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public interface EventQueue
An event queue.
An event queue is a many-to-many 'channel' to publish events and to subscribe
event listeners (EventListener
).
There are two kinds of event listeners: synchronous and asynchronous.
A synchronous listener works the same as a normal event listener
(listeners registered to a component (Component.addEventListener(java.lang.String, org.zkoss.zk.ui.event.EventListener)
).
It is executed one-by-one (no two even listener will be executed at the same time)
and under an execution (i.e., Executions.getCurrent()
never null).
In additions, it is allowed to manipulate the components belonging
to the current execution.
On the other hand, an asynchronous listener is executed asynchronously
(in a working thread).
It can not access the components belonging to any desktop.
There is no current execution (Executions.getCurrent()
is null}.
However, it is useful to make the application more responsive when
executing a long operation. A typical use is to execute the long operation
in an asynchronous listener, and then all other events can be processed
concurrently.
Method Summary | |
---|---|
void |
close()
Closes the event queue. |
boolean |
isSubscribed(EventListener listener)
Returns if an event listener is subscribed. |
void |
publish(Event event)
Publishes an event the queue. |
void |
subscribe(EventListener listener)
Subscribes a listener to this queue. |
void |
subscribe(EventListener listener,
boolean async)
Subscribes a synchronous or asynchronous listener to this event queue. |
void |
subscribe(EventListener listener,
EventListener callback)
Subscribes a synchronous or asynchronous listener to this event queue. |
boolean |
unsubscribe(EventListener listener)
Unsubscribes a listener from the queue. |
Method Detail |
---|
void publish(Event event)
If this is a desktop-level event queue, this method must be called
within an activated exection,
i.e., Executions.getCurrent()
not null.
On the other hand, if this is an application-level event queue, it is OK to be called without the current execution.
java.lang.IllegalStateException
- if this method is called
not within an activated execution (such as a working thread),
and this is a desktop-level event queue.void subscribe(EventListener listener)
subscribe(listener, false)
(subscribe(EventListener,boolean)
. In other words,
it subscribes a synchronous listener.
Note: this method must be called within an activated exection,
i.e., Executions.getCurrent()
not null.
Note: if this is an application-level event queue, the listener
shall not access the component associated with the event
Event.getTarget()
.
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.
subscribe(EventListener,EventListener)
,
subscribe(EventListener,boolean)
void subscribe(EventListener listener, EventListener callback)
Here is an example,
<window title="long operation" border="true">
<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 = "done"; //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
publish(org.zkoss.zk.ui.event.Event)
to publish the events. Refer to
another example in subscribe(EventListener,boolean)
.
listener
- the asynchronous listener to invoke when an event
is receivedcallback
- 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. Notice that the event argument is null
when the callback listener is called.subscribe(EventListener)
,
subscribe(EventListener,boolean)
void subscribe(EventListener listener, boolean async)
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 subscribe(EventListener,EventListener)
for example.
<window title="long operation" border="true">
<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 = "done"; //store the result
eq.publish(new Event("endLongOp")); //notify it is done
}
}
}, true); //asynchronous
//subscribe a normal listener to show the resul 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 asynchornous event listener requires Server Push which is available in ZK PE or EE, or you have to configure your own implementation.
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 exection,
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.
listener
- the listenerasync
- whether the listener is asynchronoussubscribe(EventListener)
,
subscribe(EventListener, EventListener)
boolean unsubscribe(EventListener listener)
Note: this method must be called within an activated exection,
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.
boolean isSubscribed(EventListener listener)
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.
void close()
Don't call this method directly. It is called only internally.
Rather, use EventQueues.remove(java.lang.String)
instead.
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