[wx-dev] PG DN and PG UP of wxVListBox

[Azriel Fasten]

Currently the code for handling PG DN and PG UP in OnKeyDown of wxVListBox
is:

        case WXK_PAGEDOWN:
            PageDown();
            current =3D GetVisibleBegin();
            break;

        case WXK_PAGEUP:
            if ( m_current =3D=3D (int)GetVisibleBegin() )
            {
                PageUp();
            }

            current =3D GetVisibleBegin();
            break;

Ok, so there are two problems,

   1. case WXK_PAGEDOWN: if the page is not scrolled ( suppose it all
   fits ), PageDown() has no effect, and current goes to the top, resulting=
 in
   PG *DN* going *up*. Obviously wxListBox's behaviour is different as
   well.
   2. case WXK_PAGEUP: a more subtle problem, it doesnt match wxListBox
   behaviour, as the first PG UP will not PageUp at all, rather just select=
 the
   current first visible item, unless the current item is the current first
   visible item.

wxListBox's behaviour is the same for both up and down ( note that I only
tested wxListBox on wxMSW ). For PG DN*, *it makes the currently selected
item the top item ( ScrollToLine ) and then selects the last visible item.
For PG UP, it makes the currently selected item the bottom item, and then
selects the first visible item. For PG UP, a design choice has to be made
about which behaviour suites it most, the current behaviour, or to emulate
wxListBox behavior.

Preliminary code to solve #1:
        case WXK_PAGEDOWN:

            //go down a page
            ScrollToRow( m_current );
            //select the last ( fully ) visible item. GetVisibleEnd()
returns last item +1 ( therefore subtract 1 ),
            //fixme: however sometimes that item is only partialy visible
and normal behaviour would be to subtract another
            current =3D GetVisibleEnd() - 1;
            break;

I wasn't able to effectively emulate PG UP correctly.
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