| Re: Passing info and destroying widgets... [message #15892 is a reply to message #15879] |
Mon, 21 June 1999 00:00   |
Liam Gumley
Messages: 473
Registered: November 1994
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Senior Member |
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Dirk Fabian wrote:
> Here's something i can't figure out... I'm following the advice of DF and
> communicating between my widgets with info structures. All is well, but now i
> want to pass the info structure from the event handler back to the parent widget
> with
>
> WIDGET_CONTROL, event.top, SET_UVALUE=lines, /NO_COPY
>
> and then destroy the widget. But you can't do this, because WIDGET_CONTROL (i
> think) dereferences event.top so that
>
> WIDGET_CONTROL, event.top, /DESTROY
>
> fails since it doesn't know where to look. (you can't even put in a dummy to hold
> the event.top number, the widget itself is gone from that id)
>
> Unfortunately, you can't /DESTROY the top widget first and expect to set it's
> UVALUE later, either. So what do i do here? I tried putting a flag in my
> info structure to trigger the base widget destruction back in the widget
> definition level (not in the event handler), but i can't figure out when the
> program would be able to look at that newly inserted flag.
Dirk,
If I understand your question correctly, you are trying to figure out
how to pass a value from a widget event manager back to the calling
program (i.e. the one that invoked XMANAGER) after the top level widget
has been destroyed. The answer in IDL5 is pointers.
In a widget which does not need to return any information, you store the
info structure in the top level base user value, e.g.
;- Create widgets...
;- Create info structure
info = {name:'test', value:indgen(10)}
;- Store info structure in top level base
widget_control, tlb, set_uvalue=info
;- Start XMANAGER...
However when the event manager must pass back information to the program
which invoked XMANAGER, use a pointer to store the info structure, and
store the *pointer* in the top level base user value, e.g.
;- Create widgets...
;- Create info structure and store via pointer
info = {name:'test', value:indgen(10)}
ptr = ptr_new(/allocate_heap)
*ptr = info
;- Store pointer in top level base
widget_control, tlb, set_uvalue=ptr
;- Start XMANAGER...
and then in the event manager, get the contents of the info structure
from the pointer, e.g.
;- Get pointer
widget_control, event.top, get_uvalue=ptr
;- Get info structure
info = *ptr
When the top level base is destroyed, the *pointer* still exists, thus
in the calling program you can retrieve it's value.
Cheers,
Liam.
--
Liam E. Gumley
Space Science and Engineering Center, UW-Madison
http://cimss.ssec.wisc.edu/~gumley
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