Swift:以编程方式将自动布局约束从一个 View 复制到另一个 View

Question

我有一个 UIButton，我在 Storyboard中设置了自动布局约束。我还有一个 UIView，我在 UIViewController 的 viewDidLoad 方法中启动它。我使此 View 具有(几乎)所有与 UIButton 相同的属性，但是当我在模拟器中运行它时，它不会“粘”在按钮上。这是我所拥有的:

class ViewController: UIViewController {

    @IBOutlet weak var someButton: UIButton!

    func viewDidLoad() {
        super.viewDidLoad()

        let someView = UIView()
        someView.backgroundColor = UIColor.greenColor()
        someView.frame = someButton.bounds
        someView.frame.origin = someButton.frame.origin
        someView.autoresizingMask = someButton.autoresizingMask
        someView.autoresizesSubviews = true
        someView.layer.cornerRadius = someButton.layer.cornerRadius
        someView.clipsToBounds = true
        someView.userInteractionEnabled = false
        view.insertSubview(someView, belowSubview: someButton)
    }

}

我想我缺少 someView.auto 布局约束？

编辑:我认为访问 UIButton 的约束会起作用，但它们似乎是一个空数组。 Storyboard约束是否被隐藏？

someView.addConstraints(someButton.constraints)

谢谢。

Answer 1

以这种方式复制约束失败，因为:

• Storyboard中的约束被添加到父 View 而不是按钮本身
• 您尝试复制的约束引用的是按钮而不是您的新 View

与其复制约束，不如保持简单并创建新约束并引用按钮:

    let someView = UIView()
    someView.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(someView)

    view.addConstraints([
        NSLayoutConstraint(item: someView, attribute: .Leading, relatedBy: .Equal, toItem: someButton, attribute: .Leading, multiplier: 1, constant: 0),
        NSLayoutConstraint(item: someView, attribute: .Trailing, relatedBy: .Equal, toItem: someButton, attribute: .Trailing, multiplier: 1, constant: 0),
        NSLayoutConstraint(item: someView, attribute: .Top, relatedBy: .Equal, toItem: someButton, attribute: .Top, multiplier: 1, constant: 0),
        NSLayoutConstraint(item: someView, attribute: .Bottom, relatedBy: .Equal, toItem: someButton, attribute: .Bottom, multiplier: 1, constant: 0)
    ])