Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!samsung!usc!apple!lai
From: lai@Apple.COM (Ed Lai)
Newsgroups: comp.sys.mac.programmer
Subject: Re: 3 (very basic) AppleEvent programming questions
Message-ID: <48925@apple.Apple.COM>
Date: 7 Feb 91 17:33:05 GMT
References: <1991Feb6.185413.1@gsbacd.uchicago.edu>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 64

In article <1991Feb6.185413.1@gsbacd.uchicago.edu> gft_robert@gsbacd.uchicago.edu (opcode ranger) writes:
>-- 
>I have 3 basic System 7 questions:
>
>1) How do you tell if you've actually been passed a default reply to your AE
>handler?  (The docs seem to say that it's an optional thing that the client can
>request or not). Check reply.dataHandle to see if it's not nil?
>

Yes, check to see if reply.dataHandle = nil.

>2) If you want to handle all core AE's in order to "System 7 friendly", but
>your app doesn't print, should you just return noErr from your 'Print Docs' AE
>handler?
>

The easiest way is not to provide a 'pdoc' handler at all. If the client had
asked for a reply, he would automatically get a eventNotHandled error as a
'errn' parameter in the reply.

>3) I'm a bit confused about how all AEDesc's are substitutable for one another.
>If the typedef for the basic AEDesc is of this form:
>
>	DescType descriptorType;
>	Handle dataHandle;
>	
>and an AppleEvent == AERecord == AEDescList == AEDesc, does this mean that an
>AppleEvent -- in addition to containing the keyword descriptors for attributes
>and parameters -- also has a descriptorType and dataHandle itself? (obviously I
>have no idea what I'm talking about, so feel free to straighten me out :->;
>I've read the relevant section of IM VI numerous times, but I  guess I'm just
>missing the new paradigm and trying to make the AE's not abstract enough).
>

Think of it in an object oriented way. AEDesc is the basic object. 
AEDescList is a list of AEDesc, it is a subclass of AEDesc.
AERecord is an AEDescList where each element has a keyword, it is a subclass
of AEDescList.
AppleEvent is a special kind of AERecord used for communication between
processes, it is a subclass of AERecord.
So AEDisposeDesc has an AEDesc as the parameter, but you can use it also for
AEDescList/AERecord/AppleEvent.
So AECountItems count the number of items in an AEDescList, but you can
also use it to count the number of parameters in AERecord/AppleEvent.


>Any help much appreciated!
>
>
>Robert
>
>============================================================================
>= gft_robert@gsbacd.uchicago.edu * generic disclaimer: * "It's more fun to =
>=            		         * all my opinions are *  compute"         =
>=                                * mine                *  -Kraftwerk       =
>============================================================================

/* Disclaimer: All statments and opinions expressed are my own */
/* Edmund K. Lai                                               */
/* Apple Computer, MS37-UP                                     */
/* 20525 Mariani Ave,                                          */
/* Cupertino, CA 95014                                         */
/* (408)974-6272                                               */
zW@h9cOi