Question

I wrote an android program that: has a main activity for UI, and it starts a service. The service timely callbacks the UI activity to update views. It works fine except: if the activity is closed (with BACK) and start again, the service will also be started again (The service plays audio file, so there are two overlapped sounds).
I use bindService with BIND_AUTO_CREATE flag to start and connect to service. According to the document, it should create service only if it doesn’t exist, but obviously it starts another instance when opened second time.
All I want is when the activity is closed, the service goes on running, and when the activity opens again, it can reconnect to the service. Is that possible? Or I just misunderstand the usage of service?

Tried more:
Use ICountService (described in .aidl) instead of CountService in bindService Intent. It’s onDestroyed is called when the activity is closed.

Below is code of service creating if it helps.

    ServiceConnection conn = new ServiceConnection(){
    @Override
    public void onServiceConnected(ComponentName c, IBinder b) {
        Log.d("TK","Connected");
        //binder = (ICountService.Stub) b;
        service = ICountService.Stub.asInterface(b);
        try {
            service.setCallback(new ICountCallback.Stub(){

                @Override
                public void alert() {
                    Log.d("TK","alert!");
                }

                @Override
                public void updateTime(final int sec) {
                    handler.post(new Runnable(){

                        @Override
                        public void run() {
                                                            indicator.setText(toText(sec));
                        }

                    });
                }               
            });
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void onServiceDisconnected(ComponentName c) {
        Log.d("TK","Disconnected");
    }           
};

private void startCountService(){
    Intent i = new Intent(ICountService.class.getName());
    boolean ok = context.bindService(i, conn, Context.BIND_AUTO_CREATE);
    Log.d("TK", "bindService="+ok);
}

Answer 1

According to the document, it should create service only if it doesn’t exist, but obviously it starts another instance when opened second time.

bindService() will create the service instance if the service is not running. unbindService() will destroy the service instance if there are no other bound connections and nobody called startService(). If the service is destroyed on unbindService(), then a subsequent bindService() will create a new service instance.

IMHO, ideally, unbindService() would not immediately destroy the service, but let it linger for a few seconds first, in case there is a bindService() shortly after the unbindService(). However, that is not how they implemented it.

All I want is when the activity is closed, the service goes on running, and when the activity opens again, it can reconnect to the service.

You should be using startService() and stopService() instead of (or conceivably in addition to) bindService() and unbindService().