[Tkinter-discuss] Listbox size

[Bob van der Poel]

Thanks Micheal! I am going to save the "number of lines" snippet for future
reference.

Best,


On Wed, Feb 14, 2018 at 3:42 PM, Michael Lange <klappnase at web.de> wrote:

> Hi,
>
> On Tue, 13 Feb 2018 17:11:47 -0700
> Bob van der Poel <bob at mellowood.ca> wrote:
>
> > Getting closer :)
> >
> > I asked the question wrongly. I need to determine the number of VISIBLE
> > lines in the listbox.
>
> Should be (as used in my previous example)
>
>     visible_lines = lb.nearest(lb.winfo_height()) - lb.nearest(0)
>
> >
> > Using the .winfo_height() does return the height in pixels. Note: You do
> > have to make the widget visible before doing this, otherwise you just
> > get "1" returned. widget.update() works for this.
>
> I don't think the widget must actually be "visible"; it is only when the
> widget is initially created that the widget's dimensions are reported as
> 1*1 px. Calling update_idletasks() once after the widgets have been
> created should be sufficient to work around this.
>
> >
> > So, the next question is: what is the line size?
>
> That is definitely not needed for what you want to accomplish.
>
> >
> > Now, to make life much simpler :) I just played a bit and discovered
> > that if I make the listbox visible BEFORE the selection, it
> > automatically centers. So, my code now becomes:
> >
> >    self.lb.update()
> >    self.lb.select_clear(ACTIVE)   # needed to un-hilite existing
> > selection self.lb.see(x)
> >    self.lb.activate(x)
> >    self.lb.select_set(x)
> >
> > Easy. And I don't need to worry about the size of the box!
>
> Here see() does not necessarily center the given index. It sometimes
> appears near the top or the bottom of the list.
> And that's just what the manpage promises:
>
> " if the element is near one edge of the window then the listbox scrolls
> to bring the element into view at the edge; otherwise the listbox scrolls
> to center the element. "
>
> >
> > Well, mostly. If the selection I want is already on the screen, then the
> > box doesn't scroll to center. I think I can live with that.
>
> Good, again that's exactly what the listbox's manpage promises :)
> If you want exactly predictable behavior, I think you will have to use
> yview() instead.
>
> Best regards
>
> Michael
>
>
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