(self asking and self-answering because I spent hours on the web looking for this, and most of the resources all say "I solved it in the end" without giving an explanation)

I had a very simple Core Data + Bindings application:

  • An NSArrayController pulling items out of Core Data
  • An NSTableView rendering them
  • Another NSTableView that when you click on a row in the first table, displays the details of that item

Item 3 above was causing application crash, with the error:

[(my NSManagedObject) copyWithZone:]: unrecognized selector sent to instance

Implementing that method (!) and putting a breakpoint there, I found it was being invoked by Apple's NSCell class - this didn't much help :(.

cocoa core-data cocoa-bindings nsmanagedobject
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