I am following a personal learning path for macOS development, learning the basics of C and Objective-C before moving on to Swift (which I already know a bit, but felt the need to learn where all that came from). I am aware there are better, more modern and functional APIs, so please do not suggest learning that or SwiftUI. The point of this question is knowing what is not working in my example.
I closely followed

I understand part of this error, but do not know how to "register one item nib or class", while dataSource is not covered in this tutorial.
Comparing with the source code I noticed that an extra outlet was added from the Collection View, connecting its itemPrototype to the CollectionViewItem. I did just that and, this time, Xcode refused to build throwing this error:
Do you know how to make this work? I would also appreciate any and every explanation on the first error.
Thank you for your patience and help.

CodePudding user response：

NSOutlineView changed quite a bit in macOS 10.11 and isn't compatible with the tutorial. NSOutlineView can be used in legacy mode by choosing layout Content Array (Legacy) in IB.