Introducing Service and IntentService

If the basic unit of a visible application is Activity, its equivalent unit for non-visible components is Service. Just like activities, services must be declared in the AndroidManifest file so that the system is aware of them and can manage them for us.

<service android:name=".MyService"/>

Service has lifecycle callback methods similar to those of Activity, which are always invoked on the application's main thread.

Also, just like Activity, Service does not automatically entail a separate background thread or process, and performing intensive or blocking operations in a Service callback method can lead to an Application Not Responding dialog.

However, there are several ways in which services are different to activities, listed as follows:

• A Service does not provide a user interface

• There can be many services active at the same time within an application

• A Service can remain active even if the application hosting it is not the current foreground application...