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From: DAVISM@kcgl1.eng.ohio-state.edu (Michael T. Davis)
Newsgroups: comp.windows.x
Subject: Re: Problem with Dwt List Box (callback data)
Message-ID: <3045@quanta.eng.ohio-state.edu>
Date: 15 Sep 89 20:02:07 GMT
References: <3035@quanta.eng.ohio-state.edu>
Sender: news@quanta.eng.ohio-state.edu
Organization: Ohio State University
Lines: 66


	In article <3035@quanta.eng.ohio-state.edu>, I wrote:

>
>	I am experiencing a problrm with the callback data structure passed
>to my callback function for a DECwindows Toolkit (Dwt) List Box widget.  I
>am running DECwindows under VMS 5.1-B on a VAXstation 3100.  Here's the
>List Box set up code:
>
>[list box setup deleted]
>
>And here's the callback:
>
>void list_callback ( widget, user_data, callback_data )
>    Widget * widget;
>    caddr_t user_data;
>    DwtListBoxCallbackStruct callback_data;
>[body of callback deleted]
>
>The reason member and item_length of the callback data structure always have
>bogus values in them and the item_number member is always 0.  All the structure
>members stay constant, no matter which item I select with the pointer.  Is
>there something really obvious I am forgetting, or what?

	As it turns out, the copy of the DECwindows docs we have lays out the
parameters to the callback exactly as I have them above.  In fact, the widget
should be passed by value and the callback_data should be passed by reference.
All is well with the List Box now.

	But here's another problem... Within the same application, I want to
create a Push Button which the user can "press" and activate a callback.
Here's the setup code:

    push_button = DwtPushButton ( main_window, "Cancel Button", 30, 175,
     DwtLatin1String ( "Cancel" ), NULL, NULL );
    XtAddCallback ( push_button, DwtNactivateCallback, cancel_callback, NULL );
    XtSetArg ( settings [ 0 ], DwtNconformToText, True );
    XtSetValues ( push_button, settings, 1 );
    XtManageChild ( push_button );

And here's the callback:

static void cancel_callback ( widget, user_data, callback_data )
    Widget widget;
    caddr_t user_data, callback_data;
{
    parse_verb ( & 0 ); /* parse_verb is FORTRAN code, so need to pass
                           integer value by reference */
}

The main_window (parent) is a Dialog Box.  I have two other children in the
Dialog Box, the aforementioned List Box and a Label.  The problem is that the
push button never appears.  I don't get any errors, but I don't see a Push
Button either.  Any ideas?

							Thanks,
							 Mike

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