在 iPad 上使用 Slide Over 时多行 UILabel 截断为 1 行

Question

我有一个UITableView 的tableHeaderView 属性，其中包含一个UIImage、一个单行UILabel，然后是一个多行UILabel。约束设置如下：

self.addConstraints([
    // App icon constraints
    NSLayoutConstraint(item: self.image, attribute: .Top, relatedBy: .Equal, toItem: self, attribute: .Top, multiplier: 1, constant: 8),
    NSLayoutConstraint(item: self.image, attribute: .CenterX, relatedBy: .Equal, toItem: self, attribute: .CenterX, multiplier: 1, constant: 0),
    NSLayoutConstraint(item: self.image, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 128),
    NSLayoutConstraint(item: self.image, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 128),

    // App name label constraints
    NSLayoutConstraint(item: self.appNameLabel, attribute: .Top, relatedBy: .Equal, toItem: self.image, attribute: .Bottom, multiplier: 1, constant: 8),
    NSLayoutConstraint(item: self.appNameLabel, attribute: .Leading, relatedBy: .Equal, toItem: self, attribute: .Leading, multiplier: 1, constant: 16),
    NSLayoutConstraint(item: self.appNameLabel, attribute: .Trailing, relatedBy: .Equal, toItem: self, attribute: .Trailing, multiplier: 1, constant: -16),

    // Description label constrains
    NSLayoutConstraint(item: self.descriptionLabel, attribute: .Top, relatedBy: .Equal, toItem: self.appNameLabel, attribute: .Bottom, multiplier: 1, constant: 8),
    NSLayoutConstraint(item: self.descriptionLabel, attribute: .Leading, relatedBy: .Equal, toItem: self, attribute: .Leading, multiplier: 1, constant: 16),
    NSLayoutConstraint(item: self.descriptionLabel, attribute: .Trailing, relatedBy: .Equal, toItem: self, attribute: .Trailing, multiplier: 1, constant: -16),
    NSLayoutConstraint(item: self.descriptionLabel, attribute: .Bottom, relatedBy: .Equal, toItem: self, attribute: .Bottom, multiplier: 1, constant: -8)
    ])

这会产生以下内容：

由于以下代码，我可以旋转设备，标签将调整为正确的大小：

override func layoutSubviews() {
    self.updateDescriptionLabelPMLW()

    super.layoutSubviews()
}

private func updateDescriptionLabelPMLW() {
    // -32 for the 16 padding on the left and right
    let newValue = self.frame.width - 32

    if self.descriptionLabel.preferredMaxLayoutWidth != newValue {
        self.descriptionLabel.preferredMaxLayoutWidth = newValue
        self.descriptionLabel.sizeToFit()
    }
}

尽管这在 iOS 7.0-9.0 上工作（这只是一个奇迹），但当我使用 Slide Over -> Split View feature of the iPad Air 2（模拟器）时，当在“拆分”应用，如以下屏幕截图所示：

请注意，这只发生在横向，并且可以通过旋转设备来“修复”。

Answer 1

通过将updateDescriptionLabelPMLW 方法更新为：

private func updateDescriptionLabelPMLW() {
    /*
    iOS 7
    Tested on:
    - iPad 2 (7.0.6)
    - iPhone 4 (7.1.1)

    iOS 8.1
    Tested on:
    - iPhone 5 (sim)
    - iPad Retina (sim)

    iOS 9
    Tested on:
    - iPhone 6
    - iPad Air 2

    Does not work on iPad Air 2 when sliding in an app (label is truncated)
    */
    // -32 for the 16 padding on the left and right
    let newValue = self.frame.width - 32

    if self.descriptionLabel.preferredMaxLayoutWidth != newValue {
        self.descriptionLabel.preferredMaxLayoutWidth = newValue
        self.descriptionLabel.sizeToFit()

        // Check for iOS 9 devices in landscape
        // This should also check for iPads (specifically iPad Air 2)
        if #available(iOS 9.0, *) {
            if UIInterfaceOrientationIsLandscape(UIApplication.sharedApplication().statusBarOrientation) {
                self.superview?.setNeedsLayout()
                self.superview?.layoutIfNeeded()
            }
        }
    }
}

它可能并不完美，但它已经修复了错误！