使用服务时ClassCastException

Question

I defined a local Service:

public class ComService extends Service implements IComService {
    private IBinder binder = new ComServiceBinder();

    public class ComServiceBinder extends Binder implements IComService.IServiceBinder {
        public IComService getService() {
            return ComService.this;
        }
    }

    public void test(String msg) {
        System.out.println(msg);
    }

    @Override
    public IBinder onBind(Intent intent) {
        return binder;
    }    
}

The corresponding interface:

public interface IComService {
    public void test(String msg);

    public interface IServiceBinder {
        IComService getService();
    }
}

Then i try to bind the service in another activity in another application, where the same interface is available:

bindService(new Intent("ch.ifi.csg.games4blue.gamebase.api.ComService"), conn, Context.BIND_AUTO_CREATE);

and

private ServiceConnection conn = new ServiceConnection() {
    @Override
    public void onServiceConnected(ComponentName name, IBinder service) {
        Log.i("INFO", "Service bound " + name);
        comService = ((IComService.IServiceBinder)service).getService();
        serviceHandler.sendEmptyMessage(0);
    }

    @Override
    public void onServiceDisconnected(ComponentName arg0) {
        Log.i("INFO", "Service Unbound ");
    }
};

but the line

comService = ((IComService.IServiceBinder)service).getService();

always throws a

05-02 22:12:55.922: ERROR/AndroidRuntime(622): java.lang.ClassCastException: android.os.BinderProxy

I can't explain why, I followed the app sample on http://developer.android.com/resources/samples/ApiDemos/src/com/example/android/apis/app/LocalServiceBinding.html

Any hints would be nice!

Answer 1

You need to use AIDL to define interfaces that span applications (so-called "remote services"). You followed a local binding example, but you are not using local binding. Try this and this sample project for a remote binding example using AIDL.