I am trying to create a module for Ignition to expose tag changes over a websocket to a custom-built client but none of the resources are up to date/exhaustive enough for 8.1.
Setting up the servlet was enough of a struggle just trying to figure out first how to add the servlet to the gateway, but then also what path that mapped out to (took a few articles here to figure out the path structure).
Once the socket was set up, I had to get the tag events. I saw on another discussion that a user was told to use the ManagedTagProvider class as it has replaced the previous SQLTags implementation which was marked as deprecated, however there is no functionality for reading a tag, getting a list of tags, or anything resembling a read operation for tags in that class. Which makes me wonder why it was suggested in the first place if the implementation is incomplete.
When that didn't work, I tried creating an ad-hoc FilteredTagChangeListener and subscribing to needed change events over the websocket looking like the following...
TagPath tag_path = TagPathParser.parse("default", path);
FilteredTagChangeListener listener = new FilteredTagChangeListener(tag_path,
EnumSet.of(FilteredTagChangeListener.TagChangeType.ValueChange),
new GatewayTagChangeListenerDelegate());
public class GatewayTagChangeListenerDelegate implements TagChangeListener {
@Override
public void tagChanged(TagChangeEvent tagChangeEvent) throws InvalidListenerException {
TagChangeEntity entity = new TagChangeEntity();
Gson gson = new Gson();
Logger logger;
entity.type = "change";
entity.tag_path = tagChangeEvent.getTagPath().toStringFull();
entity.value = tagChangeEvent.getValue().getValue();
logger = LogManager.getLogger(getClass());
logger.info("Subscribed tag change for tag \"" + entity.tag_path + "\". Value: " + entity.value.toString());
// More code for sending to subscribed clients
}
@Override
public boolean isLightweight() {
return TagChangeListener.super.isLightweight();
}
}
But I never get the trigger for the tag change. How are you supposed to do this in 8.1?