How to properly asychronously load UI component using Event Queues in ZK framework?

Question

I have a custom composer/controller class that extends GenericForwardComposer. Inside this class I have some methods that are being used to initialize UI components with data. This is a very long operation and takes time to complete. Due to performance issues I am trying to asynchronously load this data using Event Queues. This way it will not block users from accessing other functions while the process runs in the background.

In my custom class there is an init method that starts the processing. This method invokes several other methods that handle the majority of the work.

My thinking was that I can use Event Queues something as such:

public class MyWidgetController extends GenericForwardComposer
{

    public void init(final Component comp)
    { 
          //other method logic ...
          EventQueue queue = EventQueues.lookup("myQueue", EventQueues.SESSION, true); 
          queue.subscribe(this); //not sure
          queue.publish(new Event("onInitPrimaryLoad", componentA, ""));
          queue.publish(new Event("onInitSecondaryLoad", componentB, ""));
      }

    @ViewEvent(componentID = "componentA", eventName = "onInitPrimaryLoad")
    public void onInitPrimary( final Event event){ //logic }

    @ViewEvent(componentID = "componentB", eventName = "onInitSecondaryLoad")
    public void onInitSecondary( final Event event){ //logic }

    //other class methods…
}

Not sure if this is all correct. Don't really need a callback method as the Events (publish) themselves are loading the UI components with data. The application runs with no issue but I'm not sure if I'm implementing this correctly.

Any advice or corrections are appreciated

Answer 1

The @ViewEvent seems to be Hybris specific and is not part of the ZK framework, that's why I can't comment on it.

Your example doesn't do async processing at all, the events are published into the current thread and the ui will block and only return after all these events have been processed. (even worse using a SESSION scoped event queue the events are published into all desktops (roughly browser tabs) of that user - most likely executing your heavy work multiple times. You should use a DESKTOP scoped event queue instead.

Also I don't fully understand why you don't need a callback ... when doing async processing you always need some kind of callback or create a thread manually.

Especially in ZK it is vital to perform the heavy work in a separate thread. Once the data is retrieved lock the UI as short as possible to perform updates to the component tree or component models - this keeps the UI as responsive to the user as possible.

The EventQueue usage is described in the official docs.

Based on those I create 2 runnable examples illustrating the simplified and the more generic approach.

As an alternative you can activate/deactivate a ZK desktop directly without using event queues as in this (my preferred) example.