通知

通知的定义
//定义通知名
static NSString * const AFNSURLSessionTaskDidResumeNotification  = @"com.alamofire.networking.nsurlsessiontask.resume";
static NSString * const AFNSURLSessionTaskDidSuspendNotification = @"com.alamofire.networking.nsurlsessiontask.suspend";

//发送通知
[[NSNotificationCenter defaultCenter] postNotificationName:AFNSURLSessionTaskDidResumeNotification object:self];

//注册通知监听者
- (void)addNotificationObserverForTask:(NSURLSessionTask *)task {
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(taskDidResume:) name:AFNSURLSessionTaskDidResumeNotification object:task];
}

//移除通知的监听者（不做移除操作，不会产生崩溃和循环引用）
- (void)removeNotificationObserverForTask:(NSURLSessionTask *)task {
    [[NSNotificationCenter defaultCenter] removeObserver:self name:AFNSURLSessionTaskDidSuspendNotification object:task];
}

KVO的定义：

//注册监听者
[self.courseTableView addObserver:self forKeyPath:@"contentOffset" options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context:nil];

//实现监听方法 
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {
    if ([keyPath isEqualToString:@"contentOffset"]) {
        NSLog(@"object = %@", object);
    }
}
//移除监听者（不移除程序崩溃）
- (void)dealloc
{
    [self.courseTableView removeObserver:self forKeyPath:@"contentOffset"];
}

UIControl和UIView的关系：
UITableView : UIScrollView
UIScrollView : UIView
UIView : UIResponder
UIResponder : NSObject

UIButton : UIControl
UIControl : UIView
UIView : UIResponder
UIResponder : NSObject