Services
Services
A service is a component that runs in the background to perform long-running operations without needing to interact with the user and it works even if application is destroyed. A service can essentially take two states
A service has life cycle callback methods that you can implement to monitor changes in the service's state and you can perform work at the appropriate stage. The following diagram on the left shows the life cycle when the service is created with startService() and the diagram on the right shows the life cycle when the service is created with bindService(): (image courtesy : android.com )
To create an service, you create a Java class that extends the Service base class or one of its existing subclasses. The Service base class defines various callback methods and the most important are given below. You don't need to implement all the callbacks methods. However, it's important that you understand each one and implement those that ensure your app behaves the way users expect.
| Sr.No. | Callback & Description |
|---|---|
| 1 | onStartCommand() The system calls this method when another component, such as an activity, requests that the service be started, by calling startService(). If you implement this method, it is your responsibility to stop the service when its work is done, by calling stopSelf() or stopService() methods. |
| 2 | onBind() The system calls this method when another component wants to bind with the service by calling bindService(). If you implement this method, you must provide an interface that clients use to communicate with the service, by returning an IBinder object. You must always implement this method, but if you don't want to allow binding, then you should return null. |
| 3 | onUnbind() The system calls this method when all clients have disconnected from a particular interface published by the service. |
| 4 | onRebind() The system calls this method when new clients have connected to the service, after it had previously been notified that all had disconnected in its onUnbind(Intent). |
| 5 | onCreate() The system calls this method when the service is first created using onStartCommand() or onBind(). This call is required to perform one-time set-up. |
| 6 | onDestroy() The system calls this method when the service is no longer used and is being destroyed. Your service should implement this to clean up any resources such as threads, registered listeners, receivers, etc. |