Swift: Popover tooltip from button in iOS

ButtonTooltip.swift

import UIKit

class ViewController: UIViewController {
    
    var label:ToolTip!
    var labelTransform:CGAffineTransform!
    let buttonHeight:CGFloat = 100
    let buttonWidth:CGFloat = 200
   
    override func viewDidLoad() {
        super.viewDidLoad()

        let button = UIButton()
        button.setTitle("Push Me", forState: .Normal)
        button.addTarget(self, action: Selector("buttonPushed"), forControlEvents: .TouchUpInside)
        button.backgroundColor = UIColor.orangeColor()
        view.addSubview(button)
        button.translatesAutoresizingMaskIntoConstraints = false
        button.centerXAnchor.constraintEqualToAnchor(view.centerXAnchor).active = true
        button.centerYAnchor.constraintEqualToAnchor(view.centerYAnchor).active = true
        button.heightAnchor.constraintEqualToConstant(buttonHeight).active = true
        button.widthAnchor.constraintEqualToConstant(buttonWidth).active = true
        
        label = ToolTip()
        
        view.insertSubview(label, belowSubview: button)
        label.translatesAutoresizingMaskIntoConstraints = false
        label.heightAnchor.constraintEqualToConstant(buttonHeight).active = true
        label.widthAnchor.constraintEqualToConstant(buttonWidth).active = true
        
        
        label.bottomAnchor.constraintEqualToAnchor(button.topAnchor).active = true
        label.centerXAnchor.constraintEqualToAnchor(view.centerXAnchor).active = true
        label.text = "This button is orange!"
        label.textColor = UIColor.whiteColor()
        label.textAlignment = .Center
        let trans1 =  CGAffineTransformMakeScale(0, 0)
        let trans2 =  CGAffineTransformMakeTranslation(0, buttonHeight)
        labelTransform = CGAffineTransformConcat(trans1, trans2)
        label.transform = labelTransform
        
    }
    
    func buttonPushed() {
        
        if label.transform.ty > 0 {
            UIView.animateWithDuration(0.75, delay: 0, usingSpringWithDamping: 0.7, initialSpringVelocity: 0.5, options: .CurveEaseInOut, animations: { () -> Void in
                
                self.label.transform = CGAffineTransformIdentity
                
                }, completion:    nil)
            
        }
        else {
            UIView.animateWithDuration(0.5, delay: 0, options: .CurveEaseInOut, animations:  { () -> Void in
                self.label.alpha = 0
                
                }, completion:    {_ in
                    self.label.transform = self.labelTransform
                    self.label.alpha = 1
            })        }
        
        
        
    }
    
}

class ToolTip: UILabel {
    var roundRect:CGRect!
    override func drawTextInRect(rect: CGRect) {
        super.drawTextInRect(roundRect)
    }
    override func drawRect(rect: CGRect) {
        roundRect = CGRect(x: rect.minX, y: rect.minY, width: rect.width, height: rect.height * 4 / 5)
        let roundRectBez = UIBezierPath(roundedRect: roundRect, cornerRadius: 10.0)
        let triangleBez = UIBezierPath()
        triangleBez.moveToPoint(CGPoint(x: roundRect.minX + roundRect.width / 2.5, y:roundRect.maxY))
        triangleBez.addLineToPoint(CGPoint(x:rect.midX,y:rect.maxY))
        triangleBez.addLineToPoint(CGPoint(x: roundRect.maxX - roundRect.width / 2.5, y:roundRect.maxY))
        triangleBez.closePath()
        roundRectBez.appendPath(triangleBez)
        let bez = roundRectBez
        UIColor.lightGrayColor().setFill()
        bez.fill()
        super.drawRect(rect)
    }
}

This code was written in response to a StackOverflow question. I'm posting it here to keep my own record.