Re: NSLayoutManager and avoiding widows and orphans

FROM : Ross Carter
DATE : Fri Nov 09 17:32:59 2007

I got widow-orphan protection working by subclassing the 
NSATSTypesetter and overriding beginParagraph, 
willSetLineFragmentRect:forGlyphRange:usedRect:baselineOffset:, and 
endParagraph. It was kind of complicated, and I don't have the code 
here, and frankly I don't remember how thoroughly I debugged it before 
setting the project aside.

Basically, instead of modifying the text container height, I used 
those methods to test for a widow/orphan condition and if true set a 
variable specifying the first glyph that should be thrown to the next 
container. In endParagraph, if that variable is set, I forced relayout 
and on the next pass through
willSetLineFragmentRect:forGlyphRange:usedRect:baselineOffset: I 
increased the the height of lineRect and usedRect so the typesetter on 
its own would throw the line to the next container.

It was complicated because I had to turn off textView drawing to 
eliminate flicker during relayout, but you might be able to figure out 
a better implementation of this idea.

Ross

On Nov 7, 2007, at 6:06 PM, Keith Blount wrote:

> Hi Martin,
>
>
> Thanks for your help (again). Unfortunately, no, this frame 
> adjustment isn't triggered from the delegate methods - I tried to 
> shift everything out of there for the exact reasons you describe. 
> The only thing I do in the delegate method is make note of whether I 
> *need* to adjust the frame. Then I wait for all layout to finish, 
> and only once that's done do I adjust the frame. Then I trigger all 
> layout again, at the end of which I check to see if another 
> adjustment is needed. This goes on until the delegate method doesn't 
> return any more adjustments to be made. But I'm careful not to 
> trigger any extra layout from within the delegate method. The hang 
> happens when the frame change forces the delegate method to add 
> another page. For some reason, this seems to cause everything to go 
> crazy, but I'm not sure why...
>
>
> Right now I may just have to scrap widow and orphans support from 
> printing in my app altogether. The layout manager just seems too 
> delicate, triggering hangs and crashes that are incredibly difficult 
> to track down.
>
>
> Thanks again and all the best,
> Keith
>
> ----- Original Message ----
> From: Martin Wierschin <<email_removed>>
> To: Keith Blount <<email_removed>>
> Cc: <email_removed>
> Sent: Wednesday, November 7, 2007 1:24:04 AM
> Subject: Re: NSLayoutManager and avoiding widows and orphans
>
>
> Hi Keith,
>
> So, next I tried waiting until all layout is complete and then 
> enumerating through the text containers, checking for a widow or 
> orphan at the end of each one, adjusting the frame and then forcing 
> layout. But again, if a page gets added because of this, we hit 
> problems - bounds and run storage exceptions, and problems caused by 
> adding a text container whilst enumerating through the text 
> containers.
>
>
> Do you trigger this frame adjusting from the NSLayoutManager 
> delegate methods? In my experience it is not safe to modify text 
> container geometry/size from this callback. Try this and see if it 
> fixes your crash: after you detect that layout has completed 
> schedule your fixing code via 
> "performSelector:withObject:afterDelay:".
>
>
> ~Martin
>
>
>
>
>
>
>
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