Hello,
I was working through this tutorial https://developer.xamarin.com/guides/mac/user-interface/working-with-collection-views and was unable to get it to work. I was getting the following runtime error: "-[NSNib _initWithNibNamed:bundle:options:] could not load the nibName: EmployeeItemController in bundle (null)."
I got it working eventually, and I believe the problem was the following part of the instructions. In "Creating the Cell Prototype" we are directed to create a new ViewController with the name EmployeeItem, and we're told that "This will add an EmployeeItem.cs, EmployeeItemController.cs and EmployeeItemController.xib file to the project's solution." That is not true: what you get are the three files EmployeeItem.cs, EmployeeItemController.cs and, crucially, EmployeeItem.xib. You must manually rename the .xib file to be EmployeeItemController.xib.
Hopefully this helps others.