Pro Android with Kotlin

37
CHAPTER 4: Services
To actually perform the binding, you can proceed like for internal services. For example, 
inside an activity’s 
onCreate()
method, you could write the following:
val intent:Intent = Intent("
.START_SERVICE")
intent.setPackage("
")
bindService(intent, myConnection, Context.BIND_AUTO_CREATE)
Here, substitute the service package’s name for 
appropriately.
Now to send a message from the client to the service across the process boundary, you can 
write the following:
val msg = Message.obtain()
val bundle = Bundle()
bundle.putString("MyString", "A message to be sent")
msg.data = bundle
remoteSrvc?.send(msg)
Note that for this example you cannot add these lines into the activity’s 
onCreate()
method after the 
bindService()
statement because 
remoteSrvc
gets a value only after the 
connection fires up. But you could, for example, add it to the 
onServiceConnected()
method 
of the 
ServiceConnection
class.
Note
In the previous code, no precautions were taken to ensure connection sanity. You should add 
sanity checks for productive code. Also, unbind from the service inside the 
onStop()
method.
Data Sent by Services
Up to now we were talking of messages sent from the service client to the service. Sending 
data in the opposite direction, from the service to the service client, is possible as well; it can 
best be achieved by using an extra 
Messenger
inside the client, a broadcast message, or a 
ResultReceiver
class.
For the first method, provide another 
Handler
and 
Messenger
in the service client, and once 
the client receives an 
onServiceConnected()
callback, send a 
Message
to the service with the 
second 
Messenger
passed by the 
replyTo
parameter.
internal class InHandler(val ctx: Context) : Handler() {
override
fun handleMessage(msg: Message) {
// do something with the message from the service
}
}
class MainActivity : AppCompatActivity() {
private var remoteSrvc:Messenger? = null
private var backData:Messenger? = null

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