UIKit:如何将多个CALayers混合到一个视图层中？

import UIKit

class CustomView: UIView {
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupLayers()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setupLayers()
    }
    
    private func setupLayers() {
        let layer1 = CALayer()
        layer1.backgroundColor = UIColor.red.cgColor
        layer1.frame = CGRect(x: 0, y: 0, width: 100, height: 100)
        
        let layer2 = CALayer()
        layer2.backgroundColor = UIColor.blue.cgColor
        layer2.frame = CGRect(x: 50, y: 50, width: 100, height: 100)
        
        let layer3 = CALayer()
        layer3.backgroundColor = UIColor.green.cgColor
        layer3.frame = CGRect(x: 100, y: 100, width: 100, height: 100)
        
        layer.addSublayer(layer1)
        layer.addSublayer(layer2)
        layer.addSublayer(layer3)
    }
}