How to retrieve values from settings.bundle in Objective-c/Swift?

Updated for Swift 3:

func registerDefaultsFromSettingsBundle() {

    let userDefaults = UserDefaults.standard

    if let settingsURL = Bundle.main.url(forResource: "Root", withExtension: "plist", subdirectory: "Settings.bundle"),
        let settings = NSDictionary(contentsOf: settingsURL),
        let preferences = settings["PreferenceSpecifiers"] as? [NSDictionary] {

        var defaultsToRegister = [String: AnyObject]()
        for prefSpecification in preferences {
            if let key = prefSpecification["Key"] as? String,
                let value = prefSpecification["DefaultValue"] {

                defaultsToRegister[key] = value as AnyObject
                debugPrint("registerDefaultsFromSettingsBundle: (\(key), \(value)) \(type(of: value))")
            }
        }

        userDefaults.register(defaults: defaultsToRegister)

    } else {
        debugPrint("registerDefaultsFromSettingsBundle: Could not find Settings.bundle")
    }
}

Although you define the defaults settings, they are not really stored as a value. They are stored as default. If you try to read it, the value is null. Default setting is another property as value is. But it doesnt mean that will write the default value as a default.

What I do is, first, check if some setting,(that I'm sure that should have a value) has anything stored on it. If it doesn't have anything then I write all the defaults.

Here is an example.

on AppDelegate.m I check if email_notificaciones_preference has a value, if not, I write ALL default settings to each setting.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
    NSUserDefaults * standardUserDefaults = [NSUserDefaults standardUserDefaults];
    NSString * email_notificaciones_preference = [standardUserDefaults objectForKey:@"email_notificaciones_preference"];
    if (!email_notificaciones_preference) {
        [self registerDefaultsFromSettingsBundle];
    }

}

This function is what I use to write defaults to each element.

#pragma NSUserDefaults
- (void)registerDefaultsFromSettingsBundle {
    // this function writes default settings as settings
    NSString *settingsBundle = [[NSBundle mainBundle] pathForResource:@"Settings" ofType:@"bundle"];
    if(!settingsBundle) {
        NSLog(@"Could not find Settings.bundle");
        return;
    }

    NSDictionary *settings = [NSDictionary dictionaryWithContentsOfFile:[settingsBundle stringByAppendingPathComponent:@"Root.plist"]];
    NSArray *preferences = [settings objectForKey:@"PreferenceSpecifiers"];

    NSMutableDictionary *defaultsToRegister = [[NSMutableDictionary alloc] initWithCapacity:[preferences count]];
    for(NSDictionary *prefSpecification in preferences) {
        NSString *key = [prefSpecification objectForKey:@"Key"];
        if(key) {
            [defaultsToRegister setObject:[prefSpecification objectForKey:@"DefaultValue"] forKey:key];
            NSLog(@"writing as default %@ to the key %@",[prefSpecification objectForKey:@"DefaultValue"],key);
        }
    }

    [[NSUserDefaults standardUserDefaults] registerDefaults:defaultsToRegister];

}

Hope that helps.

If anyone needs it - I translated the answer from MIQUEL to Swift (as good as I could as I'm still learning) :

var standardUserDefaults = NSUserDefaults.standardUserDefaults()
var us: AnyObject? = standardUserDefaults.objectForKey("your_preference")
if us==nil {
    self.registerDefaultsFromSettingsBundle();
}

And the func registerDefaultsFromSettingsBundle:

func registerDefaultsFromSettingsBundle() {
    // this function writes default settings as settings
    var settingsBundle = NSBundle.mainBundle().pathForResource("Settings", ofType: "bundle")
    if settingsBundle == nil {
        NSLog("Could not find Settings.bundle");
        return
    }
    var settings = NSDictionary(contentsOfFile:settingsBundle!.stringByAppendingPathComponent("Root.plist"))!
    var preferences: [NSDictionary] = settings.objectForKey("PreferenceSpecifiers") as [NSDictionary];
    var defaultsToRegister = NSMutableDictionary(capacity:(preferences.count));

    for prefSpecification:NSDictionary in preferences {
        var key: NSCopying? = prefSpecification.objectForKey("Key") as NSCopying?
        if key != nil {
            defaultsToRegister.setObject(prefSpecification.objectForKey("DefaultValue")!, forKey: key!)
        }
    }
    NSUserDefaults.standardUserDefaults().registerDefaults(defaultsToRegister);  
}