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From: byennaco@suneast.East.Sun.COM (Robert Yennaco - Sun BOS Software)
Newsgroups: comp.windows.news
Subject: Re:  scrolling lists in XView - a file dialog
Message-ID: <9006271544.AA01919@divet.East.Sun.COM>
Date: 28 Jun 90 00:32:52 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 80

I ran across a similar problem in SunView, so I'll describe it in those
terms and leave it to you to convert it to XView.

>	1) using xv_set, it is possible to either set a fixed number of
>	   strings for the list, or set an indexed string for the list.
>	   What I need is a variable number of strings. Something like
>	   **argv would have done the trick.

>	   To get a variable number of strings, it is necessary to insert
>	   one entry for each string. This is painfully slow and causes
>	   unnecessary flashing on the screen. Moreover, it is not possible
>	   to start with an empty list of entries --- there must be at least
>	   one or PANEL_LIST_INSERT dumps core.

>		xv_set(thing, PANEL_LIST_STRINGS, "", (char *) NULL, 0);
>		xv_set(thing, PANEL_LIST_INSERT, i
>			      PANEL_LIST_STRING, i, newvalue,
>			      0);

You can set up an attribute list, and make one call to panel_set().
The disadvantage here is that (at least in SunView) you're limited to
ATTR_STANDARD_SIZE=256 attributes in the list.  Needing 3 per value,
means you can bundle only 80 or so values into one panel_set() call,
keeping in mind that you still need the list NULL-terminator.  To get
rid of screen flickering, keep the item's PANEL_SHOW_ITEM attribute to
FALSE until you've completed list construction, then set the attribute
to TRUE.

This scheme might not suffice (performance-wise) if you're dealing with
a very large list, but it's better than doing each entry one at a time,
and the list can be as long as you want.

	char	*attr[ATTR_STANDARD_SIZE];
	int	num_attr = 0;
	for (i=0; i<n_values; i++)
		attrs[i] = (char *)PANEL_CHOICE_STRING;
		attrs[i+1] = (char *)(i-1)
		attrs[i+2] = newvalue;
		if ((num_attr+6) >= ATTR_STANDARD_SIZE) {
			attrs[num_attr+3] = NULL;
			panel_set(thing, ATTR_LIST, attrs, 0);
			num_attr = 0;
		}
		else
			num_attr += 3;
	}

	/*
         * If any attribute settings still on attribute buffer,
         * then send them now.
         */
        if (num_attr) {
                attrs[num_attr] = NULL;
                panel_set(thing, ATTR_LIST, attrs, 0);
        }


As you state, a better way is to use a string vector argument (**argv)
for PANEL_CHOICE_STRINGS.   I tried this long ago, and I recall getting
it to work (it was lightning-fast!), but now I can't for the life of me
figure out how I did it.  The disadvantage here (at least in SunView)
is that your list cannot exceed ATTR_STANDARD_SIZE=256 string values.


>	2) to change the entries, it is not possible to change all of them
>	   at once. I would have hoped something like:
>
>		xv_set(thing, PANEL_LIST_STRINGS, (char *) NULL, 0);
>
>	   would have done the trick. Instead it is necessary to delete
>	   them one at a time:
>
>		xv_set(thing, PANEL_DELETE_STRING, i, 0);
>
>	   Again, painfully slow and causes unnecessary screen updates.

Try the same scheme as described above.

Good luck!
-Bob