Re: Objects with Widgets, Save/Restore

[JD Smith <jdsmith(at)astro.cornell.edu>]

David Fanning wrote:
> 
> I wrote a minute ago:
> 
> > I played with it for days trying to keep the
> > current GUI (which, of course, has the RESTORE
> > button on it), but no matter what I tried (and
> > I thought I tried some pretty sophisticated
> > things) I couldn't get it to work. So now when
> > you hit the RESTORE button, the GUI disappears
> > and comes back a second later with the old
> > session up and ready to go.
> 
> After reading JD's post, I'm pretty sure
> there is a way to get this to work. In fact,
> I believed that for the 3-4 frustrating days
> I spent working on the problem. I *still*
> believe it. I just can't get it to work. :-(
> 

The secret is this same notion of pruning out the bits you don't need. 
Here's a sketch of how I'd approach your problem.

pro DavidsPlayhouse::Restore
  oldself=self               ;for killing later
  wInfo=self.wInfo           ;save the GUI, eat soy products
  self.wInfo=ptr_new()	     ;detach, avoiding the carnage
  restore_obj, self.SaveFile ;travel back in time
  obj_destroy,oldself        ;kill our old self, except wInfo
  self.wInfo=wInfo           ;reattach our saved widget info
  self->UpdateGUI            ;I'm not who I think I am
end

where "restore_obj" restores an object on top of itself.  At least I
think this is what you're trying to do.  I once called this
"transmogrification" ... to the delight and ridicule of various
newsgroup regulars.  It relies on the fact that the variable "self" is
actually passed by reference to all methods, so you can overwrite it
simply by restoring from file an object previously saved under a
variable name "self" (try "self=1" in a method sometime and see what
trouble you'll get yourself into).  Hopefully, this is an object of the
same type, or you'll be in for some surprises.  Notice how I killed my
old self (after carefully detaching the GUI components I wanted to
escape the Cleanup carnage), to avoid having a split personality (and
memory leaks).

The secret to keeping the same GUI running across this restore process
is simple: isolate all widget state info under a pointer, detach it
beforehand, and retain it across the restore, for grafting onto the
newly reanimated object.  As long as all widget ID's and state
information survive the (wait for it) transmogrification, you won't have
any GUI flashing, since it'll be the same damn widgets running all
throughout (yes, including the button which invoked the command).  I'd
also isolate the restore code in some error checking.  I can send you an
entire example if you're interested.  And by the way, to avoid the
confusion Pavel identified, I call this feature "Revert from Disk...",
as in "Go back to that version I saved before I did that stupid thing". 
It's very handy.  Do also consult the restore_obj writeup on your own
website for some of the potential snafu's associated with object
restoration.

Good luck,

JD