Delete all keys from a NSUserDefaults dictionary i

Question

I use the NSUserDefaults dictionary to store basic information such as high scores etc so that when the user closes the app data is not lost. Anyways I use:

NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];

to store data. If I wish to store a new high score for example then I would do:

[prefs setInteger:1023 forKey:@"highScore"];
[prefs synchronize];  //this is needed in case the app is closed. 

and later if I wish to retrieve the high score I would do:

[prefs integerForKey:@"highScore"];

anyways the point is that I store a lot of other things because the NSUserDefaults enable you to store booleans, integers, objects etc. what method would I have to execute to delete all keys so that NSUserDefaults becomes like the fist time I launch the app?

I am looking for something like:

NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
[prefs deleteAllKeysAndObjectsInTheDictionary];

or maybe there is a way of getting all keys and I have to loop through each object but I don't know how to remove them.

EDIT:

I have tried :

NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
[NSUserDefaults resetStandardUserDefaults];
[prefs synchronize];

and I still am able to retrieve a high score....

Answer 1

+ (void) resetStandardUserDefaults doesn't persist the changes, it simply resets the in-memory user defaults object so that the next synchronize call will read from the on-disk copy, instead of overwriting existing in-memory values with the on-disk versions.

Iterating over the keys is better, but there's actually a function that does this for you: removePersistentDomainForName:.

// you can usually get the domain via [[NSBundle mainBundle] bundleIdentifier]
[[NSUserDefaults standardUserDefaults]
 removePersistentDomainForName:[[NSBundle mainBundle] bundleIdentifier]];
// or use a string for any other settings domains you use
//[[NSUserDefaults standardUserDefaults]
// removePersistentDomainForName:@"com.mycompany.myappname"];
[[NSUserDefaults standardUserDefaults] synchronize];

At the end of the synchronize operation, both the disk and memory copies of user defaults will contain none of the values set by your application.

Answer 2

Shortest way to do this with the same results like in Alex Nichol's top answer:

NSString *appDomain = NSBundle.mainBundle.bundleIdentifier;
[[NSUserDefaults standardUserDefaults] removePersistentDomainForName:appDomain];
[[NSUserDefaults standardUserDefaults] synchronize];

Answer 3

Swift

 func resetUserDefaults(){

    let userDefaults = NSUserDefaults.standardUserDefaults()
    let dict = userDefaults.dictionaryRepresentation() as NSDictionary

    for key in dict.allKeys {

            userDefaults.removeObjectForKey(key as! String)
    }

    userDefaults.synchronize()

}

Answer 4

Oneliner in Swift:

Swift 3

NSUserDefaults.standardUserDefaults().removePersistentDomainForName(
NSBundle.mainBundle().bundleIdentifier!)

Swift 4

UserDefaults.standard.removePersistentDomain(forName: Bundle.main.bundleIdentifier!)

Answer 5

Does this method not do that:

+ (void)resetStandardUserDefaults

From the documentation for NSUserDefaults:

resetStandardUserDefaults

Synchronizes any changes made to the shared user defaults object and releases it from memory.

+ (void)resetStandardUserDefaults

Discussion

A subsequent invocation of standardUserDefaults creates a new shared user defaults object with the standard search list.

Based on this, you can do:

[NSUserDefaults resetStandardUserDefaults];
[NSUserDefaults standardUserDefaults];

and now the defaults should be reset.

Answer 6

Swift 3 or 4 We can even simplify described snippet into this modern expression:

func clearAll() {
    let settingsDictionary = userDefaults.dictionaryRepresentation()
    settingsDictionary.forEach { key, _ in userDefaults.removeObject(forKey: key) }
    userDefaults.synchronize()
}