RxAndroidBle long write - callback for each batch written - rxandroidble

Question

I'm doing a long write operation, sending 16 byte batches at a time. I'd like to have a progress bar show the progress of the long write to the user, so I need some sort of callback for each time a batch has been written.
From the documentation, it looked like setWriteOperationAckStrategy does this. However, when running the following code, I only end up seeing one message output to the log. What am I doing wrong here?
subscription = connection.flatMap(rxBleConnection -> rxBleConnection.createNewLongWriteBuilder()
.setCharacteristicUuid(uuid)
.setBytes(bytes)
.setMaxBatchSize(16)
.setWriteOperationAckStrategy(new RxBleConnection.WriteOperationAckStrategy() {
#Override
public Observable<Boolean> call(Observable<Boolean> booleanObservable) {
Log.d("TEST", "batch written");
return booleanObservable;
}
})
.build()

Answer 1

The setWriteOperationAckStrategy is similar to standard RxJava's Observable transformers. In order to keep the allocation low, we tend to modify source observable rather than to create a new one when each batch is completed.
subscription = connection.flatMap(rxBleConnection -> rxBleConnection.createNewLongWriteBuilder()
.setCharacteristicUuid(uuid)
.setBytes(bytes)
.setMaxBatchSize(16)
.setWriteOperationAckStrategy(new RxBleConnection.WriteOperationAckStrategy() {
#Override
public Observable<Boolean> call(Observable<Boolean> booleanObservable) {
Log.d("TEST", "batch written");
return booleanObservable
.doOnNext(new Action1<Boolean>() {
#Override
public void call(Boolean aBoolean) {
Log.d("TEST", "batch written");
}
});
}
})
.build()

Answer 2

I think this answer was for RxJava, for RxJava2 this is the updated lambda syntax:
.setWriteOperationAckStrategy(booleanObservable -> {
Log.d("TEST", "batch written");
return booleanObservable
.doOnNext(aBoolean -> {
Log.d("TEST", "batch written");
});
}
Full:
.setWriteOperationAckStrategy(new RxBleConnection.WriteOperationAckStrategy() {
#Override
public Observable<Boolean> apply(Observable<Boolean> booleanObservable) {
Log.d("TEST", "batch written");
return booleanObservable
.doOnNext(new Consumer<Boolean>() {
#Override
public void accept(Boolean aBoolean) {
Log.d("TEST", "batch written");
}
});
}