swift - 以编程方式将约束添加到 Storyboard 上的现有 View

Question

我发现当以编程方式键入 Storyboard上的现有 View 时，约束没有实现纠正。这是我所拥有的:

class ViewController: UIViewController {

    @IBOutlet weak var textField2: UITextField! {
        didSet {
            textField2.delegate = self
        }
    }

    func viewDidLoad() {
        super.viewDidLoad()

        let superview = self.view

        let textField1 = UITextField()
        textField1.backgroundColor = UIColor.greenColor()
        textField1.placeholder = "test text field"
        view.addSubview(textField1)
        textField1.translatesAutoresizingMaskIntoConstraints = false
        superview.addConstraint(NSLayoutConstraint(item: textField1, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .Width, multiplier: 1, constant: superview.frame.width * 0.50))
        superview.addConstraint(NSLayoutConstraint(item: textField1, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .Height, multiplier: 1, constant: superview.frame.height * 0.05))
        superview.addConstraint(NSLayoutConstraint(item: textField1, attribute: .CenterX, relatedBy: .Equal, toItem: superview, attribute: .CenterX, multiplier: 1, constant: 0))
        superview.addConstraint(NSLayoutConstraint(item: textField1, attribute: .CenterY, relatedBy: .Equal, toItem: superview, attribute: .CenterY, multiplier: 1, constant: 0))

        textField2.translatesAutoresizingMaskIntoConstraints = false
        superview.addConstraint(NSLayoutConstraint(item: textField2, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .Width, multiplier: 1, constant: superview.frame.width * 0.50))
        superview.addConstraint(NSLayoutConstraint(item: textField2, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .Height, multiplier: 1, constant: superview.frame.height * 0.05))
        superview.addConstraint(NSLayoutConstraint(item: textField2, attribute: .CenterX, relatedBy: .Equal, toItem: superview, attribute: .CenterX, multiplier: 1, constant: 0))
        superview.addConstraint(NSLayoutConstraint(item: textField2, attribute: .CenterY, relatedBy: .Equal, toItem: superview, attribute: .CenterY, multiplier: 1, constant: 0))

    }
}

textField1 工作完美。它被添加到 View 的中心。但是，我拖放到 Storyboard 上的 textField2 偏离了中心。为什么会发生这种情况？

谢谢

Answer 1

问题是，如果 View 来自 Storyboard，例如您的 textField2，它已经有约束。说 textField2.translatesAutoresizingMaskIntoConstraints = false 并不能神奇地解决这个问题。您还需要以某种方式掌握这些约束，并在代码中应用您自己的约束之前删除它们。这可能很难做到，而你却没有这样做，这就是为什么你的观点行为不当。在这个阶段，您最好遵循以下简单规则:

• 如果 View 来自 Storyboard，则仅在 Storyboard中设置其约束

• 但是如果 View 是用代码创建的，现在您可以说 translatesAutoresizingMaskIntoConstraints = false 并在代码中设置其约束