Why to use bound (not-started) services within the application process?

Question

As everyone might know, there are two primary types of services in Android: started and bound (I'm not counting started and bound services, as they're mostly the same as just started services).

You can find tons of tutorials on how to use bound services or how to bind to started service, but there are actually no answer on why would anyone use bound (not-started) services within the application process (in other words - without IPC)?

Is there any (hidden?) profit from using bound service (let's say for some sort of processing) over using standard threading tools (AsyncTaks, Executors, plain threads)? Would it worth boilerplate code for connection of such service?

Some context

Question appeared after digging through sources of Google Camera. They're creating a bound (once again - not-started) service for saving images. What is the point? Why not just used some Executor? Am I missing something important?

If that is a bound service, then there is no way it would help to persist saving progress while device configuration is changing (i.e. device is rotated). So I see no advantages.

Answer 1

Started Service is useful in case where there is need for no or very limited (one-way) interaction between starting component i.e. Activity or BroadcastReceiver, and the started service. For instance, a fire-and-forget background download. You give the downloader service a URL, start the service and forget all about it. The only way the downloader service ever interacts with the user is using Notifications. The Activity might as well go on the backstack in the meantime, you don't care. Note that in this case, the service is serving the Activity which started it, and there is no requirement for it to be available generically to other Activities.

On the other hand, bound service is a more generic service or one that needs to serve multiple activities, and more over, needs multiple bidirectional interactions i.e. Activity sends a message to Service, then Service sends a message back to Activity and so on. Consider the example of background music player service, where you pass the music file or remote stream URI/URL to the service, then another activity could change the volume or switch to another track etc. A message back from service to activity could be that the mp3 file is incomplete or corrupted, or a track completed message.

In fact, I came to this question looking for the answer to this exact question, but found the answer quite satisfactorily and complete in the link provided by @SagarPikhwal. Admittedly, I'm a newbie as far as Android programming is concerned, so the above is all as per what I understood !

Edit: Realized that I didn't answer (to the best of my abilities), the other part of the question about the code you saw for Google Camera. I think the reason why they create a bound service is because Camera is a common shared resource, and there could be multiple users of that system resource simultaneously. The activity using the camera service to capture an image or video is not the exclusive user. The Google Camera application is yet another user of the camera hardware, while there could others, and all of them served by the bound-service.