Hi all,
while doing the refactoring of the field handlers, and cleaning up in the SPI,
I did come across the subscription API again.
I have to admit I’m not that happy with it.
Right now you have to build a subscription request, and with the response to
that you can register a handler.
Every time I want to use the subscriptions, I have to dig again and find out
how to use things.
That means for me the API in its current state isn’t very intuitive.
Right now in order to subscribe you would do this:
final PlcSubscriptionRequest.Builder builder =
plcConnection.subscriptionRequestBuilder();
builder.addChangeOfStateField("value-1", “some-address”);
builder.addChangeOfStateField("value-2", “some-address”);
builder.addChangeOfStateField("value-3", “some-address”);
PlcSubscriptionRequest subscriptionRequest = builder.build();
// Execute the subscription response.
final PlcSubscriptionResponse subscriptionResponse =
subscriptionRequest.execute().get();
// Attach handlers for the incoming data.
for (String subscriptionName : subscriptionResponse.getFieldNames()) {
final PlcSubscriptionHandle subscriptionHandle =
subscriptionResponse.getSubscriptionHandle(subscriptionName);
subscriptionHandle.register(new ValueChangeHandler());
}
I would propose to change it that you provide the listener when creating the
subscription request:
final PlcSubscriptionRequest.Builder builder =
plcConnection.subscriptionRequestBuilder();
builder.addChangeOfStateField("value-1", “some-address”);
builder.addChangeOfStateField("value-2", “some-address”);
builder.addChangeOfStateField("value-3", “some-address”);
PlcSubscriptionRequest subscriptionRequest = builder.build(new
ValueChangeHandler());
// Execute the subscription response.
final PlcSubscriptionResponse subscriptionResponse =
subscriptionRequest.execute().get();
I know the main difference is that this way you would register the listener to
all fields and with the other one you have the chance to attach multiple
listners to different sets of fields. I would doubt that this use-case is very
common. And you could probably just do the sorting in the handler.
Another option would be to have two “build” methods … one which takes a
callback handler, and one that doesn’t … we could even just add the new build
method and leave the rest unchanged. This would allow both approaches.
What do you think?
Chris
