ZK Developer's Guide/Advanced ZK/Long Operations/Alternative 4: Piggyback (No Suspend or Resume, No Timer)

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Instead of checking the results periodically, you can piggyback them to the client when the user, say, clicks a button or enters something.

To piggyback, all you need to do is to register an event listener for the onPiggyback event to one of the root components. Then, the listener will be invoked each time ZK Update Engine has processed the events. For example, you can rewrite the codes as follows.

<window id="main" title="Working Thread3" onPiggyback="checkResult()">
    <zscript>
     List result = Collections.synchronizedList(new LinkedList());
 
     void checkResult() {
         while (!result.isEmpty())
             main.appendChild(result.remove(0));
     }
    </zscript>
    <timer id="timer" />
    <button label="Start Working Thread">
        <attribute name="onClick">
     		timer.start();
     		new test.WorkingThread2(desktop, result).start();
        </attribute>
    </button>
</window>

The advantage of the piggyback is no extra traffic between the client and the server. However, the user sees no updates if he doesn't have any activity, such as clicking or typing. Whether it is proper is really up to the application requirements.

Note: A deferrable event won't be sent to the client immediately, so the onPiggyback event is triggered only if a non-deferrable event is fired. Refer to the Deferrable Event Listeners section.