XCode：以编程方式获取特定约束

Question

我以编程方式将childVC（DrawerViewController）内置到mainVC（HomeController）中，现在我需要topAnchor参考。

我知道我可以使用IBOutlets引用单个约束并将其命名，但是我想学习如何以编程方式构建没有Storyboard的东西。现在，我很难解决如何以编程方式正确引用我的子容器的topAnchor来进一步处理此变量的问题。

作为IBO，它会像这样完美地工作：

@IBOutlet private var containerViewTopConstraint: NSLayoutConstraint!

因此，我需要以编程方式引用我的topAnchor，并将其命名为containerViewTopConstraint。以编程方式嵌入childVC的代码：

let drawerViewController = DrawerViewController()

func addDrawer() {
    addChild(drawerViewController)
    view.addSubview(drawerViewController.view)
    drawerViewController.didMove(toParent: self)
    addDrawerConstraints()
}

func addDrawerConstraints() {
    drawerViewController.view.translatesAutoresizingMaskIntoConstraints = false
    drawerViewController.view.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 20).isActive = true
    drawerViewController.view.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0).isActive = true
    drawerViewController.view.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0).isActive = true
    drawerViewController.view.heightAnchor.constraint(equalToConstant: UIScreen.main.bounds.height).isActive = true
}

override func viewDidLoad() {
    super.viewDidLoad()

    addDrawer()
}

Answer 1

这是我的操作方式。它涉及两件事。首先，设置always相同的约束，设置为isActive = true。然后，对于一个（或多个），根据需要激活/停用：

let drawer = UIView()
var drawerOut = [NSLayoutConstraint]()
var drawerIn = [NSLayoutConstraint]()

// place in viewDidLoad()

drawer.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
drawer.widthAnchor.constraint(equalToConstant: 526).isActive = true
drawer.heightAnchor.constraint(equalToConstant: 374).isActive = true

drawerIn.append(drawer.topAnchor.constraint(equalTo: view.bottomAnchor, constant: 526))
drawerOut.append(drawer.topAnchor.constraint(equalTo: safeAreaView.bottomAnchor, constant: -370))
NSLayoutConstraint.activate(drawerIn)

// functions to open/close drawer

func openDrawer() {
    NSLayoutConstraint.deactivate(drawerIn)
    NSLayoutConstraint.activate(drawerOut)
    UIView.animate(withDuration: 0.3) { self.view.layoutIfNeeded() }
}

func closeDrawer() {
    NSLayoutConstraint.deactivate(drawerOut)
    NSLayoutConstraint.activate(drawerIn)
    UIView.animate(withDuration: 0.3) { self.view.layoutIfNeeded() }
}

UIView.animate(withDuration:)为所有内容添加了漂亮的动画。