仅限 iOS 11 : Navigation bar label off on top

Question

IOS 11 导致主标签从顶部移动一点点，而不是保持在顶部。该问题仅出现在 IOS 11 上。对于不同的 IOS，一切看起来都正常。

带有设置标题的代码示例:

    private func setHeader(agentName: String = "", isTyping: Bool = false) -> Void {
    if (agentName.isEmpty) {
        self.containerViewController?.navigationItem.titleView = nil
    } else {
        let headerView: UIView = {
            let rect = CGRect(x: 0, y: 0, width: 320, height: 44)
            let uiview = UIView(frame: rect)

            return uiview
        }()


        let headerLabel: UILabel = {
            let label = UILabel(frame: CGRect(x: 0, y: 0, width: headerView.frame.width, height: 20))
            label.font = UIFont.systemFont(ofSize: 18)
            label.textAlignment = .center
            label.translatesAutoresizingMaskIntoConstraints = false
            return label
        }()

        let subheaderLabel: UILabel = {
            let label = UILabel(frame: CGRect(x: 0, y: 0, width: headerView.frame.width, height: 12))
            label.font = UIFont.systemFont(ofSize: 12)
            label.translatesAutoresizingMaskIntoConstraints = false
            label.text = self.title
            return label
        }()


        headerView.addSubview(headerLabel)
        headerView.addSubview(subheaderLabel)

        let viewsDictionary = ["header": headerLabel, "subheader": subheaderLabel]
        headerView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[header]|", options: NSLayoutFormatOptions(), metrics: nil, views: viewsDictionary))
        headerView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[subheader]|", options: NSLayoutFormatOptions(), metrics: nil, views: viewsDictionary))
        headerView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[header(20)]-[subheader]", options: [], metrics: nil, views: viewsDictionary))

        self.containerViewController?.navigationItem.titleView = headerView

    }
}

Answer 1

从 iOS 11 开始，添加到工具栏的 View 现在使用自动布局进行布局。您应该在 headerView 上添加大小限制。例如:

headerView.widthAnchor.constraintEqualToConstant(320.0).isActive = true
headerView.heightAnchor.constraintEqualToConstant(44.0).isActive = true

否则，自动布局将使用标题 View 的固有内容大小，这可能不是您所期望的。

有关更多信息，请参阅 WWDC 2017 session Updating your app for iOS 11 .