Package org.zkoss.zk.ui.event.impl

Class DesktopEventQueue<T extends Event>

java.lang.Object
org.zkoss.zk.ui.event.impl.DesktopEventQueue<T>
All Implemented Interfaces:
Serializable, EventQueue<T>
public class DesktopEventQueue<T extends Event> extends Object implements EventQueue<T>, Serializable
The default implementation of the desktop-scoped event queue (EventQueue).
Since:
5.0.0
Author:
tomyeh
See Also:

  • Constructor Details

    • DesktopEventQueue

      public DesktopEventQueue()

  • Method Details

    • isIdle

      public boolean isIdle()
      Returns if there is listener being registered.

    • publish

      public void publish(T event)
      Description copied from interface: EventQueue
      Publishes an event to the queue.

      If the scope of a event queue is desktop or group, this method must be called within an activated execution (i.e., Executions.getCurrent() not null), or in an asynchronous listener (see EventQueue).

      On the other hand, if the scope is session or application, it is OK to be called without the current execution.

      Specified by:
      publish in interface EventQueue<T extends Event>
      Parameters:
      event - the event to publish.
      Notice that all subscribers will receive the event no matter what the event's name and target are.
      You could publish an anonymous event by publish(new Event("", null, data)).

    • subscribe

      public void subscribe(EventListener<T> listener)
      Description copied from interface: EventQueue
      Subscribes a listener to this queue. It is the same as subscribe(listener, false) (EventQueue.subscribe(EventListener,boolean). In other words, it subscribes a synchronous listener.

      Note: this method must be called within an activated execution (i.e., Executions.getCurrent() not null), no matter what scope the event queue is.

      Note: the listener could access the component associated with the event (Event.getTarget()), only if this is an EventQueues.DESKTOP event queue.

      An event listener can be subscribed multiple times, and it will be invoked multiple times if an event is published.

      Even if this is a EventQueues.GROUP, EventQueues.SESSION, or EventQueues.APPLICATION event queue, the listener is subscribed for the current desktop only, i.e., it can only access the components belong to the subscribed desktop. If you want to use the same listener to manipulate multiple desktops, you have to subscribe them separately when the corresponding execution is available.

      Specified by:
      subscribe in interface EventQueue<T extends Event>
      See Also:

    • subscribe

      public void subscribe(EventListener<T> listener, EventListener<T> callback)
      Description copied from interface: EventQueue
      Subscribes a synchronous or asynchronous listener to this event queue. A synchronous listener works the same as a normal event listener, while an asynchronous listener is executed asynchronously in an working thread. Refer here for details.

      Here is an example, 

      
        <window title="long operation" border="normal">
        <zscript>
        void print(String msg) {
                new Label(msg).setParent(inf);
        }
        </zscript>
        <button label="async long op">
                <attribute name="onClick"><![CDATA[
        if (EventQueues.exists("longop")) {
         print("It is busy. Please wait");
         return; //busy
        }
        
        EventQueue eq = EventQueues.lookup("longop"); //create a queue
        String result;
        
        //subscribe async listener to handle long operation
        eq.subscribe(new EventListener() {
         public void onEvent(Event evt) { //asynchronous
           org.zkoss.lang.Threads.sleep(3000); //simulate a long operation
           result = "success"; //store the result
         }
        }, new EventListener() { //callback
         public void onEvent(Event evt) {
           print(result); //show the result to the browser
           EventQueues.remove("longop");
         }
        });
        
        print("Wait for 3 seconds");
        eq.publish(new Event("whatever")); //kick off the long operation
                ]]></attribute>
        </button>
        <vbox id="inf"/>
        </window>

      Notice that, though an asynchronous listener cannot access the desktop and has no current execution, it can invoke EventQueue.publish(T) to publish the events. Refer to another example in EventQueue.subscribe(EventListener,boolean).

      Specified by:
      subscribe in interface EventQueue<T extends Event>
      Parameters:
      listener - the asynchronous listener to invoke when an event is received
      callback - the callback listener, which will be invoked if the asynchronous listen has been invoked. Unlike the asynchronous listener, the callback listener works like a normal listener. You can access the current execution, and update the desktop.
      Version Difference: since 5.0.8, the event argument is the same as the one passed to listener. In the prior version, it is always null for the callback listener.
      See Also:

    • subscribe

      public void subscribe(EventListener<T> listener, boolean async)
      Description copied from interface: EventQueue
      Subscribes a synchronous or asynchronous listener to this event queue. A synchronous listener works the same as a normal event listener, while an asynchronous listener is executed asynchronously in an working thread. Refer here for details.

      The use of synchronous listeners is straightforward -- they are just the same a normal event listener. Here is an example of using an asynchronous listener. In this example, we use an asynchronous listener to execute a long operation, a synchronous listener to update the desktop, and they communicate with each other with events.

      There is another way to do the same job, callback, refer to EventQueue.subscribe(EventListener,EventListener) for example. 

      
        <window title="long operation" border="normal">
        <zscript>
        void print(String msg) {
        new Label(msg).setParent(inf);
        }
        </zscript>
        <button label="async long op">
        <attribute name="onClick"><![CDATA[
        if (EventQueues.exists("longop")) {
         print("It is busy. Please wait");
         return; //busy
        }
        
        EventQueue eq = EventQueues.lookup("longop"); //create a queue
        String result;
        
        //subscribe async listener to handle long operation
        eq.subscribe(new EventListener() {
         public void onEvent(Event evt) {
           if ("doLongOp".equals(evt.getName())) {
             org.zkoss.lang.Threads.sleep(3000); //simulate a long operation
             result = "success"; //store the result
             eq.publish(new Event("endLongOp")); //notify it is done
           }
         }
        }, true); //asynchronous
        
        //subscribe a normal listener to show the result to the browser
        eq.subscribe(new EventListener() {
         public void onEvent(Event evt) {
           if ("endLongOp".equals(evt.getName())) {
             print(result); //show the result to the browser
             EventQueues.remove("longop");
           }
         }
        }); //synchronous
        
        print("Wait for 3 seconds");
        eq.publish(new Event("doLongOp")); //kick off the long operation
        ]]></attribute>
        </button>
        <vbox id="inf"/>
        </window>

      The asynchronous event listener requires Server Push (ServerPush).

      If you want to show a busy message to cover a portion of the desktop, use Clients.showBusy(org.zkoss.zk.ui.Component,String)

      Note: this method must be called within an activated execution, i.e., Executions.getCurrent() not null.

      An event listener can be subscribed multiple times, and it will be invoked multiple times if an event is published.

      Even if this is an application-level or session-level event queue, the listener is subscribed for the current desktop only. If you want to use the same listener for multiple desktops, you have to subscribe them separately when the corresponding execution is available.

      Specified by:
      subscribe in interface EventQueue<T extends Event>
      Parameters:
      listener - the listener
      async - whether the listener is asynchronous
      See Also:

    • unsubscribe

      public boolean unsubscribe(EventListener<T> listener)
      Description copied from interface: EventQueue
      Unsubscribes a listener from the queue.

      Note: this method must be called within an activated execution, i.e., Executions.getCurrent() not null.

      Notice that this method only unsubscribes the listener subscribed for this desktop. It doesn't check the listeners for other desktops even if this is an application-level or session-level event queue.

      Specified by:
      unsubscribe in interface EventQueue<T extends Event>
      Returns:
      true if the listener was subscribed.

    • isSubscribed

      public boolean isSubscribed(EventListener<T> listener)
      Description copied from interface: EventQueue
      Returns if an event listener is subscribed.

      Notice that this method only checks the listeners subscribed for this desktop. It doesn't check the listeners for other desktops even if this is an application-level or session-level event queue.

      Specified by:
      isSubscribed in interface EventQueue<T extends Event>

    • close

      public void close()
      Description copied from interface: EventQueue
      Closes the event queue. After closed, application cannot access any of its method.

      Don't call this method directly. It is called only internally. Rather, use EventQueues.remove(java.lang.String) instead.

      Specified by:
      close in interface EventQueue<T extends Event>

    • isClose

      public boolean isClose()
      Description copied from interface: EventQueue
      Returns whether it is closed.
      Specified by:
      isClose in interface EventQueue<T extends Event>