我尝试使用 constraintEqualToAnchor() 设置一个带有 AutoLayout 约束的 View :

override func viewDidLoad() {
    super.viewDidLoad()

    let myView = UIView()
    myView.backgroundColor = UIColor.orangeColor()
    myView.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(myView)

    myView.leftAnchor.constraintEqualToAnchor(view.leftAnchor).active = true
    myView.trailingAnchor.constraintEqualToAnchor(view.trailingAnchor).active = true
    myView.topAnchor.constraintEqualToAnchor(view.topAnchor).active = true
    myView.bottomAnchor.constraintEqualToAnchor(view.bottomAnchor).active = true

    /******************************************/
    /* I try to change one of the constraints */
    /******************************************/
    myView.leftAnchor.constraintEqualToAnchor(view.rightAnchor, constant: -100).active = true  
}

在最后一行代码中，我尝试更改其中一个约束。我认为它会起作用，但它在控制台日志中给出了一些错误

"<NSLayoutConstraint:0x7fb53a5180d0 H:|-(0)-[UIView:0x7fb53a5190b0](LTR)   (Names: '|':UIView:0x7fb53a519240 )>",
"<NSLayoutConstraint:0x7fb53a51f660 H:[UIView:0x7fb53a519240]-(-100)-[UIView:0x7fb53a5190b0](LTR)>",
"<NSLayoutConstraint:0x7fb53a711ee0 'UIView-Encapsulated-Layout-Width' H:[UIView:0x7fb53a519240(414)]>"

使用 constraintEqualToAnchor()? 时，设置约束后更改约束的正确方法是什么？

最佳答案

您需要在激活一个新约束时停用之前的约束，这样您就不会过度约束您的 View 。为此，将对每个约束的引用作为属性存储在 ViewController 中，然后将旧约束的 active 属性设置为 false 在创建和激活新约束之前:

swift 2.x:

class ViewController: UIViewController {
    var leftConstraint: NSLayoutConstraint?
    var trailingConstraint: NSLayoutConstraint?
    var topConstraint: NSLayoutConstraint?
    var bottomConstraint: NSLayoutConstraint?

    override func viewDidLoad() {
        super.viewDidLoad()

        let myView = UIView()
        myView.backgroundColor = UIColor.orangeColor()
        myView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(myView)

        leftConstraint = myView.leftAnchor.constraintEqualToAnchor(view.leftAnchor)
        leftConstraint?.active = true

        trailingConstraint = myView.trailingAnchor.constraintEqualToAnchor(view.trailingAnchor)
        trailingConstraint?.active = true

        topConstraint = myView.topAnchor.constraintEqualToAnchor(view.topAnchor)
        topConstraint?.active = true

        bottomConstraint = myView.bottomAnchor.constraintEqualToAnchor(view.bottomAnchor)
        bottomConstraint?.active = true

        /******************************************/
        /* I try to change one of the constraints */
        /******************************************/
        leftConstraint?.active = false
        leftConstraint = myView.leftAnchor.constraintEqualToAnchor(view.rightAnchor, constant: -100)
        leftConstraint?.active = true
    }
}

Swift 3 语法更新:

class ViewController: UIViewController {
    var leftConstraint: NSLayoutConstraint?
    var trailingConstraint: NSLayoutConstraint?
    var topConstraint: NSLayoutConstraint?
    var bottomConstraint: NSLayoutConstraint?

    override func viewDidLoad() {
        super.viewDidLoad()

        let myView = UIView()
        myView.backgroundColor = UIColor.orange
        myView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(myView)

        leftConstraint = myView.leftAnchor.constraint(equalTo: view.leftAnchor)
        leftConstraint?.isActive = true

        trailingConstraint = myView.trailingAnchor.constraint(equalTo: view.trailingAnchor)
        trailingConstraint?.isActive = true

        topConstraint = myView.topAnchor.constraint(equalTo: view.topAnchor)
        topConstraint?.isActive = true

        bottomConstraint = myView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
        bottomConstraint?.isActive = true

        /******************************************/
        /* I try to change one of the constraints */
        /******************************************/
        leftConstraint?.isActive = false
        leftConstraint = myView.leftAnchor.constraint(equalTo: view.rightAnchor, constant: -100)
        leftConstraint?.isActive = true
    }
}

关于ios - 使用 constraintEqualToAnchor() 时如何在设置自动布局约束后更改它们？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/34391732/