NSNotificationCenter通知中心是同步操作还是异步操作

题目

通知中心是同步操作还是异步操作？

代码实现

- (void)viewDidLoad
{
    [super viewDidLoad];

self.btn = [UIButton buttonWithType:UIButtonTypeCustom];

CGFloat x,y,w,h;
    x = 100;
    y = 100;
    w = 100;
    h = 100;

self.btn.frame = (CGRect){x,y,w,h};
self.btn.backgroundColor = [UIColor redColor];
    [self.view addSubview:self.btn];

    [self.btn addTarget:self action:@selector(btnClick) forControlEvents:UIControlEventTouchUpInside];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(dosth) name:@"click" object:nil];

}

- (void)dosth
{

 //同步
 NSLog(@"收到通知");
 sleep(3);
 NSLog(@"处理通知完毕");

 //异步
 /*
 dispatch_async(dispatch_get_global_queue(0, 0), ^{
NSLog(@"收到通知");
sleep(3);
NSLog(@"异步-处理通知完毕");
 });
 */
}

-(void)btnClick
{
    //同步
    NSLog(@"开始");
[[NSNotificationCenter defaultCenter] postNotification:[NSNotification notificationWithName:@"click" object:nil userInfo:nil]];
    NSLog(@"结束");

    //异步
    /*
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
         NSLog(@"异步-开始");
[[NSNotificationCenter defaultCenter] postNotification:[NSNotification notificationWithName:@"click" object:nil userInfo:nil]];
         NSLog(@"异步-结束");
    });
     */
}

可以在post地方打个断点，会发现通知中心是同步的。

当然也可以做成异步处理。