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-descriptorAtIndex: limitations (Re: Extract text out of NSAppleEventDescriptor)

Christopher Nebel wrote:

Incidentally, getting a particular value out of an AERecord (or an
AppleEvent, such as you have) using -descriptorAtIndex: is not
reliable, since there may be other items, and they're not guaranteed
to be in any particular order.  Use "descriptorForKeyword:'----'"
instead.


This is a weakness of the NSAppleEventDescriptor API. The C equivalent, AEGetNthDesc, returns both key and value, whereas - descriptorAtIndex: returns only the value. This makes it impossible for NSAppleEventDescriptor to unpack AERecords containing arbitrary keys; instead you have to get a pointer to the raw AEDesc and iterate over it using AEGetNthDesc. See objc-appscript's [AEMCodecs - unpackAERecord:] method for an example of how to do this [1]:

	http://appscript.svn.sourceforge.net/viewvc/*checkout*/appscript/objc-appscript/trunk/src/Appscript/codecs.m

BTW, if anyone fancies filing a feature request, the proper solution would be for NSAppleEventDescriptor to provide a -keys or - keyAndDescriptorAtIndex: method. While you're at it, you might also ask for C and ObjC APIs to iterate over an AppleEvent's attributes, since neither currently provides a way to extract event attributes without knowing all the keys in advance.

has

[1] Or, heck, just use AEMCodecs to do all your packing and unpacking for you; that's what it's there for.
--
http://appscript.sourceforge.net
http://rb-appscript.rubyforge.org

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