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From: wdh@well.sf.ca.us (Bill Hofmann)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Problem with GetResource in a cdev
Message-ID: <21923@well.sf.ca.us>
Date: 2 Dec 90 18:50:51 GMT
References: <48578@eerie.acsu.Buffalo.EDU>
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 39

In article <48578@eerie.acsu.Buffalo.EDU> volaski@acsu.buffalo.edu (Maurice Volaski) writes:
>oldResFile=CurResFile();	/*save reference number to cdev's*/
> 							/*resources*/
>*resNum=HOpenResFile(vRefNum,dirID,fileName,fsRdWrPerm); /*open my file's 
>					/*resource fork*/
>tempRes=GetResource('EXL ',-4048);	/* GetResource succeeds here*/
>UseResFile(oldResFile);		/* make cdev resource file current*/
>tempRes=GetResource('EXL ',-4048);	/* PROBLEM: GetResource fails*/
>num=CountResources('EXL ');		/* CountResources succeeds*/
>tempRes=GetIndResource('EXL ',1);	/*GetIndResouces succeeds*/
>
>Even though the file's resources are not current, GetResource should iterate 
>through the list of open resource files and find the resource. Interestingly, 
>CountResources and GetIndResource both succeed. Also, GetResource does 
>succeed when the file's resources are current.
>
>Anyone have a clue as to why GetResource fails in this particular instance?
I'm suprised that CountResources and GetIndResource works.  Here's the 
scenario:  At the beginning of your code, the resource chain (the path the
Resource Manager uses to search for resouces) is like so:

	<START HERE>->cdev->DA Handler->System

After the HOpenResFile, it's like so:

	<START HERE>->fileName->cdev->DA Handler->System

so naturally, if an 'EXL ' -4048 resource is in fileName, it succeeds.
**THEN** you call UseResFile, it looks like *this*:

		<START HERE>
		   |
		   V
	fileName->cdev->DA Handler->System

(pardon the sophisticated graphics).  So naturally, GetResource fails if
the only place an 'EXL ' -4048 resource is is in your file fileName.

-Bill Hofmann