Clearing NSUserDefaults

Question

You can remove the application's persistent domain like this:

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

In Swift 3 and later:

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

This is similar to the answer by @samvermette but is a little bit cleaner IMO.

This code resets the defaults to the registration domain:

[[NSUserDefaults standardUserDefaults] setPersistentDomain:[NSDictionary dictionary] forName:[[NSBundle mainBundle] bundleIdentifier]];

In other words, it removeObjectForKey for every single key you ever registered in that app.

Credits to Ken Thomases on this Apple Developer Forums thread.

Did you try using -removeObjectForKey?

 [[NSUserDefaults standardUserDefaults] removeObjectForKey:@"defunctPreference"];

Here is the answer in Swift:

let appDomain = NSBundle.mainBundle().bundleIdentifier!
NSUserDefaults.standardUserDefaults().removePersistentDomainForName(appDomain)

If you need it while developing, you can also reset your simulator, deleting all the NSUserDefaults.

iOS Simulator -> Reset Content and Settings...

Bear in mind that it will also delete all the apps and files on simulator.