Background Service

A simple android project that demonstrates how to implement background service.

Android Services

• A service is a android application component that executes the task in the background without effecting the users current activity.
• No user interface is required
• By Default service runs on Main UI thread (Does not run separate thread or process)
• ContextWrapper class is super class of Service, Context is super class of ContextWrapper

Output

Main UI Thread:

• When we create an android application, the android system will create a default process, i’e default thread is created, This default thread is called as Main Thread or UI thread.
• All the components (Activities, Services, Broadcast Receivers & Services) runs on the same thread that is Main UI thread.
• Apart from the Main thread if we create any thread that we can call it as Background thread or Worker Thread.
• On Main UI thread we can only perform small operations like UI operations, Small Animations, Mathematical or Logical operations.
• Worker thread or Background thread are used to perform long running operations like Upload or Download File, Playing music, Heavy database queries & Network operations.

Service Types:

• Started Service ( 1. Foreground Service, 2. Background Service)
• Bound Service
• Intent Service

Started Service:

• Started service basically can started by android components like Activity, Broadcast Receiver, Content Provider, Services
• When service started can run in background indefinitely, Even the component that started is also destroyed
• There is always one way communication in case of started service
• startservice()is used to start service & stopservice() or stopself() are used to stop service.
• Runs on Main Ui thread

Bound Service

• A bound service allows the components (Activities, Services & Content providers) to bind to the service.
• This service exists as long as the there is at least one component bound to it.
• When all the calling components destroyed then the service also destroyed.
• By default it has two communication.
• bindservice() is used to start service & unbindservice() or stopself() are used to stop service.
• Runs on Main Ui thread

Foreground Service

• This service is always uses the notification to notify the user that some background operation is going on (Such as Play Music, Download files)
• Foreground service is always noticeable to user, That is the user aware of foreground service. Runs on Main UI thread.

Background Service

• This Service is not noticeable to the user & this is used to perform some background operations such as Sending email, Receiving whatsapp messages.
• Runs on Main UI thread.

Intent Service

• This service is advanced form of background service.
• This is Subclass of Service.
• It uses Worker Thread or Background thread by default to perform long running operations, So it runs
• Use startService() to start service and it stops automatically when task is done.
• It executes one task at a time, If you assign multiple tasks to the same intent service, Then the task will be arranged in - the queue. It handles multi threading internally and saves memory
• onHandleIntent() is default override method in case of Intent Service.
• onStartCommand() method implemented internally & onCreate(), onDestroy(), onBind() are optional

Service Lifecycle

How to stop Intent Service:

• Incase of intent service it does not stop or accept new requests through the same intent until it completes its onHandleIntent() competes the previous request.
• If we try to start again same intent-service with same other actions, onHandleIntent() will only called only after when previous request finished. -Also startservice() or stopSelf() won’t work until onHandleIntent() finishes its task.
• Declare the service as a separate process in the manifest & And when you want to stop its execution, just kill that process.

How to send Data to services

• We can send data to service using intent
• There is no default mechanism to return results back from the background service.
• We can use Broadcast receiver to communicate with the service or Intent Service

Security concerns

• Your service should always be accessible within your own application, Use the following attribute to access only from your app- android:exported:”false"
• Use explicit intent to start service.
• Use LoacalBroadcastReciever to communicate with service (LocalBroadcastManager.getInstance(this).registerReceiver())

Limitations

• Background app cannot use the Intent Service, Only foreground app can only use intent service from Oreo version
• Why such restrictions: Background services consumes more memory, which leads to battery drains.

JobIntent Service

• Modern way to run background service
• It works in all devices (Api > 14)
• It internally uses Job scheduler api.
• It requires WAKE_LOCK & BIND_JOB_SERVICE permissions
• onHandleWork() is default override method.
• It Runs on worker Thread or Background thread.