什么是使用NSUserDefaults.standardUserDefaults（）。registerDefaults（Dictionary <String, AnyObject> ）？

Question

I have 4 user settings in the app which are independent of each other. I want to check value for each setting using appropriate method of NSUserDefaults.standardUserDefaults() for each key and if any of the key is not found in user defaults then register the default predefined value.

I do not want to call NSUserDefaults.standardUserDefaults.registerDefaults(Dictionary<String, AnyObject>) every time with app launch , so i am not registering defaults using this method in AppDelegate.Swift- didFinishLaunchingWithOptions with every app launch but i call a method in root view controller's viewDidLoad() which runs a custom logic to check each user settings. if all 4 settings already saved by user no call to registerDefaults() at all and if any one of settings not saved, call registerDefaults() .

Can anyone suggest is there any effective way of doing this or comment on the way i am trying to achieve it ? Will Apple review team approve my logic?

I want to get rid of too many IF 's. Below is the logic i have written :-

    let userDefaults = NSUserDefaults.standardUserDefaults() as NSUserDefaults

    rate = AVSpeechUtteranceDefaultSpeechRate
    speech = true
    language = AVSpeechSynthesisVoice.currentLanguageCode()
    defaultLanguageName = NSLocale.currentLocale().displayNameForKey(NSLocaleIdentifier, value: language)
    bttnEffect = "Pop"

    var defaultSpeechSettings: Dictionary<String, AnyObject> = ["speechRate": rate, "speech": speech, "languageCode": language, "defLanguageLabel": defaultLanguageName, "gender": bttnEffect ]

    var isSpeechRateSettingLoaded = false
    var isSpeechSettingLoaded = false
    var isLangSettingLoaded = false
    var isBttnEffectSettingLoaded = false

    if let theRate: Float = userDefaults.valueForKey("speechRate") as? Float {
        rate = theRate
        defaultSpeechSettings.removeValueForKey("speechRate")
         isSpeechRateSettingLoaded = true
    }
    if let toggleVal: Bool = userDefaults.valueForKey("speech") as? Bool {
        speech = toggleVal
        defaultSpeechSettings.removeValueForKey("speech")
         isSpeechSettingLoaded = true
    }
    if let langCode = userDefaults.stringForKey("languageCode") {
        language = langCode
        defaultSpeechSettings.removeValueForKey("languageCode")
        defaultSpeechSettings.removeValueForKey("defLanguageLabel")
        isLangSettingLoaded = true
    }
    if let effectStyle = userDefaults.stringForKey("bttnEffect") {
        bttnEffect = effectStyle
        defaultSpeechSettings.removeValueForKey("bttnEffect")
        isBttnEffectSettingLoaded = true
    }
    if !(isSpeechRateSettingLoaded && isSpeechSettingLoaded && isLangSettingLoaded && isBttnEffectSettingLoaded) {
        NSUserDefaults.standardUserDefaults().registerDefaults(defaultSpeechSettings)
    }

Answer 1

Apple's review team doesn't care if you write sloppy code.

Note Ken's comment about how registerDefaults() only affects return values if no value is set for the given key.

Aside from that, however, extensions are a nice way to tame NSUserDefaults.

extension NSUserDefaults {
    private static let speechRateKey = "speechRate"
    var speechRate: Float {
        get {
            return valueForKey(NSUserDefaults.speechRateKey) as? Float ?? AVSpeechUtteranceDefaultSpeechRate
        }
        set {
            setObject(newValue, forKey: NSUserDefaults.speechRateKey)
            synchronize()
        }
    }
}

// somewhere else:
let speechRate = NSUserDefaults.standardUserDefaults().speechRate
doSomethingWith(speechRate)
NSUserDefaults.standardUserDefaults().speechRate = getNewSpeechRate()