NSUserDefaults removeObjectForKey vs. setObject:nil

Yes, both lines of code are equivalent, both will result in nil read

id obj = [[NSUserDefaults standardUserDefaults] objectForKey:@"example key"];

NSUserDefaults will return nil if the key was not found. I would recommend to use the removeObjectForKey instead of setting it to nil.

here is how to test if setting key value to nil removed the key entry from NSUserDefaults standardUserDefaults.

NSArray *keys = [[[NSUserDefaults standardUserDefaults] dictionaryRepresentation] allKeys] copy];
   for(NSString *key in keys) {
       NSLog(@"Key Name: %@", key);
}
[keys release];

or simply dump the key/value dictionary of NSUserDefaults standardUserDefaults

NSLog(@"All contents of NSUserDefaults: %@", [[NSUserDefaults standardUserDefaults] dictionaryRepresentation]);

Swift 3.0

The below answer is no longer the case when I tested this. When set to nil the result is NSCFData being stored. Possibly an NSNull object reference, but I am not positive.

To completely remove a value for a key use UserDefaults.standard.removeObject(forKey: "YourDefault")

I tested with the following code:

UserDefaults.standard.set(["a", "b", "c"], forKey: "MyDefaults")
print("Test A: My saved defaults \(UserDefaults.standard.object(forKey: "MyDefaults"))")

UserDefaults.standard.set(nil, forKey: "MyDefaults")
print("Test B: My defaults set to nil \(UserDefaults.standard.object(forKey: "MyDefaults"))")

UserDefaults.standard.removeObject(forKey: "MyDefaults")
print("Test C: My defaults removed \(UserDefaults.standard.object(forKey: "MyDefaults"))")