[plt-scheme] focus question

From: Jordan Johnson (jmj at fellowhuman.com)
Date: Sun Apr 19 19:40:18 EDT 2009

Hi all,

I have an editor-snip% subclass with two component editor-snip%s (top- 
snip and bottom-snip).  I've written a subclass of aligned-pasteboard 
% to align these two parts vertically, and so far, that works.  I'm  
now trying to get this behavior:

	1) Initially, the top-snip is hidden.
	2) When the pasteboard gets focus (which, to me, means the user  
clicks on it to enter text, same as DrS's comment boxes), the top- 
snip appears and gets focus.  (At this point, the user can also click  
the bottom-snip and type into it.)
	3) When the pasteboard loses focus, the top-snip is again hidden.

The questions:
	- Can I accomplish this with an on-focus handler in the pasteboard?
	- Is additional machinery needed, and if so, where?

Here is relevant code from an attempt at the aligned-pasteboard%  
     (inherit get-focus-snip set-caret-owner)
     (define/override (on-focus focus?)
       (if focus?
             (send the-top-part show #t)
             ;; the-top-part, above, is a vertical-alignment% I'm using
             ;; just for the ability to show/hide, as a wrapper  
around the snip.
             (unless (get-focus-snip)
               (set-caret-owner the-top-snip)))
           (send top-part show #f)))

I've tested this in the REPL and in an independent window, and it  
seems to successfully accomplish (1) and (2), but not (3).  My hunch  
is that it's because some of the events I want are being handled only  
by the component snips, but after reading the docs I'm still not  
clear on how to work around that (if indeed that's the case).

Thanks again,

Posted on the users mailing list.