Gorm FAQ

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Why does Gorm give me a warning when I have bundles specified in GSAppKitUserBundles?
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Gorm maintainer and others are currently, as of this writing, working on implementation Gorm maintainer and others are currently, as of this writing, working on implementation
of modern XML nib support in GNUstep. of modern XML nib support in GNUstep.

Revision as of 15:44, 8 September 2006


Should I modify the data.classes of file in the .gorm package?

   My advice is never to do this, ever.  Some have said that "they're plain text 
   and I should be able to change them".   My response to this rather weak rationale 
   is that if they are modified I cannot and will not guarantee that Gorm will be able 
   to read them or will function correctly if it does.

Why does my application crash when I add additional attributes for encoding in encodeWithCoder: or initWithCoder: in my custom class?

   If you've selected the custom class by clicking on an existing object and then 
   selecting a subclass in the Custom Class Inspector in Gorm's inspector panel, 
   then when the .gorm file is saved, Gorm must use what is called a template to 
   take the place of the class so that when the .gorm is unarchived in the running 
   application, the template can become the custom subclass you specified.  Gorm has 
   no way of knowing about the additional attributes of your subclass, so when 
   it's archived the template depends on the encodeWithCoder: of the existing 
   class.  Also, when AppKit loads the .gorm file, the initWithCoder: on the 
   subclass is called to allow the user to do any actions, except for additional 
   encoding, which need to be done at that time.  This is particularly true 
   when non-keyed coding is used, since, with keyed coding, it's possible to 
   skip keys that are not present.  The application may not crash if keyed coding 
   is used, but Gorm would still not know about the additional attributes and 
   would not be able to persist them anyway.
   Please see information in previous chapters regarding palettes, if you 
   would like to be able to add your classes to Gorm so that they don't 
   need to be replaced by templates, or proxy objects.

Why should I be careful when using Gorm with GSAppKitUserBundles?

   Some bundles may use poseAs: to affect change in the existing behavior
   of some GNUstep classes.  The poseAs: method causes an issue which may
   cause Gorm to incorrectly encode the class name for the object which 
   was replaced.   This makes the resulting .gorm file unusable when 
   another user who is not using the same bundle attempts to load it.

How can I avoid loading GSAppKitUserBundles in Gorm?

You need to write to Gorm's defaults like this:

       defaults write Gorm GSAppKitUserBundles '()' 

Doing this overrides the settings in NSGlobalDomain for Gorm and forces Gorm not to load any user bundles at all. To eliminate this simply do:

       defaults delete Gorm GSAppKitUserBundles 

How can I change the font for a widget?

   This is a simple two step process.  Select the window the widget is
   in and then select the widget itself, then bring up the font panel 
   by hitting Command-t (or by choosing the menu item).  By doing this 
   you're making the window the main window and by selecting the widget, 
   you're telling the editor for that object to accept changes.   Then 
   you can select the font in the panel and hit "Set".  Remember to set 
   the pop up button to "As Selected Above".   For some objects, the 
   font panel isn't effective because those objects can't have a font directly 

Does Gorm use "fake" objects in the Gorm gui when building the model?

   No, it doesn't.  While it's true that Gorm proxies some of the custom 
   objects for the user in various ways described above in #2, Gorm uses 
   actual instances of most objects to do it's work.   Gorm utilizes special
   classes called Editors.  These editors wrap the actual instance and make 
   it possible for Gorm to modify aspects of those objects.   For instance,
   a button in a Gorm model is selected (i.e. knobs appear around it) when 
   the user selects it.   The knobs and the ability to change things about the
   selected button are enabled by the button editor.   Normally, the button
   would simply have been pressed.

Does Gorm itself encode/decode the objects in the .gorm file?

   Yes and no.  Gorm relies heavily on the use of NSArchiver and NSUnarchiver.
   These two classes are absolutely vital to Gorm's operation.  They facilitate
   the use of proxy objects described above which is essential to Gorm's function.
   All of the code for actually saving the objects in the model resides in AppKit.
   The method initWithCoder: and encodeWithCoder: (the NSCoding protocol) are
   implemented on every object in both gui and base which are capable of being
   encoded.   Gorm utilizes these methods and the above mentioned techniques to
   do it's job.

Who should release the top level objects?

   After the .gorm file is finished loading, all of the top level objects should
   have a retain count of one.  It is the responsibility of the File's Owner/NSOwner
   to release these objects.  The NSOwner, as previously described, is usually the 
   controller class which loaded the file.  In the case of NSWindowController, the
   window controller should release all of the top level objects for you.

Why doesn't Gorm/GNUstep read nib files?

   Until recently, the format of the NeXT nibs has been simply a serialized binary.
   Now that Apple's nibs are XML based using the NSKeyedArchiver and NSKeyedUnarchiver, 
   it makes it easier to reverse engineer the format and allow GNUstep and Gorm to read
   the nib files.
   The older, non-xml, serialized format really isn't a "format" as much as it is a 
   byte stream.   Part of the issue is that the data encoded in the nibs is
   strongly tied to the implementation of each control.   Additionally, each control has
   serveral versions and it's possible for different versions to be combined.   So, in
   order to reverse engineer this we would need to understand the internal implementation
   of each and every control and know in what sequence each of it's attributes is stored
   as well as implement every version of each control and make whatever corrections need
   to be made when loading an older version into a newer implementation, etc ,etc.   Add
   to this that Apple/NeXT would likely change the encoding of some classes between each
   version and may even change the internal implementation, which would require a full
   investigation into all of the classes to ensure that our encoding matches for every
   version of every class.
   With the keyed nibs, this is no longer an issue.   Forward and backward compatibility
   is possible with them and it eases the burden each time there is a new release.   The
   Gorm maintainer and others are currently, as of this writing, working on implementation
   of modern XML nib support in GNUstep.