| Re: Saving an application state [message #39935 is a reply to message #39841] |
Fri, 25 June 2004 04:39   |
robert.dimeo
Messages: 42
Registered: November 2001
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Member |
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Many thanks to all of you for your good ideas. This has been very helpful.
Rob
JD Smith <jdsmith@as.arizona.edu> wrote in message news:<pan.2004.06.25.01.36.40.142685@as.arizona.edu>...
> David is right, I do have a preferred method I've written about, and it's
> fairly easy. It essentially requires you to hide all the unnecessary
> widget info behind a single pointer. I usually use self.wInfo. Accessing
> said data is then a bit more tedious ((*self.wInfo).wButton instead of
> self.wButton), but it gives you two things:
>
> 1. Your object can live and run without a GUI. Good for batch scripts
> and command line processing.
>
> 2. You can save your object without the unnecessary (and harmful)
> transient widget data by simply "detaching" them before saving.
>
> A simplified version of my save method is:
>
> pro myClass::Save,file
> detwInfo=self.wInfo ; detach
> self.wInfo=ptr_new() ; a null pointer save, self,FILENAME=filename
> self.wInfo=detwInfo ; reattach
> end
>
> which works nicely, unless you have trouble saving (no permissions, etc.),
> in which case some error checking is a good idea:
>
> pro myClass::Save,file
> detwInfo=self.wInfo ; detach
> self.wInfo=ptr_new() ; a null pointer catch, serr
> if serr eq 0 then save,self,FILENAME=file catch,/CANCEL
> self.wInfo=detwInfo ; reattach if serr then message,'Error
> saving to file: '+file
> end
>
> Anyway, this is all you really need. Restoring is pretty simple, but you
> have to be a bit careful to make sure your restored object doesn't
> overwrite the class definition of a changed class (which in principle
> means compile that class before restoring). My RESTORE_OBJECT routine
> takes care of that (or you can do it yourself).
>
> Other fun tricks you can do with SAVE/RESTORE on objects include
> overwriting the existing "self" pointer in-place... a *very* easy way to
> implement "recover from file", which I call "transmogrification".
>
> David is right that SAVE very diligently follows the data structures
> thoroughly through all pointers and composited objects, and saves
> everything, but if you're careful to detach what you don't want or need,
> you'll be in fine shape. There's lots to read on the NG on this topic.
>
> JD
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