在 swift 5 中更新约束

Question

我试过停用和重新激活...但是我似乎无法找到如何去做...我有代码可以用作示例但它总是让我失败，如果有人知道如何更新约束在 swift 5 请让我知道...我知道 updateConstraint() 存在只是不确定如何使用它。

let constraint1: NSLayoutConstraint? = text.bottomAnchor.constraint(equalTo: view.bottomAnchor)

let constraint2: NSLayoutConstraint? = text.bottomAnchor.constraint (equalTo: view.bottomAnchor, constant: 5)

if acondition {
constraint1?.isActive = false
constraint2.isActive = true
} else {
constraint2.isActive = false
constraint1.isActive = true
}

Answer 1

也许你可以检查你的 @properties 并将 weak 替换为 strong。原因是，isActive = false 将设置 self.yourConstraint = nil，因此您将无法再次使用 self.yourConstraint。

Answer 2

首先声明变量，将启动约束变量设置为 true 并调用激活和禁用约束的函数后，尝试使用我的示例：

在控制器下 class 声明一个按钮和一个要移动的视图：

let dummyView = UIView()
let button = UIButton(type: .system)

在声明变量后以约束移动视图：

var up: NSLayoutConstraint?
var down: NSLayoutConstraint?

在 ViewDiLoad 中像这样设置视图、按钮和约束：

dummyView.backgroundColor = .yellow
    dummyView.translatesAutoresizingMaskIntoConstraints = false

    button.setTitle("viewDiwn", for: .normal)
    button.backgroundColor = .red
    button.setTitleColor(.white, for: .normal)
    button.titleLabel?.font = .systemFont(ofSize: 16)
    button.addTarget(self, action: #selector(handletapButton), for: .touchUpInside)// button action that call handletapButton func
    button.translatesAutoresizingMaskIntoConstraints = false

    view.addSubview(dummyView)
    up = dummyView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor)
    up?.isActive = true // start constraint active
    down = dummyView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 100) // constraint to activate for move the view

    dummyView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
    dummyView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
    dummyView.heightAnchor.constraint(equalToConstant: 50).isActive = true

    view.addSubview(button)
    button.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
    button.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
    button.heightAnchor.constraint(equalToConstant: 50).isActive = true
    button.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true

现在编写通过约束动画移动视图的函数：

@objc func handletapButton() {
    UIView.animate(withDuration: 0.5, delay: 0, options: .curveEaseOut, animations: {
        self.up?.isActive = false
        self.down?.isActive = true
        self.view.layoutIfNeeded()
    }, completion: nil)
}

这是结果

在 swift 5 中更新约束

Updating constraints in swift 5

swift

swift5

xcode11.4