Path: utzoo!attcan!uunet!husc6!bloom-beacon!ATHENA.MIT.EDU!swick
From: swick@ATHENA.MIT.EDU (Ralph R. Swick)
Newsgroups: comp.windows.x
Subject: Re: can callbacks map widgets in realized parents?
Message-ID: <8808031406.AA02529@LYRE.MIT.EDU>
Date: 3 Aug 88 14:06:50 GMT
References: <8808031313.AA00898@dinorah.wustl.edu>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: DEC/MIT Project Athena
Lines: 24

The answer to your subject question is yes, but the scenario you
describe is a lot more complicated.  Remember that geometry negotiation
behaves very differently before and after a widget (branch) is realized.

When a widget hierarchy is created and managed before any of its
ancestors have been realized, then geometries are effectively
calculated from the inside out.  This allows each parent's layout
routine to be called exactly once and have full information on 
the desires of it's children.  Once the hierarchy has been
realized, however, the parent must react to each individual change
in it's managed set of children and must negotiate any changes
in it's own geometry with it's parent.  Thus, geometries of realized
hierarchies are effectively calculated from the outside in.

One technique that will work well when you want to create and destroy
branches of a realized tree is to leave the uppermost node of the
branch unmanaged until the remainder of the branch has been created
(and managed).  You can then set the uppermost node to be managed,
which will also cause the entire branch to be realized.  You may
also want some way to inform the parent of the new branch not to
perform a re-layout operation between the time you destroy the
old branch and manage the new one.  Some composite widgets will
support this (deferring a re-layout) and some won't.  The better
one probably will.