如何在Xcode中为iPhone SDK构建自定义控件？

import UIKit

@IBDesignable class CustomButton: UIButton {
    @IBInspectable var cornerRadius: CGFloat = 0 {
        didSet {
            layer.cornerRadius = cornerRadius
        }
    }

    @IBInspectable var borderWidth: CGFloat = 0 {
        didSet {
            layer.borderWidth = borderWidth
        }
    }

    @IBInspectable var borderColor: UIColor = UIColor.clear {
        didSet {
            layer.borderColor = borderColor.cgColor
        }
    }
}

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var customButton: CustomButton!

    override func viewDidLoad() {
        super.viewDidLoad()
        customButton.cornerRadius = 10
        customButton.borderWidth = 2
        customButton.borderColor = UIColor.blue
    }
}