The previous version of this question was closed because the moderator did not recognize that this is a cell-based Outline not a view-based outline. The answer the moderator suggested does not work for a cell-based outline.
The question as previously asked is:
I have a cell-based NSOutlineView. How do I get the contents of the NSTextFieldCell when the user Quits the app while editing that cell. Currently, attributedStringValue returns the contents before editing began.