pramanj said

pramanj said

In order to subscribe to multiple items the client sdk documentation says “You can add a notification listener either to the subscription or to each item (above). The latter will provide you more detailed information on the data changes, but creating the listener to the subscription can be easier to use and more light-weight. The SampleConsoleClient demonstrates both, but uses mainly the item based listener.”

I am unable to see corresponding listener code in the sample. Is it that the same listener will be triggered for any item change in the subscription of multiple items? Willl it not be inefficient that way if all items change every specified minimum interval? All items will be sent one by one to the listener?` Will a read on group of items from client not be efficient instead of subscription if all values change every cycle?

Some clarification will be appreciated?

PRAMANJ

In other words, how to create listener to subscription rather than to individual items?
regards
PRAMANJ

Got it , its subscriptionListener that I have to see. Pl ignore my previous message.
regards
PRAMANJ

Some more clarifications:

1. If you add an already existing item to a subscription , what happens? Does it get ignored or added twice in the list?
2. To add a new item to a subscription, do we have to necessarily pause or suspend the subscription? What happens if we try to add an item to a subscription without pausing it?
3. In the sampleConsoleClient application, once we subscribe to an item, the menu displays only p for pause, i for change interval etc, we cannot do anything else like write/read an item value while in subscribe mode. Why so?
4. Once we pause the subscription, we cannot resume subscription without adding a new item to subscription! Suppose I want to resume subscription without adding new item in the subscription list, how do I do it?

regards
PRAMANJ

Heikki Tahvanainen said

1. In SampleConsoleClient, the existing item is ignored. If you just call

sub.addItem(item);

then the SDK will add the new item twice. However, in the SampleConsoleClient you can see an example of how to check if this subscription already contain this item before adding it. This is done with

sub.hasItem(nodeId, attributeId);

2. You do not need to do anything special before adding a new item to a subscription. The pausing is functionality of SampleConsoleClient. It is made because the usage of command line application is easier this way. In SampleConsoleClient source, you will see that pausing means setting subscription.setPublishingEnabled(false).

3. SampleConsoleClient is meant to function as an example application presenting how to use the SDK. It is also intended to be used from command line. When subscriptions are enabled, there might be a lot of data being printed to the command line. Other command line prints and user input might be lost among these other lines.

4. Subscribe again to one of the items that you are already subscribed to. The new item will be ignored and you will see the subscription menu.

1. Ok got it. But if we add an item twice , will it generate two calls to listener functions? Of course it depends on the server how it will take care of this functionality.
2. Ok. I understand that pausing is done by setting “subscription.setPublishingEnabled(false) “, but I wanted to clarify if its OK if we add items in subscription list without pausing subscription. In the sample client application this is done after pausing so I got confused. But I guess its only to stops the prints on console from subscriptions to avoid mixup if Inputs and outputs.
3. As above, and its clear.
4. Ok got it. Its related to the above question only, but we have to necessarily select another (same) item to proceed in the sample application, but not mandatory to pause in our implementation.

Thanks a lot
Regards
PRAMANJ

Ok thanks for the clarification. But I don’t know the point behind accepting same item multiple times in the same subscription! That’s something for specification to state. Of course there is a way provided to prevent multiple item addition for us to ensure unique items only. Of course if same item is added multiple times the server will blindly generate events for both entries! Its doesn’t know or care if the item already exists!

regards
PRAMANJ

In the sampleConsoleApplication , if we subscribe to a node followed by “/*” then all nodes below this hierarchy are subscribed to. But if we have multiple folders below this folder, will all the nodes below it be subscribed recursively? I am lazy to create such as hierarchy and test.

How does the subscription work in client?

Regards
PRAMANJ