Updating progress bar from multiple nested functions - best way?

FROM : Johnny Deadman
DATE : Mon Apr 18 14:45:55 2005

They say if you are finding something difficult in Cocoa you are 
doing it wrong so so... I probably am.

I have an autoformat routine for my screenplays which is complicated 
and takes a while. When the user chooses 'autoformat', the format 
manager creates a parser which parses the screenplay, which in turn 
splits it into paragraphs, normalizes the text, performs context-free 
and context-dependent analysis, builds a structure representing the 
screenplay, and passes it back to the format manager, which replaces 
the appropriate text and applies the appropriate formatting.

I want to put up a progress indicator BUT the process is split up 
between many independent objects which don't know about each other 
and don't know whether the job they're doing (eg formatting a 
paragraph, analysing a scene) is a one-shot or part of a bigger picture.

Moreover, the whole process is handled by an object (the format 
manager) which philosophically I do not feel should handle any 
interaction. It might, for example, be called in the absence of a UI 
and do its job perfectly well. (It's invoked in turn from an IBAction 
in the main editor window's controller).

So what is the best way to handle a progress bar in this case?

It seems wrong to have to pass each object a reference to the 
progress bar, the proportion of the task completed, and the 
proportion of the task they are responsible for. It seems equally 
wrong to insist that each object retain a reference to the top-level 
object and notify it. I feel they should be agnostic about the 
context from which they are invoked.

--
John Brownlow
Deep Fried Films, Inc

http://www.johnbrownlow.com
http://www.pinkheadedbug.com