Drag and drop single cell in a table/matrix

FROM : Dan Waltin
DATE : Thu Feb 28 23:14:53 2008

Hi all,

The short question is: how do I drag'n'drop single cells in an 
NSTableView (or NSOutlineView). I.e. I don't want the entire row to be 
dragged, just one cell.

Is there any example code on how to do this? Or is there anyone who 
might push me in the right direction? Is 
tableView:shouldTrackCell:forTableColumn:row: something I should learn 
more about? Or is writeRowsWithIndexes what I want?

I googled myself dizzy but haven't found an answer. The NSMatrix class 
looks promising, but I need different column widths as well as 
headers. The NSTableView also looks promising, but dragging seems very 
"row based".

A little more information about the situation: I have a model which 
(simplified) looks like this: there is an Area entity and a Type 
entity and finally an Item entity. The Area and Type entities have a 
title property.

Each Item belongs to exactly one Area and one Type

Item <<----> Area
Item <<----> Type

There might or might not be an Item for a specific Area/Type 
combination.

There is no (explicit) relation between Area and Type. I would like to 
present this in a "matrix" (NSTableView, NSMatrix, or ???) with Area-s 
going vertical and Type-s going horizontal. Like this (monospaced font 
probably required...):

  | Type1  | Type2  |
------+---------+--------+
Area1 |  Item11 |        |
------+---------+--------+
Area2 |        | Item22 |
------+---------+--------+
Area3 |  Item31 | Item32 |
------+---------+--------+

And now the tricky part, there might be a relation between two Item-s. 
This relation is defined by the user and I would like to implement 
this with drag and drop. Of course I could use a context menu, but 
drag and drop feels much more "mac-like" and elegant.

So, for creating a relation between Item11 and, say, Item32, the user 
drag and drops the *cell* Item11 on the cell Item32.

Thanks
/Dan