使用Cocoa for OS X，Xcode 9.3，Swift 4.1复制视图问题

I am new to programming and trying to learn Cocoa for Mac OS using Xcode 9.3 and Swift 4.1. I’ve worked through books on C++ and Objective-C. Now I am working through the Big Nerd Ranch book, Cocoa Programming for Mac OS, 5th edition which uses Swift 2.0 (on my own). There have been challenges trying to work through the differences from Swift 2.0 to 4.1, and I don’t know if this issue if part of that.I am new to programming and trying to learn Coc