iOS 13 用户默认值 : app crash on start on some devices

Question

iOS 13 上的应用程序在某些设备上启动时崩溃。该应用程序正在生产中，我在 Xcode Organizer Crashes 中看到了这个问题。我无法在模拟器或任何物理设备上重现此问题。

我想这与本地化有关。我使用“AppleLanguages”键并将所选语言保存为数组。我将用户默认设置中的语言保存为:

static var language: Language {
    get {

        if UserDefaults.standard.bool(forKey: isLanguageSelectedKey) {
            if let languageCode = UserDefaults.standard.array(forKey: appleLanguagesKey)?.first,
                let language = Language(rawValue: languageCode as! String) {
                return language
            } else {

                return Language.someLanguage
            }
        } else {
            return Language.someLanguage
        }

    }

    set {
        guard language != newValue else {
            return
        }
        UserDefaults.standard.removeObject(forKey: appleLanguagesKey)
        UserDefaults.standard.synchronize()

        UserDefaults.standard.set([newValue.rawValue], forKey: appleLanguagesKey)

        UserDefaults.standard.synchronize()
    }

我在 Xcode Organizer Crashes 中看到的 Stacktrace 是:

Last Exception Backtrace (0)
0   (null) in __exceptionPreprocess ()
-------------------------------------------------------
8   (null) in +[NSUserDefaults(NSUserDefaults) standardUserDefaults] ()
9   (null) in __45+[GMSx_GTMSessionFetcher fetcherUserDefaults]_block_invoke ()
10  (null) in _dispatch_client_callout ()
11  (null) in _dispatch_once_callout ()
12  (null) in +[GMSx_GTMSessionFetcher fetcherUserDefaults] ()
13  (null) in +[GMSx_GTMSessionFetcher fetchersForBackgroundSessions] ()
14  (null) in +[GMSx_GTMSessionFetcher load] ()
15  (null) in load_images ()
-------------------------------------------------------



Thread 1
0   (null) in __pthread_kill ()
-------------------------------------------------------
9   (null) in _dispatch_once_callout ()
10  (null) in +[GMSx_GTMSessionFetcher fetcherUserDefaults] ()
11  (null) in +[GMSx_GTMSessionFetcher fetchersForBackgroundSessions] ()
12  (null) in +[GMSx_GTMSessionFetcher load] ()
13  (null) in load_images ()
-------------------------------------------------------

Answer 1

我没有所有的东西，所以这里有一些假设可能没有得到妥善解决:

static var language: Language {
get {
        if UserDefaults.standard.bool(forKey: isLanguageSelectedKey),
             let languageCode = UserDefaults.standard.array(forKey: appleLanguagesKey)?.first as? string,
             let language = Language(rawValue: languageCode) {
                return language
        }
        // No language value found, so return someLanguage
        return Language.someLanguage

    }
set {
    guard language != newValue else {
        return
    }
    UserDefaults.standard.removeObject(forKey: appleLanguagesKey)
    UserDefaults.standard.set([newValue.rawValue], forKey: appleLanguagesKey)
}

做了什么？

1. languageCode 现在已安全解包以避免强制转换，这可能会导致崩溃
2. 重写了 if 语句，使其更加简洁，并消除了导致 Language.someLanguage 返回的情况
3. 我删除了你的 setter 中的 synchonize() 调用