ios - 由于未捕获的异常 'NSGenericException' 而终止应用程序，原因 : 'Unable to activate constraint with anchors

Question

我正在尝试寻找并思考这个问题，但我找不到解决它的最佳解决方案!我不明白这是什么意思？!

Terminating app due to uncaught exception 'NSGenericException', reason: 'Unable to activate constraint with anchors and because they have no common ancestor. Does the constraint or its anchors reference items in different view hierarchies? That's illegal.'

代码:

private let logoImageView: UIImageView = {
    let imgView = UIImageView()
    imgView.image = UIImage(named: "LogoBlue")
    return imgView
}()

func setupLogo() {

    if #available(iOS 11.0, *) {
        view.add(subview: logoImageView) { (v, p) in [
            v.topAnchor.constraint(equalTo: p.safeAreaLayoutGuide.topAnchor, constant: 50),
            v.centerXAnchor.constraint(equalTo: p.centerXAnchor),
            v.heightAnchor.constraint(equalTo: p.widthAnchor, multiplier: 0.5),
            v.widthAnchor.constraint(equalTo: p.widthAnchor, multiplier: 0.5)
        ]}
    } else {
        view.add(subview: logoImageView) { (v, p) in [
            v.topAnchor.constraint(equalTo: p.topAnchor, constant: 50),
            v.centerXAnchor.constraint(equalTo: p.centerXAnchor),
            v.heightAnchor.constraint(equalTo: p.widthAnchor, multiplier: 0.5),
            v.widthAnchor.constraint(equalTo: p.widthAnchor, multiplier: 0.5)
        ]}
    }
}

扩展名:

extension UIView {
    func add(subview: UIView, createConstraints: (_ view: UIView, _ parebt: UIView) -> [NSLayoutConstraint]) {
        subview.activate(constraints: createConstraints(subview, self))
    }

    func activate(constraints: [NSLayoutConstraint]) {
        translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate(constraints)
    }
}

Answer 1

您需要添加UIView在应用约束之前在层次结构上。

换句话说，您需要<#PARENT_HERE#>.addSubview(<#CHILD_HERE#>)

您可以将扩展名更改为:

extension UIView {
    func add(subview: UIView, createConstraints: (_ view: UIView, _ parebt: UIView) -> [NSLayoutConstraint]) {
        self.addSubview(subview) // <
        subview.activate(constraints: createConstraints(subview, self))
    }

    func activate(constraints: [NSLayoutConstraint]) {
        translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate(constraints)
    }
}

如果您可以修改您的扩展程序，这绝对是我的解决方案。

---

另一个不太花哨的解决方案是在扩展程序之外手动添加每个 subview :

func setupLogo() {
    self.view.addSubview(logoImageView) // assuming self.view is not nil
    if #available(iOS 11.0, *) {
        view.add(subview: logoImageView) { (v, p) in [
            v.topAnchor.constraint(equalTo: p.safeAreaLayoutGuide.topAnchor, constant: 50),
            v.centerXAnchor.constraint(equalTo: p.centerXAnchor),
            v.heightAnchor.constraint(equalTo: p.widthAnchor, multiplier: 0.5),
            v.widthAnchor.constraint(equalTo: p.widthAnchor, multiplier: 0.5)
        ]}
    } else {
        view.add(subview: logoImageView) { (v, p) in [
            v.topAnchor.constraint(equalTo: p.topAnchor, constant: 50),
            v.centerXAnchor.constraint(equalTo: p.centerXAnchor),
            v.heightAnchor.constraint(equalTo: p.widthAnchor, multiplier: 0.5),
            v.widthAnchor.constraint(equalTo: p.widthAnchor, multiplier: 0.5)
        ]}
    }
}

注意:这是辅助解决方案，请勿同时使用两者。