NSNotificationCenter NSNotificationQueue 同步？异步？

NSNotificationCenter NSNotificationQueue 同步？异步？

刚同事问一个问题，想起了一道面试题目，说是通知发送接受过程是同步还是异步。记得是同步，写个demo证实下

#import "NotificationViewController.h"
#define NOTIFICATIONNAME @"NSNotificationCenter__"
@interface NotificationViewController ()

@end

@implementation NotificationViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
    button.frame = CGRectMake(0, 0, 100, 100);
    button.backgroundColor = [UIColor redColor];
    [button addTarget:self action:@selector(buttonClick) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(addObserver) name:NOTIFICATIONNAME object:nil];
}
- (void)buttonClick {
    NSLog(@"开始postNotificationName==%@",[[NSThread currentThread]description]);
    [[NSNotificationCenter defaultCenter] postNotificationName:NOTIFICATIONNAME object:nil];
    NSLog(@"结束postNotificationName==%@",[[NSThread currentThread]description]);
}
- (void)addObserver
{
    NSLog(@"接收到消息==%@",[[NSThread currentThread]description]);
    NSLog(@"睡眠5秒");
    sleep(5);
}

@end

结果验证了是同步的

开始postNotificationName=={number = 1, name = main}
接收到消息=={number = 1, name = main}
睡眠5秒
结束postNotificationName=={number = 1, name = main}

如果不想同步等待呢，除了另起一个线程，还有一个NSNotificationQueue可以来实现

#import "NotificationViewController.h"
#define NOTIFICATIONNAME @"NSNotificationCenter__"
@interface NotificationViewController ()

@end

@implementation NotificationViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    UIButton *button1 = [UIButton buttonWithType:UIButtonTypeSystem];
    button1.frame = CGRectMake(200, 0, 100, 100);
    button1.backgroundColor = [UIColor redColor];
    [button1 addTarget:self action:@selector(buttonClick1) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button1];
    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(addObserver) name:NOTIFICATIONNAME object:nil];
}

- (void)addObserver
{
    NSLog(@"接收到消息==%@",[[NSThread currentThread]description]);
    NSLog(@"睡眠5秒");
    sleep(5);
}


- (void)buttonClick1
{
    NSLog(@"开始postNotificationName==%@",[[NSThread currentThread]description]);
    NSNotification *noti = [NSNotification notificationWithName:NOTIFICATIONNAME object:nil];
    [[NSNotificationQueue defaultQueue] enqueueNotification:noti postingStyle:NSPostASAP];
//这里有同步异步参数，NSPostASAP，NSPostNow
    NSLog(@"结束postNotificationName==%@",[[NSThread currentThread]description]);
}
@end

开始postNotificationName=={number = 1, name = main}
结束postNotificationName=={number = 1, name = main}
接收到消息=={number = 1, name = main}
睡眠5秒