Detect changes on NSUserDefaults

try out the NSUserDefaultsDidChangeNotification with this code snippet:

- (id)init {  self = [super init];  if(self) {     [[NSNotificationCenter defaultCenter] addObserver:self                                              selector:@selector(defaultsChanged:)                                                  name:NSUserDefaultsDidChangeNotification                                                object:nil];  }  return self;    }- (void)defaultsChanged:(NSNotification *)notification {  // Get the user defaults  NSUserDefaults *defaults = (NSUserDefaults *)[notification object];  NSLog(@"%@", [defaults objectForKey:@"yourIntrestedObject"]);}- (void)dealloc { [[NSNotificationCenter defaultCenter] removeObserver:self];}

Use NSUserDefaultsDidChangeNotification for notification about change in User defaults:

[[NSNotificationCenter defaultCenter] addObserver:self    selector:@selector(defaultsDidChange:) name:NSUserDefaultsDidChangeNotification    object:nil];// notification- (void)defaultsDidChange:(NSNotification *)aNotification{     //}

Use KVO for notification about specific change in User defaults:

[[NSUserDefaults standardUserDefaults] addObserver:self     forKeyPath:@"APXMyPropertyIamInterestedInKey" options:NSKeyValueObservingOptionNew    context:NULL];// KVO handler-(void)observeValueForKeyPath:(NSString *)aKeyPath ofObject:(id)anObject    change:(NSDictionary *)aChange context:(void *)aContext {    // }

If you need to use this in a Swift 4 project you can use the following:

override func viewDidLoad() {    super.viewDidLoad()    NotificationCenter.default.addObserver(self, selector: #selector(defaultsChanged), name: UserDefaults.didChangeNotification, object: nil)}@objc func defaultsChanged() {    // Your code}