If you set up an OutlineView in Interface Builder and connect your Controller as its dataSource and delegate (and provide the methods there accordingly), you will notice that
- (id)outlineView:(NSOutlineView *)outlineView
never get’s called. The reason might very simple: in Interface Builder, in the attributes inspector for your OutlineView, you can define the Content Mode as View Based or Cell Based.
If you simply want to display the content of NSStrings, choose Cell Based, and objectValueForTableColumn will be called.
Only took me 3 hours to find out.