How to implement the communication between a Service and an Activity in different processes?

Question

I read some similar questions (for example at this link), but the problem I'm asking is a bit different. In fact, in my case the service is started manually by the startService method, then as a consequence it can not be started using the bindService method.

1. Suppose we have a package that contains the MainService service and MainServiceActivity activity. In the file "AndroidManifest.xml" this activity is declared with action MAIN and category LAUNCHER. This activity is used to configure the service via the SharedPreferences and start the service by invoking startService method. In other words, typically the user launches the MainServiceActivity and configures/starts the MainService.
2. Now consider another activity (Let's call it SecondActivity) that is part of another package. Depending on the configuration, the service starts this activity using the startActivity method, so this other activity is running on a separate process than the MainService. As soon as the activity is running, it should inform the service.
3. At this point, a communication request/reply begins between the MainService and the SecondActivity: the service sends a request and the activity sends a reply.

The communication via messaging might fit, but the MainService is started through startService method, so the bindService method can not be invoked by activities that want to bind to the service.

Then I had an idea that makes use of an additional service (Let's call it UtilityService), which is part of the same package of MainService: the UtilityService could be started using the bindService method. As a consequence:

• as soon as the MainService is running, it might perform the bind to the UtilityService;
• when the MainService launches an external activity (for example the above SecondActivity), this activity bind to the UtilityService.

In this way, both the MainService and the SecondActivity are connected to the UtilityService, where the latter acts as an intermediary for communication.

Are there alternatives to this idea?

Answer 1

In fact, in my case the service is started manually by the startService method, then as a consequence it can not be started using the bindService method.

You can both bind and start a service, if you wish. It's a bit unusual, but it can be done.

Are there alternatives to this idea?

Binding has nothing in particular to do with services being able to communicate with activities. Using some sort of callback or listener object via binding is a possibility, but it is far from the only one.

You can:

• Have the service send a broadcast Intent, to be picked up by the activity

• Have the activity send a PendingIntent (e.g., via createPendingResult()) to the service in an Intent extra on the command sent via startService(), to be used by the service to send information back to the activity (or wherever the activity wants it to go, such as a broadcast)

• Have the activity pass a Messenger tied to its Handler to the service in an Intent extra on the command sent via startService(), to be used by the service to send information back to the activity

All of those work perfectly well between processes, as well as within a process.