Re: Keyed decoding of geometry

[Fred Kiefer]

Richard Frith-Macdonald wrote:
> On 24 Jan 2004, at 17:06, Fred Kiefer wrote:
> > And I also tried to write a few sample decoding methods based on that 
> > NIB file. I made specific methods out of them, so that it will be 
> > easier to keep them a bit apart from our current decoding code. 
> > Actually I would like to see some method like the follwoing on 
> > NSObject so we dont have to mix the different code in one method:
> >
> >
> > - (id) initWithCoder: (NSCoder*)aCoder
> > {
> >   if ([aCoder allowsKeyedCoding])
> >     {
> >     self = [self initWithKeyedCoder: aCoder];
> >     }
> >     else
> >     {
> >     // call old decoder code, for which I don't have a great name
> >     }
> > }
>
>
> Maybe, on the other hand, keeping the two together might be considered a 
> virtue ... certainly if the code involved is small.
We should try to get more opinions on this. The pros for a separate 
hierarxchy for each encoder type arethat the methods are shorter and 
cleaner and that calls to super may use the short cut, as they know what 
sort of archiver they are dealing with. For the cons I only see the 
additional method call.


> > And now to show you how easy some base classes could be decoded:
> >
> > @implementation NSArray (NSKeyedCoding)
> >
> > - (id) initWithKeyedCoder: (NSCoder*)aCoder
> > {
> >   NSArray *array = [aCoder decodeObjectForKey: @"NS.objects"];
> >
> >   [self initWithArray: array];
> >   return self;
> > }
> >
> > @end
> >
> > @implementation NSSet (NSKeyedCoding)
> >
> > - (id) initWithKeyedCoder: (NSCoder*)aCoder
> > {
> >   NSArray *array = [aCoder decodeObjectForKey: @"NS.objects"];
> >
> >   [self initWithArray: array];
> >   return self;
> > }
>
>
> I'm not sure this is right ... I think you are looking at something I've 
> not impemented yet (and not even fully investigated).
> It appears that the keyed archiver implements 
> -encodeArrayOfObjCType:length:at: by creating a temporary object of a
> private class in which to encapsulate the array, then encodes that 
> temporary object.  The temporary object encodes itsself
> by writing various items with names like 'NS.objects'
> To implement this properly, I need to figure out exactly how the private 
> class (_NSKeyedCoderOldStyleArray) encodes itsself for arrays of 
> different types of data.
>  Quite possibly there are other things missed ... I haven't played with 
> it to see how MacOS-X implements encodeValuesOfObjCTypes: for instance.

I did not say that my code is already usable. BUt as soon as your 
decoder is running it should work.