约束计数在AutoLayout中始终为零(0)-iOS [英] Constrains count is always getting zero ( 0 ) in AutoLayout - iOS

问题描述

我遇到一个奇怪的问题，我正在使用情节提要在视图上设置约束，如下所示:

I am getting one weird issue, I am setting constraints on the view using storyboard as below:

但是，如果我通过代码访问所有应用的约束，那么总会得到零(0).

But if I am accessing all applied constraint by code then always getting zero (0).

对于self.view，它返回约束，但对于黄色视图，它返回零.

for self.view it's returning the constraint but for yellow view getting zero.

推荐答案

使用此代码(Swift 4+和Xcode 9.4.1)

import UIKit

class ViewController: UIViewController {

@IBOutlet var subView: UIView!

override func viewDidLoad() {
    super.viewDidLoad()
    print(self.view.getAllConstraints().count)
    print(self.subView.getAllConstraints().count)
  }
}

extension UIView {

func getAllConstraints() -> [NSLayoutConstraint] {
    var views = [self]
    var view = self
    while let superview = view.superview {
        views.append(superview)
        view = superview
    }
    return views.flatMap({ $0.constraints }).filter { constraint in
        return constraint.firstItem as? UIView == self ||
            constraint.secondItem as? UIView == self
    }
   }
  }

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