- (void)viewDidLoad {

[super viewDidLoad];

// Do any additional setup after loading the view.

self.title=@"测试类";

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

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

NSLog(@"子线程注册通知===%@",[NSThread currentThread]);

});

NSLog(@"主线程===%@",[NSThread currentThread]);

UIButton *sendBtn=[[UIButton alloc] initWithFrame:CGRectMake(100, 100, 100, 50)];

sendBtn.backgroundColor=[UIColor redColor];

[sendBtn setTitle:@"发送通知" forState:UIControlStateNormal];

[sendBtn addTarget:self action:@selector(sendNoti) forControlEvents:UIControlEventTouchUpInside];

[self.view addSubview:sendBtn];

// Do any additional setup after loading the view.

}

-(void)sendNoti

{

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

[[NSNotificationCenter defaultCenter] postNotificationName:@"xxx" object:nil];

NSLog(@"发送通知子线线程===%@",[NSThread currentThread]);

});

}

-(void)xxx

{

NSLog(@"收到通知线程===%@",[NSThread currentThread]);

}

打印结果：

1、子线程注册 子线程发送

主线程==={number = 1, name = main}

子线程注册通知==={number = 3, name = (null)}

收到通知线程==={number = 4, name = (null)}

发送通知子线线程==={number = 4, name = (null)}

2、主线程注册 子线程发送

主线程注册通知==={number = 1, name = main}

收到通知线程==={number = 3, name = (null)}

发送通知子线线程==={number = 3, name = (null)}

结论：

不管你在哪个线程注册通知，发送通知在哪个线程，接受通知就会在哪个线程，即发送通知和接受通知在同一个线程，因此，若要更新UI的操作时，需要切入主线程

注意：通知触发的方法是同步执行，所以通知会有延迟