[Laszlo-dev] OpenLaszlo Event Model

[Max Carlson]

While we're on the subject, it would be nice if there was a way to store 
  data when registering the event that's returned when the event fires. 
  This is a common pattern for DHTML developers - methods registered for 
events often closes over instance-specific values that are then 
available to the callback...

Lorien (cc'd) made a proposal a while back along these lines...

P T Withington wrote:
> We have an (improvement 
> suggestion)[http://jira.openlaszlo.org/jira/browse/LPP-6034] to change 
> the structure of the event system to be more efficient and more 
> DOM-like.  I recently added a comment:
> 
>> What we really want to do is get more in line with 
>> http://www.w3.org/TR/DOM-Level-2-Events/
>>
>> This would mean that LzEventable would become EventTarget, and 
>> LzDelegatable [LPP-7037] would become EventListener.
>>
>> The major impact on our system is that LzEvents would no longer be 
>> objects in themselves, but simply names (event types). This could 
>> reduce the overhead of events, but would mean a big incompatibility. 
>> Instead of:
>>
>>   <target>.<event>.sendEvent(<value>);
>>
>> you would have to say:
>>
>>   <target>.dispatchEvent(<event>, <value>);
>>
>> [In DOM2, dispatchEvent takes only an Event as its argument, the event 
>> is an object that has attributes such as the event name (type), state, 
>> and depending on the type of the event, additional information -- what 
>> we usually pass as the single <value>. If we want to be more 
>> compatible, perhaps we should implement the `dispatchEvent` interface 
>> and another `dispatchSimpleEvent` interface that handles most of our 
>> events. Otherwise the overhead we save by not having LzEvent objects 
>> to attach listeners to will be replaced by allocating an Event object 
>> every time you want to send an event.]
> 
> I'd be interested in other ideas and opinions.

-- 
Regards,
Max Carlson
OpenLaszlo.org