Add view to my UIView used for draw(rect:) - swift

Question

I'm trying to make my own chart thing, so I opened my playground and started typing !
So I've learn how to use, draw(), so far so cool. But now, I'm trying to add some text on it. So here's my code :
import UIKit
class drawGraphMonthly: UIView {
var arrayOfDataPerMonth: [Int]?
var months: [String]?
var goldenRatioForData: CGFloat?
var goldenRationForMonth: CGFloat?
var monthStackView: UIStackView?
init(frame: CGRect, arrayOfDataPerMonth: [Int]) {
super.init(frame: frame)
self.arrayOfDataPerMonth = arrayOfDataPerMonth
self.goldenRatioForData = (frame.size.height / 2) / CGFloat((self.arrayOfDataPerMonth!.max())!)
self.goldenRationForMonth = frame.size.width / CGFloat((self.arrayOfDataPerMonth?.count)!)
self.months = ["J", "F", "M", "A", "M", "J", "J", "A", "S", "O", "N", "D"]
self.monthStackView = {
let sv = UIStackView()
sv.translatesAutoresizingMaskIntoConstraints = false
sv.backgroundColor = .red
sv.distribution = .fillEqually
sv.axis = .horizontal
for month in self.months! {
let monthLabel: UILabel = {
let label = UILabel()
label.text = month
return label
}()
sv.addArrangedSubview(monthLabel)
}
return sv
}()
self.addSubview(monthStackView!)
monthStackView?.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
monthStackView?.leftAnchor.constraint(equalTo: self.leftAnchor).isActive = true
monthStackView?.rightAnchor.constraint(equalTo: self.rightAnchor).isActive = true
monthStackView?.heightAnchor.constraint(equalToConstant: 30).isActive = true
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func draw(_ rect: CGRect) {
// On dessine le background
let backgroundView = UIBezierPath(rect: CGRect(x: frame.size.width, y: frame.size.height, width: 1, height: 1))
let secondPoint = CGPoint(x: 0, y: frame.size.height)
let thirdPointData = getY(y: (arrayOfDataPerMonth?[(arrayOfDataPerMonth?.count)! - 1])!)
let thirdPoint = CGPoint(x: 0, y: thirdPointData)
backgroundView.addLine(to: secondPoint)
backgroundView.addLine(to: thirdPoint)
var countBG = 1
while countBG <= (arrayOfDataPerMonth?.count)! {
let x = CGFloat(countBG) * goldenRationForMonth!
let y = getY(y: (arrayOfDataPerMonth?[countBG - 1])!)
let point = CGPoint(x: x, y: y)
backgroundView.addLine(to: point)
countBG += 1
}
UIColor.white.setFill()
backgroundView.fill()
// On dessine le trait
let line = UIBezierPath(rect: CGRect(x: 0, y: thirdPointData, width: 0, height: 0))
var countLine = 1
while countLine <= (arrayOfDataPerMonth?.count)! {
let x = CGFloat(countLine) * goldenRationForMonth!
let y = getY(y: (arrayOfDataPerMonth?[countLine - 1])!)
let point = CGPoint(x: x, y: y)
line.addLine(to: point)
countLine += 1
}
UIColor.blue.setStroke()
line.lineWidth = 4
line.stroke()
}
func getY(y: Int) -> CGFloat {
var yToReturn : CGFloat = 0
yToReturn = (frame.size.height - (CGFloat(y) * self.goldenRatioForData!)) - 30
return yToReturn
}
}
let array = [21, 34, 36, 33, 31, 27, 23, 19, 8, 5, 25, 14]
let view = drawGraphMonthly(frame: CGRect(x: 0, y: 0, width: 414, height: 250), arrayOfDataPerMonth: array)
view.backgroundColor = UIColor(red:0.20, green:0.20, blue:0.20, alpha:1.0)
You should have the same result as I have if you copy/paste this into a Playground.
So my question is, why is my stackview not showing ?