假设我有一个 UIView，

 class CleverView: UIView

在自定义类中，我想这样做:

func changeWidth() {

  let c = ... find my own layout constraint, for "width"
  c.constant = 70 * Gameinfo.ImportanceOfEnemyFactor
}

同样，我希望能够像那样“找到”约束(或者我猜，所有约束，可能不止一个)附加到四个边之一。

因此，查看所有附加到我的约束，并找到任何宽度/高度的约束，或者实际上与给定(例如，“左”)边缘相关的任何约束。

有什么想法吗？

也许值得注意this question

请注意，(显然)我在问如何以动态/编程方式执行此操作。

(是的，您可以说“链接到约束”或“使用 ID”——QA 的重点是如何即时找到它们并动态工作。)

如果您不熟悉约束，请注意 .constraints 只是为您提供存储在“那里”的末端。

最佳答案

实际上有两种情况:

1. 有关 View 大小或与 subview 的关系的约束保存在自身中
2. 两个 View 之间的约束保存在 View 的最低共同祖先中

重复。对于两个 View 之间的约束。事实上，iOS 总是将它们存储在最低的公共(public)祖先中。因此，始终可以通过搜索 View 的所有祖先来找到 View 的约束。

因此，我们需要检查 View 本身及其所有父 View 的约束。一种方法可能是:

extension UIView {

    // retrieves all constraints that mention the view
    func getAllConstraints() -> [NSLayoutConstraint] {

        // array will contain self and all superviews
        var views = [self]

        // get all superviews
        var view = self
        while let superview = view.superview {
            views.append(superview)
            view = superview
        }

        // transform views to constraints and filter only those
        // constraints that include the view itself
        return views.flatMap({ $0.constraints }).filter { constraint in
            return constraint.firstItem as? UIView == self ||
                constraint.secondItem as? UIView == self
        }
    }
}

在获得有关 View 的所有约束后，您可以应用各种过滤器，我想这是最困难的部分。一些例子:

extension UIView {

    // Example 1: Get all width constraints involving this view
    // We could have multiple constraints involving width, e.g.:
    // - two different width constraints with the exact same value
    // - this view's width equal to another view's width
    // - another view's height equal to this view's width (this view mentioned 2nd)
    func getWidthConstraints() -> [NSLayoutConstraint] {
        return getAllConstraints().filter( {
            ($0.firstAttribute == .width && $0.firstItem as? UIView == self) ||
            ($0.secondAttribute == .width && $0.secondItem as? UIView == self)
        } )
    }

    // Example 2: Change width constraint(s) of this view to a specific value
    // Make sure that we are looking at an equality constraint (not inequality)
    // and that the constraint is not against another view
    func changeWidth(to value: CGFloat) {

        getAllConstraints().filter( {
            $0.firstAttribute == .width &&
                $0.relation == .equal &&
                $0.secondAttribute == .notAnAttribute
        } ).forEach( {$0.constant = value })
    }

    // Example 3: Change leading constraints only where this view is
    // mentioned first. We could also filter leadingMargin, left, or leftMargin
    func changeLeading(to value: CGFloat) {
        getAllConstraints().filter( {
            $0.firstAttribute == .leading &&
                $0.firstItem as? UIView == self
        }).forEach({$0.constant = value})
    }
}

//编辑:增强示例并在注释中阐明它们的解释

关于ios - "find"如何约束自己？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47053727/