对子视图控制器使用自动布局

Question

我再次遇到自动布局问题...

这是我最后想要得到的：

我正在使用父视图控制器和子视图控制器顶部，中央和底部执行代码中的所有操作。

最后，我希望能够将顶视图控制器的高度设置为其固有高度–这就是我现在要失败的地方...顶视图控制器具有用于放置元素的垂直堆栈视图（以便最终能够根据需要添加和删除视图）。

此实现...

import UIKit

class ParentViewController: UIViewController {

    lazy var topChildView: UIView = {
        let topView = topChildViewController.view!
        topView.backgroundColor = .red
        topView.translatesAutoresizingMaskIntoConstraints = false
        topView.accessibilityIdentifier = "top"
        return topView
    }()

    lazy var topChildViewController: TopChildViewController = {
        let topVC = TopChildViewController()
        return topVC
    }()

    lazy var centerChildView: UIView = {
        let centerView = centerChildViewController.view!
        centerView.backgroundColor = .blue
        centerView.translatesAutoresizingMaskIntoConstraints = false
        centerView.accessibilityIdentifier = "center"
        return centerView
    }()

    lazy var centerChildViewController: CenterChildViewController = {
        let centerVC = CenterChildViewController()
        return centerVC
    }()

    lazy var bottomChildView: UIView = {
        let bottomView = bottomChildViewController.view!
        bottomView.backgroundColor = .green
        bottomView.translatesAutoresizingMaskIntoConstraints = false
        bottomView.accessibilityIdentifier = "bottom"
        return bottomView
    }()

    lazy var bottomChildViewController: BottomChildViewController = {
        let bottom = BottomChildViewController()
        return bottom
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .gray

        self.addChild(topChildViewController)
        self.view.addSubview(topChildView)

        self.addChild(centerChildViewController)
        self.view.addSubview(centerChildView)

        self.addChild(bottomChildViewController)
        self.view.addSubview(bottomChildView)

        NSLayoutConstraint.activate([
            topChildView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 12),
            topChildView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor, constant: 12),
            topChildView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: -12),
            topChildView.heightAnchor.constraint(equalToConstant: topChildView.intrinsicContentSize.height),

            centerChildView.topAnchor.constraint(equalTo: topChildView.bottomAnchor),
            centerChildView.leadingAnchor.constraint(equalTo: topChildView.leadingAnchor),
            centerChildView.trailingAnchor.constraint(equalTo: topChildView.trailingAnchor),

            bottomChildView.leadingAnchor.constraint(equalTo: topChildView.leadingAnchor),
            bottomChildView.trailingAnchor.constraint(equalTo: topChildView.trailingAnchor),
            bottomChildView.heightAnchor.constraint(equalToConstant: 100),
            bottomChildView.topAnchor.constraint(equalTo: centerChildView.bottomAnchor),
            bottomChildView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -12),
        ])
    }

}

class TopChildViewController: UIViewController {

    lazy var stackView: UIStackView = {
        let s = UIStackView()
        s.translatesAutoresizingMaskIntoConstraints = false
        s.axis = .vertical
        s.distribution = .fillEqually
        s.spacing = 6
        return s
    }()

    lazy var textField: UITextField = {
        let t = UITextField()
        t.borderStyle = .roundedRect
        t.placeholder = "Some fancy text"
        t.accessibilityIdentifier = "textfield"
        t.translatesAutoresizingMaskIntoConstraints = false
        return t
    }()

    lazy var label: UILabel = {
        let l = UILabel()
        l.accessibilityIdentifier = "label"
        l.translatesAutoresizingMaskIntoConstraints = false
        l.text = "Awesome Label"
        l.textAlignment = .center
        return l
    }()

    override func loadView() {
        view = UIView()

        view.addSubview(stackView)

        stackView.addArrangedSubview(textField)
        stackView.addArrangedSubview(label)

        NSLayoutConstraint.activate([


            textField.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 12),
            textField.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor, constant: 12),
            textField.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: -12),

            label.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            label.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -12)
        ])
    }
}

class CenterChildViewController: UIViewController {
    override func loadView() {
        view = UIView()
    }
}

class BottomChildViewController: UIViewController {
    override func loadView() {
        view = UIView()
    }
}

...导致此结果：

虽然我知道该错误（在尝试访问它时，固有高度似乎不可用，请参阅下文，但我不知道如何解决-我缺少什么？

是否需要在其他地方创建约束？我真的很希望能够从父视图控制器对其进行控制...

[LayoutConstraints] Unable to simultaneously satisfy constraints.
  Probably at least one of the constraints in the following list is one
you don't want.   Try this:       (1) look at each constraint and try to
figure out which you don't expect;        (2) find the code that added the
unwanted constraint or constraints and fix it.  (
    "<NSLayoutConstraint:0x600002306d50 top.height == - 1   (active, names: top:0x7f81c1e1f120 )>" )

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x600002306d50 top.height == - 1   (active, names:
top:0x7f81c1e1f120 )>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints
to catch this in the debugger. The methods in the
UIConstraintBasedLayoutDebugging category on UIView listed in
<UIKitCore/UIView.h> may also be helpful.

Answer 1

因此，我在ParentViewController.viewDidLoad()中提供的约束如下：

NSLayoutConstraint.activate([
            topChildView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 12),
            topChildView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor, constant: 12),
            topChildView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor, constant: -12),

            centerChildView.topAnchor.constraint(equalTo: topChildView.bottomAnchor),
            centerChildView.leadingAnchor.constraint(equalTo: topChildView.leadingAnchor),
            centerChildView.trailingAnchor.constraint(equalTo: topChildView.trailingAnchor),

            bottomChildView.leadingAnchor.constraint(equalTo: topChildView.leadingAnchor),
            bottomChildView.trailingAnchor.constraint(equalTo: topChildView.trailingAnchor),
            bottomChildView.heightAnchor.constraint(equalToConstant: 100),
            bottomChildView.topAnchor.constraint(equalTo: centerChildView.bottomAnchor),
            bottomChildView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: -12),
        ])