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→Bound Service
== Bound Service ==
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A bound service is similar to a started service with the exception that a started service does not generally return results or permit interaction with the component that launched it. A bound service, on the other hand, allows the launching component to interact with, and receive results from, the service. Through the implementation of interprocess communication (IPC), this interaction can also take place across process boundaries. An activity might, for example, start a service to handle audio playback. The activity will, in all probability, include a user interface providing controls to the user for the purpose of pausing playback or skipping to the next track. Similarly, the service will quite likely need to communicate information to the calling activity to indicate that the current audio track has completed and to provide details of the next track that is about to start playing.
A bound service must include an implementation of the onBind() method which is called both when the service is initially created and when other clients subsequently bind to the running service. The purpose of this method is to return to binding clients an object of type IBinder containing the information needed by the client to communicate with the service.
In terms of implementing the communication between a client and a bound service, the recommended technique depends on whether the client and service reside in the same or different processes and whether or not the service is private to the client. Local communication can be achieved by extending the Binder class and returning an instance from the onBind() method. Interprocess communication, on the other hand, requires Messenger and Handler implementation. Details of both of these approaches will be covered in later chapters.
== The Anatomy of a Service ==
