| Re: event_pro for compound widgets [message #40931] |
Tue, 07 September 2004 20:41 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Benjamin Hornberger writes:
> I am quite confused now and can't figure out how to write a compound
> widget which has an event_pro keyword and behaves like a regular basic
> widget. Sorry for the lengthy message...
>
> My compound widget is supposed to control a stepping motor and will
> consist of a non-editable field with the current position, editable text
> fields for "move to position" and "move by distance", a slider to set a
> step size and two buttons to move forward and backward in steps whose
> step size is set by the slider. As text fields, I am using David
> Fanning's fsc_field.
>
> This compound widget I want to include in other widgets by something like
>
> motor1_id = cw_move_motor(parent, ..., event_pro = 'motor1_event')
>
> When I change the step size of the slider, this should only affect the
> CW itself (updating its internal "stepsize" value and a displayed
> number"). I could manage to do that already.
>
> All other events (hitting enter in the moveto or moveby field, or
> clicking the forward / backward buttons) should send an event structure
> to motor1_event.pro (something like { CW_MOVE_MOTOR, id: id, top: top,
> handler: handler, type: 0L, moveby: 0D, moveto: 0D, stepsize: 0D } where
> type holds a code for whether it was a moveto or moveby request, etc.).
>
> Then, of course I would want to write
>
> PRO motor1_event, event
> ...
> IF event.type EQ 0 ...
>
>
> Now, what do I do? In the CW definition function, I define
> event_func='cw_move_motor_event' for my fsc_fields, buttons etc., This
> cw_move_motor_event.pro will create and return the desired event
> structure. But where is that returned to?
>
> And of course I have to define a keyword event_pro in my CW definition
> function which will hold a string with the event handler procedure's
> name. How do I make sure that in case of an event, my event structure is
> created and passed to that procedure?
You are on the right track here, in fact you have done almost
everything right. Almost. :-)
The way event handling works is that an event that gets into
an event handler *procedure* is acted upon and the event is
then said to be "swallowed". It doesn't go any further.
But if the event handler is a *function*, there are other
possibilities. Functions return values. If the return value
from an event handler function is a structure, and if that
structure has ID, TOP, and HANDLER fields, then the return
value is treated as if it were an event structure, and the
event "bubbles up" from that event handler in the normal
way all events "bubble up" a widget hierarchy.
So, if your compound widget event handler is a function (use
the EVENT_FUNC keyword instead of the EVENT_PRO keyword to
assign it), then you have the possibility of having an event
"bubble up" to the next higher widget in the widget hierarchy,
I.e., the parent of the compound widget. If you don't want the
event to bubble up (that is, you wish to swallow the event),
then just return something from your event handler function
that is not a structure. (A zero is typically used.)
*But* you want to be able to *assign* an event handler to
the compound widget (and who wouldn't?). So you are
probably going to have to create EVENT_PRO (and, to be
complete) EVENT_FUNC keywords for your compound widget,
and store the results in your info structure.
So then, you get to the end of the compound widget event
handler, and you have some choices to make:
myEvent = {ID:info.tlb, TOP:event.top, HANDLER:0L, ...}
; Do I want to return anything? No!?
IF handled THEN RETURN, 0
; Did the user provide an EVENT_PRO?
IF info.event_pro NE "" THEN BEGIN
Call_Procedure, info.event_pro, myEvent
RETURN, 0
ENDIF
; Did the user provide an EVENT_FUNC?
IF info.event_func NE "" THEN BEGIN
ok = Call_Function(info.event_pro, myEvent)
RETURN, 0
ENDIF
; Do I want to pass the event along to my parent? Yes!
RETURN, myEvent
That should get you going. :-)
Cheers,
David
--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http:/www.dfanning.com/
Phone: 970-221-0438, IDL Book Orders: 1-888-461-0155
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