Pro Android with Kotlin

38
CHAPTER 4: Services
private val myConn = object : ServiceConnection {
override
fun onServiceConnected(className: ComponentName,
service: IBinder) {
remoteSrvc = Messenger(service)
backData = Messenger(
InHandler(this@MainActivity))
// establish backchannel
val msg0 = Message.obtain()
msg0.replyTo = backData
remoteSrvc?.send(msg0)
// handle forward (client -> service)
// connectivity...
}
override
fun onServiceDisconnected(clazz: ComponentName) {
remoteSrvc = null
}
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// bind to the service, use ID from the manifest!
val intent = Intent("
.START_SERVICE")
intent.setPackage("
")
val flags = Context.BIND_AUTO_CREATE
bindService(intent, myConn, flags)
}
}
The service can then use this message, extract the replyTo attribute, and use it to send 
messages to the service client.
internal class IncomingHandler(val ctx: Context) :
Handler() {
override
fun handleMessage(msg: Message) {
val s = msg.data.getString("MyString")
val repl = msg.replyTo
Toast.makeText(ctx, s, Toast.LENGTH_SHORT).show()
Log.e("IncomingHandler", "!!! " + s)
Log.e("IncomingHandler", "!!! replyTo = " + repl)
// If not null, we can now use the 'repl' to send
// messages to the client. Of course we can save
// it elsewhere and use it later as well
if(repl != null) {
val thr = Thread( object : Runnable {

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39
CHAPTER 4: Services
override fun run() {
Thread.sleep(3000)
val msg = Message.obtain()
val bundle = Bundle()
bundle.putString("MyString",
"A reply message to be sent")
msg.data = bundle
repl?.send(msg)
}
} )
thr.start()
}
}
}
The other two methods, using a broadcast message or a ResultReceiver class, get handled 
in Chapters 
5
 and 
12
.
Service Subclasses
Up to now we were always using android.app.Service as a base class for services we 
described. There are other classes supplied by Android that are usable as base classes, 
though, with different semantics. For Android 8.0, there are no less than 20 service classes 
or base classes you can use. You can see them all in the Android API documentation in the 
“Known Direct Subclasses” section.
Note At the time of writing this book, you can find this documentation at 
https://developer.
android.com/reference/android/app/Service.html
.
The most important service classes are the following three:

android.app.Service: This is the one we’ve been using so far. This 
is the most basic service class. Unless you use multithreading inside 
the service class or the service is explicitly configured to execute in 
another process, the service will be running inside the service caller’s 
main thread. If this is the GUI thread and you don’t expect the service 
invocation to run really fast, it is strongly recommended you send 
service activities to a background thread.

android.app.IntentService: While a service by design does not 
naturally handle incoming start requests simultaneously to the 
main thread, an IntentService uses a dedicated worker thread 
to receive multiple start messages. Still, it uses just one thread to 
work with start requests, so they get executed one after the other. 
IntentService classes take care of correctly stopping services, so 
you don’t need to care about this yourself. You have to provide the 
service’s work to be done for each start request inside an overwritten 

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