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From: jackiw@cs.swarthmore.edu (Nick Jackiw)
Newsgroups: comp.sys.mac.programmer
Subject: Re: MultiFinder questions
Message-ID: <2665@carthage.cs.swarthmore.edu>
Date: 11 Apr 89 01:35:53 GMT
References: <42072@csvax1.cs.tcd.ie>
Reply-To: jackiw@carthage.UUCP (Nick Jackiw)
Organization: Visual Geometry Project, Swarthmore College, PA
Lines: 53

In article <42072@csvax1.cs.tcd.ie> fmodwyer@csvax1.cs.tcd.ie (Frank O'Dwyer, Dept. of Computer Science, TCD, Dublin 2, IRELAND) writes:
> 1. When can an application background under MF?  i.e., when is it
> O.K. to set the 'Can Background' bit in the MF SIZE resource?

Anytime.  CanBackground really only seems to be used to determine whether
the application should get null events while it's in the background (on
which it should "process-one-null-event's-worth").  It'll get update
events for its windows regardless of whether it CanBackground or not. 

> 2. What does an application have to do to be 'MultiFinder Aware'?

You should understand suspend and resume events (which are both appl4
events; Suspend has bit#0 of theEvent.message clear; Resume has bit#0
set.  What does it mean to "understand" these events?  Two things: you
should deactivate your topmost window, get rid of all hi-liting, etc.
Second, if you keep the content of the clipboard in some private format
(instead of using the actual DeskScrap), for efficiency's sake lets say,
and actually put it onto the deskScrap only when User asks for a desk
accessory or quits (intending, presumably, to PASTE it into some application
which doesn't parse your internal format), then you want to normalize
your scrap (convert to desk scrap) on suspend. Resume requires only
reactivation of the window, generally speaking.

If you don't set Multifinder Aware, Multifinder goes through a long
song-and-dance of trying to convince your application that it's about to
see a desk accessory (based on the assumption that your app will respond
in more or less the ways outlined in the previous paragraph).

> I ask because I've written a program which seems to background fine
> under MF - even though I've set 'MultiFinder Aware' to false,
> and set 'Can Background' to true - *without* making the slightest
> provision in my code to handle backgrounding.  Is this O.K. or
> is my program doomed to crash under some wierd set of circumstances? 

Your program is merrily getting null events (canBackground), which I
assume it interprets as a signal to do-some-more-processing.  Fine, you
won't crash.  Adding code to understand Suspend&Resume events, and then
setting MultiFinderAware, will speed up your program's response to being
switched out.  If it seems to work fine now, you probably don't need to
worry about being (technically) MultifinderAware.

> -- 
> Frank O'Dwyer,                            e-mail: FMODWYER@cs.tcd.ie
> Dept. of Computer Science,
> Trinity College Dublin,
> IRELAND.


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