@Override
                    public void onReceive(Context context, Intent intent) {
                        int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, -1);
                        BleAdapterState internalState = mapToBleAdapterState(state);
                        RxBleLog.i("Adapter state changed: %s", internalState);
                        emitter.onNext(internalState);
                    }
Observes Bluetooth adapter state. This responds to user interactions as well as system controlled state changes.
<p>
NOTE: Make sure that this Observable is unsubscribed according to the Activity lifecycle. It internally uses BroadcastReceiver, so
it is required that it us unregistered before onDestroy.
rxandroidble/src/main/java/com/polidea/rxandroidble2/RxBleAdapterStateObservable.java