My revisions to DragAndDropOutlineEdit

FROM : George Orthwein
DATE : Thu Jul 06 22:00:05 2006

So I went back to take another look at the tree controller/outline 
view problems I had been putting off and... I *think* I might 
actually have a working NSTreeController + Core Data + 
NSOutlineView!!! (*knock on wood*)
http://home.comcast.net/~george.o/DragAndDropOutlineEdit.html

I started with Matt Holiday's DragAndDropOutlineEdit (http://
homepage.mac.com/matthol2/cocoa/page1/page1.html) and:
- added Count Key Path to avoid errors when dragging multiple items.
- added a "displayOrder" attribute to save ordering.
- added an "isExpanded" attribute to save/restore expansion states 
even after Undo/Redo (mostly).
- added Undo action names.
- added some support for a max depth level.
- moved the outline code out of MyDocument and into 
MyOutlineViewController so the project can be used as a template easier.

One little flaw though... I had to use a posing hack found on 
cocoadev.com in order to solve certain errors I was getting on Undo:
http://www.cocoadev.com/index.pl?NSTreeControllerBugOrDeveloperError 
(from "Frank" near the bottom)

The posing seems to work great (so thanks Frank!) but I'm a little 
unsure to resort to such a thing. I'd be interested if anyone can 
recommend a better workaround. Perhaps there is a particular 
NSTreeController method to override? I'm probably grasping at straws 
here, but I don't really want to get into writing a tree controller 
from scratch (not sure I'd even know where to begin with that).

The easiest way I found to trigger the error was usually:
1) create a bunch of items with the New button
2) drag some (at least 3) to another to make them children
3) drag some (at least 2 but not all) of those children to another 
top level item
4) Undo and then Redo
If you comment out the posing in windowControllerDidLoadNib, the 
above will trigger an error.

So anyone who desires, please download and, ahem, try to break it. 
And anyone who can find a better workaround than the class posing, or 
has some other improvement, please share. I really think the 
community needs a working OutlineView + ordered Core Data template to 
fill the void until 10.5 comes along.

Thanks,
George