| Re: Event handler as an object method ?? [message #41660 is a reply to message #41601] |
Thu, 11 November 2004 06:26   |
Benjamin Hornberger
Messages: 258
Registered: March 2004
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Senior Member |
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David Fanning wrote:
> Antonio Santiago writes:
>
>
>> Hi,is there a reason why an object method can't be use as an event handler?
>
>
> No reason at all. In fact, it is only short step
> now before you realize widgets should be objects. :-)
>
>> I just created an object that "contains" a WIDGET_DRAW. I'd like that
>> the event ocurred on WIDGET_DRAW was handled by a method of my class,
>> but EVENT_FUNCTION and EVENT_PRO keywords not accpet a method.
>>
>> The solution i have adopted is to catch the event of WIDGET_DRAW outside
>> of the object (on a WIDGET_BASE where i put the object (realy de
>> WIDGET_DRAW)) and redirect it to the method i want
>> (MyObject->EventHandler), but this is an ugly solution.
>
>
> In the absence of help from RSI, most solutions are more
> or less ugly. The solution I usually adopt is to have
> all events go to a generic event handler. In the event
> handler, a "command" structure is extracted from the user
> value of the widget that caused the event. The "command"
> is an anonymous structure containing an "object" and
> a "method" field. All the event handler does is extract
> the command structure and use CALL_METHOD to call the
> method field on the object field, passing the event structure
> as a parameter to the "event handler method".
>
> To make this work, every widget that is going to generate
> an event has a "command" structure stored in its user value:
>
> drawID = Widget_Draw(tlb, XSize=400, YSize=400, $
> UValue={object:myobject, method:'MyEventHandlerMethod'})
>
> The generic widget event handler does this:
>
> Widget_Control, event.id, Get_UValue=cmd
> Call_Method, cmd.method, cmd.object, event
>
> In my Catalyst Library, all widgets are objects and the
> "fields" of the "event structure" all point to objects
> as well, so this slight of hand feels a little more
> natural. Instead of using Event_Pro or Event_Func
> to direct events, you can use an Event_Method keyword
> to define the appropriate method to handle the event
> If an event method is not specified, we use a EventHandler
> method that is always associated with an widget object.
>
> Cheers,
>
> David
>
Is it right that in this case (as David proposes), you don't need the
widget_control, event.top, get/set_uvalue=info, /no_copy
any more to pass the widget's (now object's) internal variables around?
Instead, you can just access the members of the self structures in the
"event handler"? That would be nice...
Benjamin
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