Is using Parcelable the right way to send data between applications?

Question

I am trying to understand how to communicate between applications in Android - not just between Activity instances.

I set up a \'client\' that sends a Messe

Answer 1

If you dont want to use a persistence layer somewhere ( i use cloud apis ) you could run a service in a separate process and bind to the service the respective apps that need the shared value-holder type object data. the service would be where you construct and get the obj values on behalf of connecting ( binding ) apps.

Answer 2

You cannot unmarshall a class at a process that has no knowledge of this class (as you already correctly pointed out). If you want MyParcelable to be sent to your Service, then you need to include MyParcelable in the Service at build, and include the right ClassLoader to be used when unmarshalling, because unmarshalling is done by a system thread, which doesn't know what MyParcelable is even if you included it at compile time.

EDIT:

(a) include MyParcelable into 2 different pkgs and have them be seen as the same class

Make a library of your common classes and include it in both applications (the application and the Service). You can either mark it as an Android library (in Eclipse this is right under the project's Android properties) or export it as a JAR and import it in both apps. It's always a good idea to have independent classes in a library instead of putting them in the apps directly. This way you can reuse them on other projects ;)

(2) include the right ClassLoader (where do I get the right class loader from, for example)

You can get your ClassLoader from the current thread when you're executing your code. Obviously this ClassLoader knows about your classes because it's executing your code ;) For example in Activity#onCreate(), you can do Thread.currentThread.getContextClassLoader(). Since your MyParcelable class is also included on the Service, you can do the same to get a valid ClassLoader to unmarshall.

Another solution for IPC is to define an AIDL interface so you don't have to implement Parcelable.

Answer 3

OK, I found the 'easy way' I was looking for. You can put a Bundle into the Message.obj field. Bundle is Parcelable so can be transported between client and server. There's no issue of the server not knowing what class it's receiving as Bundle is 'built into' Android Java. And Bundle can apparently include 'sub-Bundles' with in. This is simpler than having to deal with ensuring both parties know the definition of a user-defined class. Thanks for the answers above - I certainly appreciated the info!