When creating android applications, that are not trivial, it is important to keep in mind that android activities, widgets, and services have somewhat autonomous lifecycles that are controlled by the operating system itself. This is profound impacts on how you have to think about applications, since there will no longer something unified, but rather are a lot of different parts that are being orchestrated somewhat randomly. For example, applications process can be terminated anytime, or its activities can be terminated, or its services can be restarted. If you do not plan for such diversity in lifecycle states when building each widget service or activity, you will have a really tough time syncing them all up in the final application.

Android applications run in a native Linux process, in the underlying Linux OS. This process houses activities (screens), widgets, and services (non visual long running application parts). When working with Android apps, it is important to remember to keep long running code running in threads that are not tied to the main thread or event dispatch thread, in order to get an “application not responding” error. A common mistake that is made is long running tasks are performed in this EDT/main thread, and this leads to lots of application failures.

This tutorial will show you how to create a simple service, that does not use IPC (inter process communication). Services are great for running long running tasks and business logic, outside an Activity, which is tied to the user interface. For example, if you have a background task that has to download data periodically, then you should put that task in a Service. You can explicitly start a service and stop it as well. With IPC you can connect to a running service and call methods on it, however, in this example, I won’t be using any IPC; instead all data transfer will happen via a shared object and a listener.