Android Service: onBind(Intent) and onUnbind(Inten

Question

I have the Activity and the Service. When Activity is started, it calls startService() to make this Service be alive even when Activity is destroyed, and bindService(), to communicate with this Service.

bindService() returns true, mService.onBind() is called, and ServiceConnection.onServiceConnected() is called too. All works.

When i destroy my Activity by pressing Back key, it calls unbindService(), and my mService.onUnbind() is called. (i return false in this onUnbind().)

Then i start this Activity again, bindService() returns true, and then mService.onBind() is NOT called! But ServiceConnection.onServiceConnected() is called too, and all works again.

It looks like Dalvik remembers what my onBind() returned last time, and just does not call onBind() again. When i destroy my Activity again, onUnbind() is NOT called too.

I can bind and unbind this Service to my Activity any number of times, but these methods will not be called anymore until I destroy Service by unbinding and calling stopService().

In docs i can't find any explanation of this behavior. Conversely, this figure shows that onBind() and onUnbind() should be called every time clients bind and unbind Service. This figure can be found on the bottom of this Dev Guide.

Answer 1

You can find it here: https://developer.android.com/guide/components/bound-services.html

You can connect multiple clients to a service simultaneously. However, the system caches the IBinder service communication channel. In other words, the system calls the service's onBind() method to generate the IBinder only when the first client binds. The system then delivers that same IBinder to all additional clients that bind to that same service, without calling onBind() again.

Answer 2

I think this (referenced from official dev guide) can explain all your queries:

Multiple clients can connect to the service at once. However, the system calls your service's onBind() method to retrieve the IBinder only when the first client binds. The system then delivers the same IBinder to any additional clients that bind, without calling onBind() again.