
Log.i(LOG_LOGCAT_TAG, "loop resumed");
} catch (InterruptedException e) {
Log.e(LOG_LOGCAT_TAG, "error occured on pause", e);
}
}
}
try {
//using sleep here might be not good design.
Thread.sleep(1000);
} catch (InterruptedException e) {
Log.e(LOG_LOGCAT_TAG, "error occured on sleep", e);
}
}
Log.i(LOG_LOGCAT_TAG, "loop ended");
}
private static Object _mPauseLock;
private static boolean _mPaused;
private static boolean _mFinished;
public static void start(Context context) {
Intent service = new Intent(context, SampleCallbackIntentService .class);
if(context.startService(service)==null) {
Log.e(LOG_LOGCAT_TAG, "Service cannot be started");
} else {
Log.i(LOG_LOGCAT_TAG, "start() called");
}
}
/**
* Call this on pause.
*/
public static void pause() {
Log.i(LOG_LOGCAT_TAG, "pause() called");
synchronized (_mPauseLock) {
_mPaused = true;
}
}
/**
* Call this on resume.
*/
public static void resume() {
Log.i(LOG_LOGCAT_TAG, "resume() called");
synchronized (_mPauseLock) {
_mPaused = false;
_mPauseLock.notifyAll();
}
}
public static void stop() {
if(_mPauseLock == null) return;
synchronized (_mPauseLock) {
Log.i(LOG_LOGCAT_TAG, "stop() called");
_mFinished = true;
}
}
}
SampleCallback
import android.os.Message;
public interface SampleCallback {
public void doSomethingFromCurrentThread(final Object object);
public void doSomethingFromUIThread(final Message msg);
}
UPDATES1
I am using location api aside from google api. I will create a android library project and use that api to get the latest location (e.g. every 2secs) in the background.
On the application side, just need to call static methods to use it (e.g. start(context, callback), pause(), resume(), stop()). It has callbacks to obtain the location. After obtaining the needed information from the location object, I will create a new thread to call my own created callbacks (which implemented by the application side).
You can use AsyncTask instead of creating a new thread every time? AsyncTask manages a fixed pool of threads (or one background thread - depending on Android version) and allows to perform background operations and publish results on the UI thread without having to manipulate threads and/or handlers.
However I wonder why do you need to create an infinite loop inside the onHandleIntent method? By doing that you prevent your IntentService from receiving further Intents. Since in IntentService:
All requests are handled on a single worker thread -- they may take as
long as necessary (and will not block the application's main loop),
but only one request will be processed at a time.
I think you want to execute some long-running code out of the UI thread in the IntentService. But that doesn't require the creation of an infinite loop in the IntentService worker thread. Just send the requests as needed to the IntentService using Context.startService(Intent) call. If you want IntentService to send back some result or just call a callback in the UI thread you can pass a Messenger (or a ResultReceiver) object with the Intent.
Activity:
final Handler uiHandler = new Handler(Looper.getMainLooper());
private void postTask() {
Intent intent = new Intent("com.yourservice.DOACTION");
intent.putExtra("messenger", new Messenger(handler));
intent.putExtra("object", YourObject()); // pass other Parcelable objects
startService(intent);
}
IntentService:
protected void onHandleIntent(Intent intent) {
Messenger messenger = intent.getParcelableExtra("messenger");
YourObject object = intent.getParcelableExtra("object");
//... do work here ...
Message msg = Message.obtain();
msg.what = CALLBACK_MESSAGE;
msg.setData(someResult);
messenger.send(Message.obtain());
}
Look into the docs for ExecutorService (not to be confused with Android Services) and the Executors package. There are a few examples there on how to use thread pools.
So wait, why do you need to use all these callbacks? Can't you just have each intent encode what needs to be done and then have your onHandleIntent execute different code based on the information of the intent. This is the way IntentService is intended to be used.
You shouldn't be doing any of the thread handling in the IntentSerivce. The IntentService is supposed to be handling all the threading code (and you should let it because it's probably highly optimized).
I'm looking to make a service which I can use to make calls to a web-based REST API.
Basically I want to start a service on app init then I want to be able to ask that service to request a url and return the results. In the meantime I want to be able to display a progress window or something similar.
I've created a service currently which uses IDL, I've read somewhere that you only really need this for cross app communication, so think these needs stripping out but unsure how to do callbacks without it. Also when I hit the post(Config.getURL("login"), values) the app seems to pause for a while (seems weird - thought the idea behind a service was that it runs on a different thread!)
Currently I have a service with post and get http methods inside, a couple of AIDL files (for two way communication), a ServiceManager which deals with starting, stopping, binding etc to the service and I'm dynamically creating a Handler with specific code for the callbacks as needed.
I don't want anyone to give me a complete code base to work on, but some pointers would be greatly appreciated.
Code in (mostly) full:
public class RestfulAPIService extends Service {
final RemoteCallbackList<IRemoteServiceCallback> mCallbacks = new RemoteCallbackList<IRemoteServiceCallback>();
public void onStart(Intent intent, int startId) {
super.onStart(intent, startId);
}
public IBinder onBind(Intent intent) {
return binder;
}
public void onCreate() {
super.onCreate();
}
public void onDestroy() {
super.onDestroy();
mCallbacks.kill();
}
private final IRestfulService.Stub binder = new IRestfulService.Stub() {
public void doLogin(String username, String password) {
Message msg = new Message();
Bundle data = new Bundle();
HashMap<String, String> values = new HashMap<String, String>();
values.put("username", username);
values.put("password", password);
String result = post(Config.getURL("login"), values);
data.putString("response", result);
msg.setData(data);
msg.what = Config.ACTION_LOGIN;
mHandler.sendMessage(msg);
}
public void registerCallback(IRemoteServiceCallback cb) {
if (cb != null)
mCallbacks.register(cb);
}
};
private final Handler mHandler = new Handler() {
public void handleMessage(Message msg) {
// Broadcast to all clients the new value.
final int N = mCallbacks.beginBroadcast();
for (int i = 0; i < N; i++) {
try {
switch (msg.what) {
case Config.ACTION_LOGIN:
mCallbacks.getBroadcastItem(i).userLogIn( msg.getData().getString("response"));
break;
default:
super.handleMessage(msg);
return;
}
} catch (RemoteException e) {
}
}
mCallbacks.finishBroadcast();
}
public String post(String url, HashMap<String, String> namePairs) {...}
public String get(String url) {...}
};
A couple of AIDL files:
package com.something.android
oneway interface IRemoteServiceCallback {
void userLogIn(String result);
}
and
package com.something.android
import com.something.android.IRemoteServiceCallback;
interface IRestfulService {
void doLogin(in String username, in String password);
void registerCallback(IRemoteServiceCallback cb);
}
and the service manager:
public class ServiceManager {
final RemoteCallbackList<IRemoteServiceCallback> mCallbacks = new RemoteCallbackList<IRemoteServiceCallback>();
public IRestfulService restfulService;
private RestfulServiceConnection conn;
private boolean started = false;
private Context context;
public ServiceManager(Context context) {
this.context = context;
}
public void startService() {
if (started) {
Toast.makeText(context, "Service already started", Toast.LENGTH_SHORT).show();
} else {
Intent i = new Intent();
i.setClassName("com.something.android", "com.something.android.RestfulAPIService");
context.startService(i);
started = true;
}
}
public void stopService() {
if (!started) {
Toast.makeText(context, "Service not yet started", Toast.LENGTH_SHORT).show();
} else {
Intent i = new Intent();
i.setClassName("com.something.android", "com.something.android.RestfulAPIService");
context.stopService(i);
started = false;
}
}
public void bindService() {
if (conn == null) {
conn = new RestfulServiceConnection();
Intent i = new Intent();
i.setClassName("com.something.android", "com.something.android.RestfulAPIService");
context.bindService(i, conn, Context.BIND_AUTO_CREATE);
} else {
Toast.makeText(context, "Cannot bind - service already bound", Toast.LENGTH_SHORT).show();
}
}
protected void destroy() {
releaseService();
}
private void releaseService() {
if (conn != null) {
context.unbindService(conn);
conn = null;
Log.d(LOG_TAG, "unbindService()");
} else {
Toast.makeText(context, "Cannot unbind - service not bound", Toast.LENGTH_SHORT).show();
}
}
class RestfulServiceConnection implements ServiceConnection {
public void onServiceConnected(ComponentName className, IBinder boundService) {
restfulService = IRestfulService.Stub.asInterface((IBinder) boundService);
try {
restfulService.registerCallback(mCallback);
} catch (RemoteException e) {}
}
public void onServiceDisconnected(ComponentName className) {
restfulService = null;
}
};
private IRemoteServiceCallback mCallback = new IRemoteServiceCallback.Stub() {
public void userLogIn(String result) throws RemoteException {
mHandler.sendMessage(mHandler.obtainMessage(Config.ACTION_LOGIN, result));
}
};
private Handler mHandler;
public void setHandler(Handler handler) {
mHandler = handler;
}
}
Service init and bind:
// this I'm calling on app onCreate
servicemanager = new ServiceManager(this);
servicemanager.startService();
servicemanager.bindService();
application = (ApplicationState)this.getApplication();
application.setServiceManager(servicemanager);
service function call:
// this lot i'm calling as required - in this example for login
progressDialog = new ProgressDialog(Login.this);
progressDialog.setMessage("Logging you in...");
progressDialog.show();
application = (ApplicationState) getApplication();
servicemanager = application.getServiceManager();
servicemanager.setHandler(mHandler);
try {
servicemanager.restfulService.doLogin(args[0], args[1]);
} catch (RemoteException e) {
e.printStackTrace();
}
...later in the same file...
Handler mHandler = new Handler() {
public void handleMessage(Message msg) {
switch (msg.what) {
case Config.ACTION_LOGIN:
if (progressDialog.isShowing()) {
progressDialog.dismiss();
}
try {
...process login results...
}
} catch (JSONException e) {
Log.e("JSON", "There was an error parsing the JSON", e);
}
break;
default:
super.handleMessage(msg);
}
}
};
If your service is going to be part of you application then you are making it way more complex than it needs to be. Since you have a simple use case of getting some data from a RESTful Web Service, you should look into ResultReceiver and IntentService.
This Service + ResultReceiver pattern works by starting or binding to the service with startService() when you want to do some action. You can specify the operation to perform and pass in your ResultReceiver (the activity) through the extras in the Intent.
In the service you implement onHandleIntent to do the operation that is specified in the Intent. When the operation is completed you use the passed in ResultReceiver to send a message back to the Activity at which point onReceiveResult will be called.
So for example, you want to pull some data from your Web Service.
You create the intent and call startService.
The operation in the service starts and it sends the activity a message saying it started
The activity processes the message and shows a progress.
The service finishes the operation and sends some data back to your activity.
Your activity processes the data and puts in in a list view
The service sends you a message saying that it is done, and it kills itself.
The activity gets the finish message and hides the progress dialog.
I know you mentioned you didn't want a code base but the open source Google I/O 2010 app uses a service in this way I am describing.
Updated to add sample code:
The activity.
public class HomeActivity extends Activity implements MyResultReceiver.Receiver {
public MyResultReceiver mReceiver;
public void onCreate(Bundle savedInstanceState) {
mReceiver = new MyResultReceiver(new Handler());
mReceiver.setReceiver(this);
...
final Intent intent = new Intent(Intent.ACTION_SYNC, null, this, QueryService.class);
intent.putExtra("receiver", mReceiver);
intent.putExtra("command", "query");
startService(intent);
}
public void onPause() {
mReceiver.setReceiver(null); // clear receiver so no leaks.
}
public void onReceiveResult(int resultCode, Bundle resultData) {
switch (resultCode) {
case RUNNING:
//show progress
break;
case FINISHED:
List results = resultData.getParcelableList("results");
// do something interesting
// hide progress
break;
case ERROR:
// handle the error;
break;
}
}
The Service:
public class QueryService extends IntentService {
protected void onHandleIntent(Intent intent) {
final ResultReceiver receiver = intent.getParcelableExtra("receiver");
String command = intent.getStringExtra("command");
Bundle b = new Bundle();
if(command.equals("query") {
receiver.send(STATUS_RUNNING, Bundle.EMPTY);
try {
// get some data or something
b.putParcelableArrayList("results", results);
receiver.send(STATUS_FINISHED, b)
} catch(Exception e) {
b.putString(Intent.EXTRA_TEXT, e.toString());
receiver.send(STATUS_ERROR, b);
}
}
}
}
ResultReceiver extension - edited about to implement MyResultReceiver.Receiver
public class MyResultReceiver implements ResultReceiver {
private Receiver mReceiver;
public MyResultReceiver(Handler handler) {
super(handler);
}
public void setReceiver(Receiver receiver) {
mReceiver = receiver;
}
public interface Receiver {
public void onReceiveResult(int resultCode, Bundle resultData);
}
#Override
protected void onReceiveResult(int resultCode, Bundle resultData) {
if (mReceiver != null) {
mReceiver.onReceiveResult(resultCode, resultData);
}
}
}
Developing Android REST client applications has been an awesome resource for me. The speaker does not show any code, he just goes over design considerations and techniques in putting together a rock solid Rest Api in android. If your a podcast kinda person or not, I'd recommend giving this one at least one listen but, personally I've listened to it like 4 or five times thus far and I'm probably going to listen to it again.
Developing Android REST client applications
Author: Virgil Dobjanschi
Description:
This session will present architectural considerations for developing RESTful applications on the Android platform. It focuses on design patterns, platform integration and performance issues specific to the Android platform.
And there are so many considerations I really hadn't made in the first version of my api that I've had to refactor
Also when I hit
the post(Config.getURL("login"),
values) the app seems to pause for a
while (seems weird - thought the idea
behind a service was that it runs on a
different thread!)
No you have to create a thread yourself, a Local service runs in the UI thread by default.
I know #Martyn does not want full code, but I think this annotation its good for this question:
10 Open Source Android Apps which every Android developer must look into
Foursquared for Android is open-source, and have an interesting code pattern interacting with the foursquare REST API.
I would highly recommend the REST client Retrofit.
I have found this well written blog post extremely helpful, it also contains simple example code.
The author uses Retrofit to make the network calls and Otto to implement a data bus pattern:
http://www.mdswanson.com/blog/2014/04/07/durable-android-rest-clients.html
Just wanted to point you all in the direction of an standalone class I rolled that incorporates all of the functionality.
http://github.com/StlTenny/RestService
It executes the request as non-blocking, and returns the results in an easy to implement handler. Even comes with an example implementation.
Lets say I want to start the service on an event - onItemClicked() of a button. The Receiver mechanism would not work in that case because :-
a) I passed the Receiver to the service (as in Intent extra) from onItemClicked()
b) Activity moves to the background. In onPause() I set the receiver reference within the ResultReceiver to null to avoid leaking the Activity.
c) Activity gets destroyed.
d) Activity gets created again. However at this point the Service will not be able to make a callback to the Activity as that receiver reference is lost.
The mechanism of a limited broadcast or a PendingIntent seems to be more usefull in such scenarios- refer to Notify activity from service
Note that the solution from Robby Pond is somehow lacking: in this way you only allow todo one api call at a time since the IntentService only handles one intent at a time. Often you want to perform parallel api calls. If you want todo this you have to extend Service instead of IntentService and create your own thread.
Also when I hit the post(Config.getURL("login"), values) the app seems to pause for a while (seems weird - thought the idea behind a service was that it runs on a different thread!)
In this case its better to use asynctask, which runs on a different thread and return result back to the ui thread on completion.
Robby provides a great answer, though I can see you still looking for more information. I implemented REST api calls the easy BUT wrong way. It wasn't until watching this Google I/O video that I understood where I went wrong. It's not as simple as putting together an AsyncTask with a HttpUrlConnection get/put call.
There is another approach here which basically helps you to forget about the whole management of the requests. It is based on an async queue method and a callable/callback based response.
The main advantage is that by using this method you'll be able to make the whole process (request, get and parse response, sabe to db) completely transparent for you. Once you get the response code the work is already done. After that you just need to make a call to your db and you are done.
It helps as well with the problematic of what happens when your activity is not active.
What will happen here is that you'll have all your data saved in your local database but the response won't be processed by your activity, that's the ideal way.
I have an Activity calling a Service defined in IDownloaderService.aidl:
public class Downloader extends Activity {
IDownloaderService downloader = null;
// ...
In Downloader.onCreate(Bundle) I tried to bindService
Intent serviceIntent = new Intent(this, DownloaderService.class);
if (bindService(serviceIntent, sc, BIND_AUTO_CREATE)) {
// ...
and within the ServiceConnection object sc I did this
public void onServiceConnected(ComponentName name, IBinder service) {
Log.w("XXX", "onServiceConnected");
downloader = IDownloaderService.Stub.asInterface(service);
// ...
By adding all kinds of Log.xx I found that the code after if(bindService(...)) actually goes BEFORE ServiceConnection.onServiceConnected is being called - that is, when downloader is still null - which gets me into trouble. All the samples in ApiDemos avoid this timing problem by only calling services when triggered by user actions. But what should I do to right use this service after bindService succeeds? How can I wait for ServiceConnection.onServiceConnected being called reliably?
Another question related. Are all the event handlers: Activity.onCreate, any View.onClickListener.onClick, ServiceConnection.onServiceConnected, etc. actually called in the same thread (mentioned in the doc as the "main thread")? Are there interleaves between them, or Android would schedule all events come into being handled one-by-one? Or, When exactly is ServiceConnection.onServiceConnected actually going to be called? Upon completion of Activity.onCreate or sometime when A.oC is still running?
How can I wait for
ServiceConnection.onServiceConnected
being called reliably?
You don't. You exit out of onCreate() (or wherever you are binding) and you put you "needs the connection established" code in onServiceConnected().
Are all the event handlers:
Activity.onCreate, any
View.onClickListener.onClick,
ServiceConnection.onServiceConnected,
etc. actually called in the same
thread
Yes.
When exactly is
ServiceConnection.onServiceConnected
actually going to be called? Upon
completion of Activity.onCreate or
sometime when A.oC is still running?
Your bind request probably is not even going to start until after you leave onCreate(). Hence, onServiceConnected() will called sometime after you leave onCreate().
I had the same problem. I didn't want to put my bound service dependent code in onServiceConnected, though, because I wanted to bind/unbind with onStart and onStop, but I didn't want the code to run again every time the activity came back to the front. I only wanted it to run when the activity was first created.
I finally got over my onStart() tunnel vision and used a Boolean to indicate whether this was the first onServiceConnected run or not. That way, I can unbindService in onStop and bindService again in onStart without running all the start up stuff each time.
I ended up with something like this:
1) to give the auxiliary stuff some scope, I created an internal class. At least, the ugly internals are separated from the rest of the code. I needed a remote service doing something, therefore the word Something in class name
private RemoteSomethingHelper mRemoteSomethingHelper = new RemoteSomethingHelper();
class RemoteSomethingHelper {
//...
}
2) there are two things necessary to invoke a remote service method: the IBinder and the code to execute. Since we don't know which one becomes known first, we store them:
private ISomethingService mISomethingService;
private Runnable mActionRunnable;
Each time we write to one of these fileds, we invoke _startActionIfPossible():
private void _startActionIfPossible() {
if (mActionRunnable != null && mISomethingService != null) {
mActionRunnable.run();
mActionRunnable = null;
}
}
private void performAction(Runnable r) {
mActionRunnable = r;
_startActionIfPossible();
}
This, of course, assumes that the Runnable has access to mISomethingService, but this is true for runnables created within the methods of the RemoteSomethingHelper class.
It is really good that the ServiceConnection callbacks are called on the UI thread: if we are going to invoke the service methods from the main thread, we do not need to care about synchronization.
ISomethingService is, of course, defined via AIDL.
3) Instead of just passing arguments to methods, we create a Runnable that will invoke the method with these arguments later, when invocation is possible:
private boolean mServiceBound;
void startSomething(final String arg1) {
// ... starting the service ...
final String arg2 = ...;
performAction(new Runnable() {
#Override
public void run() {
try {
// arg1 and arg2 must be final!
mISomethingService.startSomething(arg1, arg2);
} catch (RemoteException e) {
e.printStackTrace();
}
}
});
}
4) finally, we get:
private RemoteSomethingHelper mRemoteSomethingHelper = new RemoteSomethingHelper();
class RemoteSomethingHelper {
private ISomethingService mISomethingService;
private Runnable mActionRunnable;
private boolean mServiceBound;
private void _startActionIfPossible() {
if (mActionRunnable != null && mISomethingService != null) {
mActionRunnable.run();
mActionRunnable = null;
}
}
private ServiceConnection mServiceConnection = new ServiceConnection() {
// the methods on this class are called from the main thread of your process.
#Override
public void onServiceDisconnected(ComponentName name) {
mISomethingService = null;
}
#Override
public void onServiceConnected(ComponentName name, IBinder service) {
mISomethingService = ISomethingService.Stub.asInterface(service);
_startActionIfPossible();
}
}
private void performAction(Runnable r) {
mActionRunnable = r;
_startActionIfPossible();
}
public void startSomething(final String arg1) {
Intent intent = new Intent(context.getApplicationContext(),SomethingService.class);
if (!mServiceBound) {
mServiceBound = context.getApplicationContext().bindService(intent, mServiceConnection, 0);
}
ComponentName cn = context.getApplicationContext().startService(intent);
final String arg2 = ...;
performAction(new Runnable() {
#Override
public void run() {
try {
mISomethingService.startSomething(arg1, arg2);
} catch (RemoteException e) {
e.printStackTrace();
}
}
});
}
}
context is a field in my class; in an Activity, you can define it as Context context=this;
I did not need queuing actions; if you do, you can implement it.
You likely will need a result callback in startSomething(); I did, but this is not shown in this code.
I did something similar before, the only different is I was not binding to service, but just starting it.
I would broadcast an intent from the service to notify the caller/activity about it is started.
I wanted to add some things you should or should not do:
bind the service not on create but onResume and unbind it onPause. Your app can go into pause (background) at any time by user interaction or OS-Screens.
Use a distinct try/catch for each and every service unbinding, receiver unregistering etc in onPause so if one is not bound or registered the exception doesn't prevent the others from being destroyed too.
I usually capsule binding in a public MyServiceBinder getService() Method. I also always use a blocking boolean variable so I don't have to keep an eye on all those calls using the servie in the activity.
Example:
boolean isBindingOngoing = false;
MyService.Binder serviceHelp = null;
ServiceConnection myServiceCon = null;
public MyService.Binder getMyService()
{
if(serviceHelp==null)
{
//don't bind multiple times
//guard against getting null on fist getMyService calls!
if(isBindingOngoing)return null;
isBindingOngoing = true;
myServiceCon = new ServiceConnection(
public void onServiceConnected(ComponentName cName, IBinder binder) {
serviceHelp = (MyService.Binder) binder;
//or using aidl: serviceHelp = MyService.Stub.AsInterface(binder);
isServiceBindingOngoing = false;
continueAfterServiceConnect(); //I use a method like this to continue
}
public void onServiceDisconnected(ComponentName className) {
serviceHelp = null;
}
);
bindService(serviceStartIntent,myServiceCon);
}
return serviceHelp;
}
Android 10 has introduced a new bindService method signature when binding to a service to provide an Executor (which can be created from the Executors).
/**
* Same as {#link #bindService(Intent, ServiceConnection, int)} with executor to control
* ServiceConnection callbacks.
* #param executor Callbacks on ServiceConnection will be called on executor. Must use same
* instance for the same instance of ServiceConnection.
*/
public boolean bindService(#RequiresPermission #NonNull Intent service,
#BindServiceFlags int flags, #NonNull #CallbackExecutor Executor executor,
#NonNull ServiceConnection conn) {
throw new RuntimeException("Not implemented. Must override in a subclass.");
}
This allows to bind to the service in a thread and wait until it is connected. E.g. stub:
private final AtomicBoolean connected = new AtomicBoolean()
private final Object lock = new Object();
...
private void myConnectMethod() {
// bind to service
ExecutorService executorService = Executors.newSingleThreadExecutor();
context.bindService(new Intent(context, MyServiceClass.class), Context.BIND_AUTO_CREATE, executorService, new
ServiceConnection() {
#Override
public void onServiceConnected(ComponentName name, IBinder binder) {
synchronized (lock) {
// TODO: store service instance for calls in case of AIDL or local services
connected.set(true);
lock.notify();
}
});
synchronized (lock) {
while (!connected.get()) {
try {
lock.wait();
} catch (InterruptedException e) {
throw new RuntimeException();
}
}
}
}
It is also necessary to run the service in a separate process:
<service
android:name=".MyServiceClass"
android:process=":service"
android:enabled="true"
android:exported="true" />
I figured out that these workarounds are only worth the effort and the wait only if your bound services are running in a different process than your application's main process.
For accessing data and methods in the same process (or application), I ended up implementing singleton classes. If the classes need a context for some methods, I leak the application context to the singleton classes. There is, of course, a bad consequence of it as it breaks the "instant run". But that is an overall better compromise, I think.
*The basic idea is same with #18446744073709551615, but I will share my code as well.
As a answer of main question,
But what should I do to right use this service after bindService succeeds?
[Original expectation (but not work)]
wait until service connected like below
#Override
protected void onStart() {
bindService(service, mWebServiceConnection, BIND_AUTO_CREATE);
synchronized (mLock) { mLock.wait(40000); }
// rest of the code continues here, which uses service stub interface
// ...
}
It won't work because both bindService() in onCreate()/onStart() and onServiceConnected() is called at same main thread.
onServiceConnected() is never called before wait finishes.
[Alternative solution]
Instead of "wait", define own Runnable to be called after Service Connected and execute this runnable after service connected.
Implement custom class of ServiceConnection as follows.
public class MyServiceConnection implements ServiceConnection {
private static final String TAG = MyServiceConnection.class.getSimpleName();
private Context mContext = null;
private IMyService mMyService = null;
private ArrayList<Runnable> runnableArrayList;
private Boolean isConnected = false;
public MyServiceConnection(Context context) {
mContext = context;
runnableArrayList = new ArrayList<>();
}
public IMyService getInterface() {
return mMyService;
}
#Override
public void onServiceConnected(ComponentName name, IBinder service) {
Log.v(TAG, "Connected Service: " + name);
mMyService = MyService.Stub.asInterface(service);
isConnected = true;
/* Execute runnables after Service connected */
for (Runnable action : runnableArrayList) {
action.run();
}
runnableArrayList.clear();
}
#Override
public void onServiceDisconnected(ComponentName name) {
try {
mMyService = null;
mContext.unbindService(this);
isConnected = false;
Log.v(TAG, "Disconnected Service: " + name);
} catch(Exception e) {
Log.e(TAG, e.toString());
}
}
public void executeAfterServiceConnected(Runnable action) {
Log.v(TAG, "executeAfterServiceConnected");
if(isConnected) {
Log.v(TAG, "Service already connected, execute now");
action.run();
} else {
// this action will be executed at the end of onServiceConnected method
Log.v(TAG, "Service not connected yet, execute later");
runnableArrayList.add(action);
}
}
}
And then use it in the following way (in your Activity class or etc),
private MyServiceConnection myServiceConnection = null;
#Override
protected void onStart() {
Log.d(TAG, "onStart");
super.onStart();
Intent serviceIntent = new Intent(getApplicationContext(), MyService.class);
startService(serviceIntent);
myServiceConnection = new MyServiceConnection(getApplicationContext());
bindService(serviceIntent, myServiceConnection, BIND_AUTO_CREATE);
// Instead of "wait" here, create callback which will be called after service is connected
myServiceConnection.executeAfterServiceConnected(new Runnable() {
#Override
public void run() {
// Rest of the code comes here.
// This runnable will be executed after service connected, so we can use service stub interface
IMyService myService = myServiceConnection.getInterface();
// ...
}
});
}
It worked for me. But there may be more better way.