axaptapedia: Event broker

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Источник: http://www.axaptapedia.com/Event_broker
==============

Summary: /* Global broker */

==Purpose==
* To allow [http://en.wikipedia.org/wiki/Event-driven_programming event driven programming]
* To have [http://en.wikipedia.org/wiki/Loose_coupling loose coupling] between classes
* A (partial) implementation of the [http://en.wikipedia.org/wiki/Observer_pattern Observer pattern]

==Download==
[http://www.axaptapedia.com/images/2/...ventBroker.xpo SysEventBroker.xpo (11 KB)]

==Implementaion==
Three classes are provided:

# ''SysEventListener'' is the interface class for a "listener"
#* ''gotEvent'': every listener must implement
# ''SysEventInfo'' is an implementation for a listener, which simply put received information on the [[Infolog]]
#* ''main'': contains a simple test case
# ''SysEventBroker'', which client classes use to register and notify listeners, it implements the following methods:
#* ''addListener'': to register a listener
#* ''removeListener'': to unregister a listener
#* ''fireEvent'': to fire an event and to notify listeners via the ''gotEvent'' method

==Global broker==
Client classes need to share a SysEventBroker instance.
A possible solution is to use the global [[Infolog]] object.

In the ''Info.classDeclation'' add:

SysEventBroker eventBroker;


Add a new method:

public SysEventBroker eventBroker()
{
if (!eventBroker)
eventBroker = SysEventBroker::construct();
return eventBroker;
}


Beware, ''Infolog'' lives at the client, all notified infomation is sent to the client.

You could make the same implementation in the ''Application'' class which lives at the server.
But you must then remember to use the same broker.

==Example use==


static void SysEventTest(Args _args)
{
SysEventBroker broker = SysEventBroker::construct();
SysEventInfo info1 = new SysEventInfo("Info-1"); // catch all;
SysEventInfo info2 = new SysEventInfo("Info-2"); // catch specific class
SysEventInfo info3 = new SysEventInfo("Info-3"); // catch specific type
;
// Setup
broker.addListener(info1, classNum(Object));
broker.addListener(info2, classNum(Runbase));
broker.addListener(info3, classNum(Object), "Fire 2"); // catch Fire 2
broker.addListener(info3, classNum(Object), "Fire 4"); // and Fire 4

broker.fireEvent(classNum(CustAutoCreate), "Fire 1", "This is my life");
broker.removeListener(info2, classNum(Runbase));
broker.fireEvent(classNum(CustAutoCreate), "Fire 2", "this is my time");
broker.fireEvent(classNum(CustAutoCreate), "Fire 3", "just show me the light");
broker.removeListener(info1);
broker.fireEvent(classNum(CustAutoCreate), "Fire 4", "and I go there");
}

Generated info:

Info-2 CustAutoCreate(Fire 1): This is my life
Info-1 CustAutoCreate(Fire 1): This is my life
Info-3 CustAutoCreate(Fire 2): this is my time
Info-1 CustAutoCreate(Fire 2): this is my time
Info-1 CustAutoCreate(Fire 3): just show me the light
Info-3 CustAutoCreate(Fire 4): and I go there


==Warning==
This is no silver bullet, do not abuse!
* Do not not use when standard method calls and argument passing is the easy solution.
* Do not forget to unregister the listener, even if an exception is thrown. Use try/catch!
* Registered listeners live as long as the broker, if it is ''Infolog.eventBroker()'' for the entire user session!

[[Category:Development tools]]


Источник: http://www.axaptapedia.com/Event_broker