An Xcode playground showing a custom UIView

CustomUIViewPlayground.swift

import UIKit
import XCPlayground

class MyView: UIView {
    override init(frame: CGRect) {
        super.init(frame: frame)
        setup()
    }
    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setup()
    }
    override func drawRect(rect: CGRect) {
        let path = UIBezierPath()
        path.moveToPoint(CGPoint(x: 10, y: 10))
        path.addLineToPoint(CGPoint(x: 100,y: 10))
        path.addLineToPoint(CGPoint(x: 100,y: 100))
        path.addLineToPoint(CGPoint(x: 10, y: 100))
        path.closePath()
        UIColor.redColor().setStroke()
        path.lineWidth = 3
        path.stroke()
    }
    
    func setup() {
        backgroundColor = UIColor.whiteColor()
    }
}

let myView = MyView(frame: CGRect(x: 0, y: 0, width: 200, height: 300))

XCPShowView("Demo Square", myView)