playground.swift

//: [Previous](@previous)
import AppKit
import XCPlayground

extension NSLayoutConstraint {
    convenience init(view item: NSView, to toItem: NSView, attribute: NSLayoutAttribute, constant c: CGFloat = 0) {
        self.init(item: item, attribute: attribute,
                  relatedBy: .Equal,
                  toItem: toItem, attribute: attribute,
                  multiplier: 1.0, constant: c)
        self.active = true
        self.shouldBeArchived = true
        item.translatesAutoresizingMaskIntoConstraints = false
    }
}

let viewRect = NSRect(x: 0, y: 0, width: 300, height: 200)
var view = NSView(frame: viewRect)

view.wantsLayer = true
view.layer?.backgroundColor = NSColor.windowBackgroundColor().CGColor

class test: NSObject {
    @objc func test(sender: AnyObject) {
        print("Hallo")
    }
}

let t = test()
var button: NSButton = {
    $0.title = "Hallo"
    $0.target = t
    $0.action = #selector(test.test(_:))
    $0.enabled = true
    $0.bezelStyle = .RoundedBezelStyle
    return $0
}(NSButton(frame: NSRect(x: 0, y: 0, width: 100, height: 30)))

view.addSubview(button)

XCPlaygroundPage.currentPage.liveView = view
NSLayoutConstraint(view: button, to: view, attribute: .CenterX)
NSLayoutConstraint(view: button, to: view, attribute: .CenterY)

Hey, awesome example!

Forked it and updated it to swift 3.0

https://gist.github.com/eonist/75b752a5abcd472e6781d6a0c12f6919

@eonist Good job