如何根据用户输入更新约束

Question

我有一个视图控制器视图，默认情况下有3个列部分（称为leg，aView，bView和cView）。用户可以在设置菜单中将其在2和3之间切换，该菜单在同一屏幕上以模态方式呈现。

我试图让列在屏幕上平均占用空间，所以当有3列时，它们各自占据宽度的大约1/3（忽略填充），当有2列时，它们各自占用大约1/2。

我当前的方法是设置一些始终处于活动状态的约束，然后使用if语句设置根据列数更改的约束。我尝试了一些layoutIfNeeded()，removeConstraints和其他变种，但不完全确定如何实现它们。

有关代码的一些说明，xView是列视图，其中包含xTitle和xTextView。文本视图上方还有一个mainButton，文本视图下方还有button1。这一切都存在于contentView和scrollView设置中。

let sidePadding: CGFloat = 15


func placeViews() { // run in viewWillAppear

        let alwaysConstraints = [
            aView.topAnchor.constraint(equalTo: mainButton.bottomAnchor, constant: 25),
            aView.leftAnchor.constraint(equalTo: contentView.leftAnchor, constant: sidePadding),
            aView.rightAnchor.constraint(equalTo: bView.leftAnchor),
            bView.topAnchor.constraint(equalTo: aView.topAnchor),
            bView.bottomAnchor.constraint(equalTo: aView.bottomAnchor),
            aTitle.topAnchor.constraint(equalTo: aView.topAnchor),
            bTitle.topAnchor.constraint(equalTo: aTitle.topAnchor),
            aTitle.centerXAnchor.constraint(equalTo: aView.centerXAnchor),
            bTitle.centerXAnchor.constraint(equalTo: bView.centerXAnchor),
            aTextView.topAnchor.constraint(equalTo: aTitle.bottomAnchor, constant: 25),
            bTextView.topAnchor.constraint(equalTo: aTextView.topAnchor),
            aTextView.bottomAnchor.constraint(equalTo: aView.bottomAnchor),
            bTextView.bottomAnchor.constraint(equalTo: aTextView.bottomAnchor),
            aTextView.centerXAnchor.constraint(equalTo: aView.centerXAnchor),
            bTextView.centerXAnchor.constraint(equalTo: bView.centerXAnchor),
            aTextView.widthAnchor.constraint(equalTo: aView.widthAnchor),
            bTextView.widthAnchor.constraint(equalTo: bView.widthAnchor),
            bView.widthAnchor.constraint(equalTo: aView.widthAnchor),

            // Restrict buttons to leg views
            button1.heightAnchor.constraint(equalToConstant: buttonHeight),
            button1.leftAnchor.constraint(equalTo: contentView.leftAnchor, constant: 20),
            button1.rightAnchor.constraint(equalTo: contentView.rightAnchor, constant: -20),
            button1.topAnchor.constraint(equalTo: aView.bottomAnchor, constant: 40),

            // Restrict button to bottom
            button1.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -20)
        ]




        let twoLegConstraints = [
            aView.widthAnchor.constraint(equalToConstant: (view.frame.width - (sidePadding * 2) / 2)),
            bView.rightAnchor.constraint(equalTo: contentView.rightAnchor, constant: -sidePadding),
        ]

        let threeLegConstraints = [
            aView.widthAnchor.constraint(equalToConstant: (view.frame.width - (sidePadding * 2)) / 3),
            bView.rightAnchor.constraint(equalTo: cView.leftAnchor),
            cView.rightAnchor.constraint(equalTo: contentView.rightAnchor, constant: -sidePadding),
            cView.topAnchor.constraint(equalTo: aView.topAnchor),
            cView.bottomAnchor.constraint(equalTo: aView.bottomAnchor),
            cTitle.topAnchor.constraint(equalTo: aTitle.topAnchor),
            cTitle.centerXAnchor.constraint(equalTo: cView.centerXAnchor),
            cTextView.topAnchor.constraint(equalTo: aTextView.topAnchor),
            cTextView.bottomAnchor.constraint(equalTo: aTextView.bottomAnchor),
            cTextView.centerXAnchor.constraint(equalTo: cView.centerXAnchor),
            cTextView.widthAnchor.constraint(equalTo: cView.widthAnchor),
            cView.widthAnchor.constraint(equalTo: aView.widthAnchor),
        ]





        NSLayoutConstraint.activate(alwaysConstraints)

        if legs == 2 {
            cView.isHidden = true
            NSLayoutConstraint.activate(twoLegConstraints)
        } else if legs == 3 {
            cView.isHidden = false
            NSLayoutConstraint.activate(threeLegConstraints)
        }
    }

此时，屏幕默认以3开始，并且完美运行（每个~1 / 3屏幕宽度）。然后用户可以将其切换为2，并且它再次完美地工作（每个~1 / 2屏幕宽度）。然后切换回3，前两个根本不变，第三列出现在屏幕的右边缘。

Answer 1

使用distribution = .fillEqually的堆栈视图。当您设置任何视图的isHidden属性时，它将自动处理布局和约束。