制成自己的自定义视图类时，视图不出现

Question

I'm making a simple view programatically in Swift and I have this first code that is working just fine:

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .darkGray

        let card:UIView = UIView()
        card.frame = CGRect(x: 38, y: 120, width: 300, height: 300)
        card.backgroundColor = .white
        card.layer.cornerRadius = 10
        card.layer.shadowOpacity = 0.5
        card.layer.shadowOffset = CGSize(width: 0, height: 10)
        card.layer.shadowRadius = 10

        view.addSubview(card)
    }
}

This code make this view:

But I want to reuse the card so I put it into a new class like a custom view, but the card now disappears:

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .darkGray

        let card = Card(frame: CGRect(x: 38, y: 120, width: 300, height: 300))

        view.addSubview(card)
    }
}

class Card:UIView {
    var box:UIView = UIView()

    override init(frame: CGRect) {
        super.init(frame: frame)
        setupLayout()
    }

    func setupLayout(){
        box.backgroundColor = .white
        box.layer.cornerRadius = 10
        box.layer.shadowOpacity = 0.5
        box.layer.shadowOffset = CGSize(width: 0, height: 10)
        box.layer.shadowRadius = 10

        addSubview(box)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

Do you know what is wrong with the second code?

Answer 1

Your box doesn't know where it should be drawn. Add in this one line, which gives it a frame (an origin & size):

func setupLayout(){
    box.backgroundColor = .white
    box.layer.cornerRadius = 10
    box.layer.shadowOpacity = 0.5
    box.layer.shadowOffset = CGSize(width: 0, height: 10)
    box.layer.shadowRadius = 10
    // here's the line to add!
    box.frame = self.frame.insetBy(dx: 10.0, dy: 10.0)
    self.addSubview(box)
}

Answer 2

This is better:

func setupLayout(){
    box.backgroundColor = .white
    box.layer.cornerRadius = 10
    box.layer.shadowOpacity = 0.5
    box.layer.shadowOffset = CGSize(width: 0, height: 10)
    box.layer.shadowRadius = 10

    box.frame = self.frame
    self.addSubview(box)
}

It automatically gets the frame from the initializer.