以编程方式更新约束？

Question

我有一个 UIView 的子类，我想操作一个约束但它不起作用。

按下按钮时 exchangesViewActivated 发生变化并调用函数。

var exchangesViewActivated = false {
    didSet {
        if exchangesViewActivated == true {
            setExchangesView()
        } else {
            setUpLayout()
        }
    }
}

Die 子视图和 translatesAutoresizingMaskIntoConstraints 已设置。

func setUpLayout() {

    bottomContainer.heightAnchor.constraint(equalToConstant: 500).isActive = true


    bottomContainer.leadingAnchor.constraint(equalTo: scrollViewContrainer.leadingAnchor).isActive = true
    bottomContainer.trailingAnchor.constraint(equalTo: scrollViewContrainer.trailingAnchor).isActive = true
    bottomContainer.topAnchor.constraint(equalTo: configBar.bottomAnchor).isActive = true
    bottomContainer.bottomAnchor.constraint(equalTo: scrollViewContrainer.bottomAnchor).isActive = true

}

现在我想通过调用这个函数来操纵约束：

 func setExchangesView() {

bottomContainer.bottomAnchor.constraint(equalTo: scrollViewContrainer.bottomAnchor).isActive = false

        bottomContainer.heightAnchor.constraint(equalToConstant: 500).isActive = false
        bottomContainer.bottomAnchor.constraint(equalTo: self.bottomAnchor, constant: 0).isActive = true
}

但此约束保持激活状态：

bottomContainer.heightAnchor.constraint(equalToConstant: 500).isActive

我错过了什么吗？将约束设置为 false 以停用它还不够吗？我必须打电话给其他人吗？

Answer 1

这不会停用旧的约束，因为它会停用新创建的约束

var heightCon:NSLayoutConstraint!
var botCon:NSLayoutConstraint!

//

heightCon = bottomContainer.heightAnchor.constraint(equalToConstant: 500)
heightCon.isActive = true

botCon = bottomContainer.bottomAnchor.constraint(equalTo: scrollViewContrainer.bottomAnchor)
botCon.isActive = true

然后您可以轻松引用约束并停用它们并添加新约束

Answer 2

setUpLayout() 会在您每次调用 setUpLayout() 方法时添加新的约束。您必须保存约束参考并在下次更新它。

例如

// class variable 
var bottomConstraint:NSLayoutConstraint? = nil

bottomConstraint = bottomContainer.heightAnchor.constraint(equalToConstant: 500)
bottomConstraint.isActive = true

稍后更新约束

bottomConstraint.constant = 100
bottomConstraint.isActive = true

以编程方式更新约束？

Updating Constraints programmatically?

swift

autolayout

constraints

programmatically