iOS9：UIScrollView又坏了？

Question

我注意到 UIScrollView 可能又坏了。我正在使用 OS X 10.11.1 和 Xcode 7 (from AppStore) 或 Xcode 7.1 beta。 AutoLayout 完成工作后，contentOffset 属性不在 UIScrollView 的 origin 处。

有人可以确认这个问题吗？

然而，我设法解决了这个问题，但这并不是它应该的样子：

override func viewDidLayoutSubviews() {

    super.viewDidLayoutSubviews()

    self.scrollView.contentOffset = CGPoint(x: 0, y: -self.scrollView.frame.origin.y)
    /* if you need a different position, I suggest to safe the 
       contentOffset inside viewWillLayoutSubviews and calculate the offset here */
}

重现问题的方法如下：

import UIKit

class ViewController: UIViewController, UIScrollViewDelegate {

    private let scrollView = UIScrollView()
    private let containerView = UIView()

    override func loadView() {

        self.view = UIView()
        self.view.backgroundColor = UIColor.whiteColor()
    }

    override func viewDidLoad() {

        super.viewDidLoad()

        self.scrollView.layer.borderColor = UIColor.greenColor().CGColor
        self.scrollView.layer.borderWidth = 1.0
        self.scrollView.clipsToBounds = false

        self.scrollView.translatesAutoresizingMaskIntoConstraints = false

        self.view.addSubview(scrollView)

        self.scrollView.topAnchor.constraintEqualToAnchor(self.topLayoutGuide.bottomAnchor).active = true
        self.scrollView.heightAnchor.constraintEqualToAnchor(self.view.widthAnchor).active = true
        self.scrollView.widthAnchor.constraintEqualToAnchor(self.view.widthAnchor).active = true

        self.containerView.backgroundColor = UIColor.redColor()
        self.containerView.translatesAutoresizingMaskIntoConstraints = false

        self.scrollView.addSubview(self.containerView)

        self.containerView.widthAnchor.constraintEqualToAnchor(self.scrollView.widthAnchor).active = true
        self.containerView.heightAnchor.constraintEqualToAnchor(self.scrollView.heightAnchor).active = true
    }

    override func viewDidLayoutSubviews() {

        super.viewDidLayoutSubviews()

        print("content offset: \(self.scrollView.contentOffset)")
        print("origin: \(self.scrollView.frame.origin)")
        print("they to not match visually :( <-- BROKEN !!!")
    }

    override func supportedInterfaceOrientations() -> UIInterfaceOrientationMask {

        return UIInterfaceOrientationMask.Portrait
    }

    override func prefersStatusBarHidden() -> Bool {

        return false
    }
}

更新： 已报告并填充了雷达：22770934

更新 2：问题已解决。

Answer 1

我在视图调试器的帮助下找到了解决方案。

添加这个缺失的约束，一切都会好起来的：

self.containerView.topAnchor.constraintEqualToAnchor(self.scrollView.topAnchor).active = true
self.containerView.leftAnchor.constraintEqualToAnchor(self.scrollView.leftAnchor).active = true
self.containerView.rightAnchor.constraintEqualToAnchor(self.scrollView.rightAnchor).active = true
self.containerView.bottomAnchor.constraintEqualToAnchor(self.scrollView.bottomAnchor).active = true

// actually the debugger showed two different constraints, but this had no effect on the functionality, correct me here if I am wrong
// trailing and button constraints where like this:

// self.scrollView.trailingAnchor.constraintEqualToAnchor(self.containerView.trailingAnchor).active = true
// self.scrollView.bottomAnchor.constraintEqualToAnchor(self.containerView.bottomAnchor).active = true

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