[NSNotification] #Objective-C

.m

- (void)addNotification {
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(applicationDidBecomeActive) name:UIApplicationDidBecomeActiveNotification
                                               object:nil];
    
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(applicationWillResignActive)
                                                 name: UIApplicationWillResignActiveNotification
                                               object:nil];
}

- (void)removeNotification {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

- (void)applicationWillResignActive {

}

- (void)applicationDidBecomeActive {

}