On Sun, Aug 31, 2008 at 11:45 AM, Meik Schuetz <[EMAIL PROTECTED]> wrote: > Dear everyone, > I am trying to create my own NSCoder implementation to serialize objects to > a XML format which would like to use to communicate with WCF service. The > serialization is already done and I had no problems do it, however I've got > some conceptional questions about the de-serialization: > > Given the serialized XML: > <EntityKey> > <stringValue>HELLO WORLD</stringValue> > <boolValue>True</boolValue> > <intValue>12</intValue> > <compositeValue> > <stringValue>THIS IS THE SECOND INSTANCE</stringValue> > <boolValue>False</boolValue> > <intValue>4711</intValue> > <compositeValue></compositeValue> > <arrayOfString><Value>1</Value> > <Value>2</Value> > <Value>3</Value> > </arrayOfString> > </compositeValue> > <arrayOfString><Value>1</Value> > <Value>2</Value> > <Value>3</Value> > </arrayOfString> > </EntityKey> > > How would you de-serialize the node <CompositeValue> (which is a composite > value of type CompositeType, having the attributes stringValue, boolValue, > intValue, compositeValue and arrayOfString)? > > 1) Would you store information about the type in the XML and let the > NSCoding subclass have the intelligence to create and initialize the object > (ex. via NSClassFromString)? > 2) Or would you place this intelligence in the entity object's > :initWithCoder? If so, how would you create and initialize the composite > object passing the Coder reference?
You have to store type information in the XML. There's no other place for you to get it. You can't make that decision in -initWithCoder:, because -initWithCoder: supposes that you have *already* discovered the type and allocated an instance of the class in question. It's like trying to find your friend's phone number by calling him to ask him what it is. That said, I'm not sure that NSCoder is a good API for you to use for this in any case. Your XML looks like it's a typical XML document, with a tree structure of fairly regular values. NSCoder is an API for encoding arbitrary object graphs, which can include disconnected sets, multiple references to a single object, and even cycles. It can encode arbitrary objects, arbitrary data for those objects, and arbitrary relationships between them. NSKeyedArchiver can already produce XML. If you look at it, you'll find that it's very confusing. This is because of all the features it supports. Since XML is a tree structure, it has to do some fancy things to support arbitrary relationships. So if not NSCoder, then what? I'd suggest a simpler custom API, such as a general understanding that your classes will implement a -xmlRepresentation and -initWithXMLRepresentation: method pair, possibly creating and using NSXMLNode instances. This would allow you to create and decode XML without needing to go through an NSCoder. If you still do want to create an NSCoder subclass, then you might find mine helpful as some sort of guide. It's called MAKeyedArchiver and you can download it here: http://www.mikeash.com/?page=software/source.html It's intended to be a general-purpose archiver which writes to a custom binary file format, but you may (or may not) find its general design and approaches to be useful. If you do take a look at it, you should beware that I wrote it at a time when I was sure that the PowerPC 32-bit architecture was immortal, so the code makes a lot of bad assumptions about the size and endianness of basic data types. It should work fine on i386, but the archives won't be cross-architecture compatible. It will probably crash on PPC64 or x86-64. The need for MAKeyedArchiver has pretty much gone away, since Cocoa's built-in archivers have gotten a lot faster than they were when I wrote it. But just in case anyone happens to have a burning desire to fix the deficiencies I mentioned above, patches are welcome. _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to [EMAIL PROTECTED]
