How to get contents of a NSTextFieldCell in a cell-based outline when the user quits while editing

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 was:

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.