Path: utzoo!attcan!uunet!snorkelwacker!usc!ucsd!helios.ee.lbl.gov!ux1.lbl.gov!beard
From: beard@ux1.lbl.gov (Patrick C Beard)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Trap patch questions
Message-ID: <5755@helios.ee.lbl.gov>
Date: 7 Jun 90 17:44:11 GMT
References: <1101@haydn.nsc.com>
Sender: usenet@helios.ee.lbl.gov
Reply-To: beard@ux1.lbl.gov (Patrick C Beard)
Organization: Berkeley Systems, Inc.
Lines: 45
X-Local-Date: 7 Jun 90 10:44:11 PDT

In article <1101@haydn.nsc.com> mcdan@dtg.nsc.com (Eric McDaniel) writes:
#Reply-To: mcdan@dtg.nsc.com
#Distribution: 
#
#I am trying to write a patch to display a dialog box
#under certain circumstances when an application is
#launched, and am having a few problems:
#
#1.  At first I tried patching the _Launch and _Chain
#traps, but some launching utilities (notably OnCue)
#apparently don't use these traps, as my code was not
#always executed.  I now patch _LoadSeg and check if
#the segment number being loaded is #1 before calling
#my code. It works, but seems less efficient since _LoadSeg
#can be called any number of times within an application.

This is an adequate solution.  In fact MultiFinder itself doesn't use
the Launch trap.

#2.  When I call ShowWindow to display the dialog box,
#I consistently get some sort of system error.  I checked
#the DialogPtr and all associated handles, and everything
#seems to be valid and on the system heap.  I'm guessing
#the problem has something to do with setting up A5 or
#the GrafPort correctly.

You got it.  You have to perform the standard litany of manager
initialization calls, including InitGraf, InitWindows, etc.  It doesn't
seem to be a problem to do this and then have the application do it
again.


#Could my use of a 'tail-patch' be the problem, and if
#so, how else could I write this thing?

A tail patch is probably not a problem, but it is also probably unnecessary
for what you are trying to do.  A simple head patch of LoadSeg would be
adequate.

Good luck!

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-  Patrick Beard, Macintosh Programmer                        (beard@lbl.gov) -
-  Berkeley Systems, Inc.  ".......<dead air>.......Good day!" - Paul Harvey  -
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