Question

我有一个UIView的子类，我想操纵一个约束，但它不起作用。

当按下按钮时，交换ViewActivated更改并调用函数。

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

}

设置子视图和translatesAutoresizingMaskIntoConstraints。

 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
}

现在我想通过调用这个函数来操纵约束：

{{1}}

但是这个约束仍然被激活：

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

我错过了什么吗？将约束设置为false以停用它是不够的？我还需要打电话吗？

Answer 1

这不会停用旧约束，因为它会停用新创建的约束，所以

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

每次调用setUpLayout()方法时，

setUpLayout()都会添加新约束。您必须保存约束引用并在下次更新它。

例如。

// class variable 
var bottomConstraint:NSLayoutConstraint? = nil

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

以后更新约束

bottomConstraint.constant = 100
bottomConstraint.isActive = true

以编程方式更新约束？

2 个答案: