Difference Between Object(Forkey:) and Value(Forkey:) in Userdefaults

What is the difference between object(forKey:) and value(forKey:) in UserDefaults?

value(forKey:) is from key-value coding, and not a direct method of UserDefaults.

Never use value(forKey:) on UserDefaults or Dictionary or any other class unless you have a clearly understood need to use key-value coding to get the desired result.

When you don't have such a need, use the standard access methods provided by the class in question (such as UserDefaults object(forKey:).

UserDefaults between Objective-C and Swift

[NS]UserDefaults is backed by a plist and a dictionary. The Objective-C string was saved to the plist as a <string>Some Text</string>.

That same plist loaded in Swift gives a string for that key.

So you should have no issue using UserDefaults.string to read the value stored with Objective-C. Of course you still need to verify the value actually exists.

if let str = UserDefaults.standard.string(forKey: "textKey") {
    print("Found \(str)")
} else {
    print("No string for key")
}

Even if the original value isn't a string, using UserDefault.string is safe. It will simply return nil for non-string values.

With regard to NSDictionary and NSMutableDictionary, note that UserDefaults only retrieves immutable NSDictionary. You can't read an NSMutableDictionary (or array) from UserDefaults.

Note you can safely use a Swift dictionary to read the original NSDictionary. No need to use Objective-C classes.

Difference remove object and becoming nil for UserDefaults - Swift

No difference at all.

If you wanna remove object, use second variant for better readability

First one useful when you have an optional value and don't want care if it's nil, like

var a: String? = "hello"
UserDefaults.standard.set(a, forKey: "token")
b = nil
UserDefaults.standard.set(a, forKey: "token")

Otherwise you would have to check value and choose to either insert or delete

How can I use UserDefaults in Swift?

ref: NSUserdefault objectTypes

Swift 3 and above

Store

UserDefaults.standard.set(true, forKey: "Key") //Bool
UserDefaults.standard.set(1, forKey: "Key")  //Integer
UserDefaults.standard.set("TEST", forKey: "Key") //setObject

Retrieve

 UserDefaults.standard.bool(forKey: "Key")
 UserDefaults.standard.integer(forKey: "Key")
 UserDefaults.standard.string(forKey: "Key")

Remove

 UserDefaults.standard.removeObject(forKey: "Key")

Remove all Keys

 if let appDomain = Bundle.main.bundleIdentifier {
UserDefaults.standard.removePersistentDomain(forName: appDomain)
 }

Swift 2 and below

Store

NSUserDefaults.standardUserDefaults().setObject(newValue, forKey: "yourkey")
NSUserDefaults.standardUserDefaults().synchronize()

Retrieve

  var returnValue: [NSString]? = NSUserDefaults.standardUserDefaults().objectForKey("yourkey") as? [NSString]

Remove

 NSUserDefaults.standardUserDefaults().removeObjectForKey("yourkey")

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Register

registerDefaults: adds the registrationDictionary to the last item in every search list. This means that after NSUserDefaults has looked for a value in every other valid location, it will look in registered defaults, making them useful as a "fallback" value. Registered defaults are never stored between runs of an application, and are visible only to the application that registers them.

Default values from Defaults Configuration Files will automatically be registered.

for example detect the app from launch , create the struct for save launch

struct DetectLaunch {
static let keyforLaunch = "validateFirstlunch"
static var isFirst: Bool {
    get {
        return UserDefaults.standard.bool(forKey: keyforLaunch)
    }
    set {
        UserDefaults.standard.set(newValue, forKey: keyforLaunch)
    }
}
}

Register default values on app launch:

UserDefaults.standard.register(defaults: [
        DetectLaunch.isFirst: true
    ])

remove the value on app termination:

func applicationWillTerminate(_ application: UIApplication) {
    DetectLaunch.isFirst = false

}

and check the condition as

if DetectLaunch.isFirst {
  // app launched from first
}

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UserDefaults suite name

another one property suite name, mostly its used for App Groups concept, the example scenario I taken from here :

The use case is that I want to separate my UserDefaults (different business logic may require Userdefaults to be grouped separately) by an identifier just like Android's SharedPreferences. For example, when a user in my app clicks on logout button, I would want to clear his account related defaults but not location of the the device.

let user = UserDefaults(suiteName:"User")

use of userDefaults synchronize, the detail info has added in the duplicate answer.

How to change the type of a value from UserDefaults?

First of all, you can use UserDefaults.standar.integer(forKey:) to retrieve a value of type Int. Secondly, you should store the casted value once and shouldn't retrieve it several times (currently you retrieve it 3 times instead of just 1).

Moreover, your logic is flawed. You are trying to compare the value if the retrieved value was nil. So you are not just trying to compare Any? to Int, you are trying to compare nil to Int.

func setScore() {
    let defaults = UserDefaults.standard
    let newScore = score
    if let highScore = defaults.object(forKey: "HighScore") as? Int {
        print(highScore)
        if highScore < Int(newScore) {
            defaults.set(newScore, forKey: "HighScore")
        }
    }
}

The same function, but retrieving the Int value straight away without having to cast (UserDefaults.integer(forKey:) returns 0 if there is no value stored for that key).

func setScore() {
    let newScore = score
    if UserDefaults.standard.integer(forKey: "HighScore") < Int(newScore) {
            defaults.set(newScore, forKey: "HighScore")
        }
    }
}

NSUserDefaults - How to tell if a key exists

objectForKey: will return nil if it doesn't exist.

checking for an optional UserDefaults.standard.value

You are completely misusing optionals, forced-unwrapping, and if let.

You should also avoid using value(forKey:). And avoid needless type declarations. Let Swift infer the type when appropriate.

Your if should be:

if let facebookDetails = UserDefaults.standard.dictionary(forKey: "facebookDetails") {
}

You should also avoid the force-unwrapping unless you know for sure that the value (or cast) will always succeed.

And be consistent in your code. On one line you do:

let picture:Dictionary = (facebookDetails["picture"]  as? [String:Any])!

and another you do:

let fb_pic_data_url:String = fb_pic_data["url"] as! String

Why take two different approaches to forcing the case and the optional?

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