以下是2018年10月23日更新
经过大约一个月的时间的适配，项目正式使用XCode10(以下简称为10 or XC10)大部分库都升级为Swift4.2（以下简称为 4.2 or S4.2），下面是适配过程中遇到的一些坑。
1. Swift4、Swift4.2混编
如果你对项目是小的独立项目，完全可以全部升级为4.2，你可以略过第一条；如果你依赖了一些第三方的库，且没有升级4.2，你可以继续看这一条。目前测试的结果来看，Swift4 和 S4.2的混编没有什么大的问题，如果你是通过cocoapod引入的可以在Podfile中加入如下代码：
swift_41_pod_targets = ['your_target_name']post_install do |installer| installer.pods_project.targets.each do |target| if swift_41_pod_targets.include?(target.name) target.build_configurations.each do |config| config.build_settings['SWIFT_VERSION'] = '4.1' end end endend复制代码
2. NSDataAsset
升级XC10和S.2之前，项目里面有些对 'NSDataAsset' 的错误使用： 用‘NSDataAsset’读ImageAsset中的图片，这个是不正确的，但是却可以工作，这次升级修复了这个BUG。
正确的做法使用'DataAsset'，然后才可以用‘NSDataAsset’读取数据，我由于不够认真且经验不足还以为是个BUG，给Apple提了个BUG。。。[捂脸]
3. 第三方库的重命名 typealias
为了方便的适配S4.2对UIKit中的重命名，有些第三方使用typealias对一些类型进行了重命名，以 RxSwift 为例子，RxSwift中就有如下代码：
#if swift(>=4.2) public typealias UIControlEvents = UIControl.Event private#endif复制代码
这会导致一些重命名的类型即使不改也不会报错，但是一旦去掉了对某个库的依赖就会引入新的问题。
4.Delegate 的 Access Modifier
在升级S4.2过程中，XC偶尔会提示需要给某些Delegate方法添加 private修饰符，不要为了消除这个⚠️添加private，可能会导致Delegate永远不被调到；另外，如果是一个public或者open的class，协议方法记得也要加上public，否则会出一样的问题，具体原因我还在测试，但是现象是这样的，有新的见解欢迎评论区讨论。
5. 机型适配问题，iPhone XS Max字体变大
有些同事遇到XC9构建的安装包在iPhone XS Max上会有字体变大的情况，这个貌似是普遍现象，微信也有，使用XC10构建安装包可以解决这个问题，但是会遇到问题6
###6. iOS9.3以下系统Crash率飙升 使用XC10构建安装包可以解决问题5，但是iOS9.3以下的系统Crash到让你怀疑人生
以下是2018年9月18日内容
AVAudioSession.sharedInstance().setCategory()
disappeared
Swift 4.2 中 iOS10以下不能用 AVAudioSession.sharedInstance() setCategory
可选方案:
- 使用OC实现该部分，然后使用Swift调用
- 放弃 iOS9用户体验
do { if #available(iOS 11.0, *) { try audioSession.setCategory(.playback, mode: .default, policy: .longForm, options: []) } else if #available(iOS 10.0, *) { try audioSession.setCategory(.playback, mode: .default, options: []) } else { // Compiler error: 'setCategory' is unavailable in Swift try audioSession.setCategory(AVAudioSession.Category.playback) }} catch let error { print("Unable to configure audio sesson category: \(error)")}复制代码 NSUnderlineStyle(.patternSolid、.none)
disappeared
可选方案:
Wrong: mutableAttributedString.addAttribute(NSAttributedString.Key.underlineStyle, value: [], range: range) Right: mutableAttributedString.addAttribute(NSAttributedString.Key.underlineStyle, value: 0, range: range)
下面是Rename操作
UIKit
#Swift4/UIKit
UITableViewCell
| Swift 4 | Swift 4.2 |
| UITableViewCellStyle | UITableViewCell.CellStyle |
UIEvent
| Swift 4 | Swift 4.2 |
| UIEventSubtype | UIEvent.EventSubtype |
UITableView
| Swift 4 | Swift 4.2 |
| UITableViewScrollPosition | UITableView.ScrollPosition |
| UITableViewAutomaticDimension | UITableView.automaticDimension |
| UITableViewCellEditingStyle | UITableViewCell.EditingStyle |
| UITableViewRowAnimation | UITableView.RowAnimation |
| UITableViewStyle | UITableView.Style |
| UITableViewCellAccessoryType | UITableViewCell.AccessoryType |
UIControl
| Swift 4 | Swift 4.2 |
| UIControlEvents | UIControl.Event |
UIWindow
| Swift 4 | Swift 4.2 |
| UIWindowLevelAlert | UIWindow.Level.alert |
| UIKeyboardFrameEndUserInfoKey | UIResponder.keyboardFrameEndUserInfoKey |
| UIKeyboardFrameBeginUserInfoKey | UIResponder.keyboardFrameBeginUserInfoKey |
| UIKeyboardAnimationDurationUserInfoKey | UIResponder.keyboardAnimationDurationUserInfoKey |
| UIKeyboardAnimationCurveUserInfoKey | UIResponder.keyboardAnimationCurveUserInfoKey |
| UIKeyboardIsLocalUserInfoKey | UIResponder.keyboardIsLocalUserInfoKey |
| UIWindowDidBecomeVisible | UIWindow.didBecomeVisibleNotification |
| UIWindowDidBecomeHidden | UIWindow.didBecomeHiddenNotification |
| UIWindowDidBecomeKey | UIWindow.didBecomeKeyNotification |
| UIWindowDidResignKey | UIWindow.didResignKeyNotification |
| UIKeyboardWillShow | UIResponder.keyboardWillShowNotification |
| UIKeyboardDidShow | UIResponder.keyboardDidShowNotification |
| UIKeyboardWillHide | UIResponder.keyboardWillHideNotification |
| UIKeyboardDidHide | UIResponder.keyboardDidHideNotification |
UIViewController
| Swift 4 | Swift 4.2 |
| open func addChildViewController(_ childController: UIViewController) | open func addChild(_ childController: UIViewController) |
| open func willMove(toParentViewController parent: UIViewController?) | open func willMove(toParent parent: UIViewController?) |
| open func didMove(toParentViewController parent: UIViewController?) | open func didMove(toParent parent: UIViewController?) |
| open func removeFromParentViewController() | open func removeFromParent() |
UIActivity
| Swift 4 | Swift 4.2 |
| UIActivityType | UIActivity.ActivityType |
UIActivityIndicatorView
| Swift 4 | Swift 4.2 |
| activityIndicator.activityIndicatorViewStyle | activityIndicator.style |
UIAlertController
| Swift 4 | Swift 4.2 |
| UIAlertActionStyle | UIAlertAction.Style |
| UIAlertControllerStyle | UIAlertController.Style |
UIPageViewController
| Swift 4 | Swift 4.2 |
| UIPageViewControllerNavigationDirection | UIPageViewController.NavigationDirection |
| UIPageViewControllerSpineLocation | UIPageViewController.SpineLocation |
| UIPageViewControllerNavigationOrientation | UIPageViewController.NavigationOrientation |
| UIPageViewControllerTransitionStyle | UIPageViewController.TransitionStyle |
| UIPageViewControllerOptionsKey | UIPageViewController.OptionsKey |
UINavigationController
| Swift 4 | Swift 4.2 |
| UINavigationControllerOperation | UINavigationController.Operation |
UIGestureRecognizer
| Swift 4 | Swift 4.2 |
| UIGestureRecognizerStatePossible | UIGestureRecognizer.State.possible |
| UIGestureRecognizerStateBegan | UIGestureRecognizer.State.began |
| UIGestureRecognizerStateChanged | UIGestureRecognizer.State.changed |
| UIGestureRecognizerStateEnded | UIGestureRecognizer.State.ended |
| UIGestureRecognizerStateCancelled | UIGestureRecognizer.State.cancelled |
| UIGestureRecognizerStateFailed | UIGestureRecognizer.State.failed |
| UIGestureRecognizerStateRecognized | UIGestureRecognizer.State.recognized |
NSLayoutFormat
| Swift 4 | Swift 4.2 |
| NSLayoutFormatOptions | NSLayoutConstraint.FormatOptions |
UIEdgeInsets
| Swift 4 | Swift 4.2 |
| public func UIEdgeInsetsMake(_ top: CGFloat, _ left: CGFloat, _ bottom: CGFloat, _ right: CGFloat) -> UIEdgeInsets | UIEdgeInsets(top: CGFloat, left: CGFloat, bottom: CGFloat, right: CGFloat) |
| public func UIEdgeInsetsInsetRect(_ rect: CGRect, _ insets: UIEdgeInsets) -> CGRect | public func inset(by insets: UIEdgeInsets) -> CGRect |
UIFontDescriptor
| Swift 4 | Swift 4.2 |
| UIFontDescriptorSymbolicTraits | UIFontDescriptor.SymbolicTraits |
UIImage
| Swift 4 | Swift 4.2 |
UIKIT_EXTERN NSData * __nullable UIImagePNGRepresentation(UIImage * __nonnull image); | public func pngData() -> Data? |
NSData * __nullable UIImageJPEGRepresentation(UIImage * __nonnull image, CGFloat compressionQuality); | public func jpegData(compressionQuality: CGFloat) -> Data? |
UIApplication
| Swift 4 | Swift 4.2 |
| UIApplicationDidEnterBackground | UIApplication.didEnterBackgroundNotification |
| UIApplicationWillEnterForeground | UIApplication.willEnterForegroundNotification |
| UIApplicationDidFinishLaunching | UIApplication.didFinishLaunchingNotification |
| UIApplicationDidBecomeActive | UIApplication.didBecomeActiveNotification |
| UIApplicationWillResignActive | UIApplication.willResignActiveNotification |
| UIApplicationDidReceiveMemoryWarning | UIApplication.didReceiveMemoryWarningNotification |
| UIApplicationWillTerminate | UIApplication.willTerminateNotification |
| UIApplicationSignificantTimeChange | UIApplication.significantTimeChangeNotification |
| UIApplicationWillChangeStatusBarOrientation | UIApplication.willChangeStatusBarOrientationNotification |
| UIApplicationDidChangeStatusBarOrientation | UIApplication.didChangeStatusBarOrientationNotification |
| UIApplicationDidChangeStatusBarFrame | UIApplication.didChangeStatusBarFrameNotification |
| UIApplicationBackgroundRefreshStatusDidChange | UIApplication.backgroundRefreshStatusDidChangeNotification |
| UIApplicationProtectedDataWillBecomeUnavailable | UIApplication.protectedDataWillBecomeUnavailableNotification |
| UIApplicationProtectedDataDidBecomeAvailable | UIApplication.protectedDataDidBecomeAvailableNotification |
| UIApplicationUserDidTakeScreenshot | UIApplication.userDidTakeScreenshotNotification |
| UIApplicationOpenSettingsURLString | UIApplication.openSettingsURLString |
| UIApplicationLaunchOptionsKey | UIApplication.LaunchOptionsKey |
| UIInterfaceOrientationIsLandscape() | UIApplication.shared.statusBarOrientation.isLandscape |
UIView
| Swift 4 | Swift 4.2 |
func bringSubview(toFront view: UIView) | func bringSubviewToFront(_ view: UIView) |
| UIViewAnimationOptions | UIView.AnimationOptions() |
Foundation
NSAttributedString
| Swift 4 | Swift 4.2 |
| NSAttributedStringKey | NSAttributedString.Key |
QuartzCore
CAShapeLayer
| Swift 4 | Swift 4.2 |
| kCALineCapRound | CAShapeLayerLineCap.round |
| kCALineCapButt | CAShapeLayerLineCap.butt |
| kCALineCapSquare | CAShapeLayerLineCap.square |
| kCALineJoinMiter | CAShapeLayerLineJoin.miter |
| kCALineJoinRound | CAShapeLayerLineJoin.round |
| kCALineJoinBevel | CAShapeLayerLineJoin.bevel |
| kCAFillRuleNonZero | CAShapeLayerFillRule.nonZero |
| kCAFillRuleEvenOdd | CAShapeLayerFillRule.evenOdd |
参考资料