通知PostNotification

//
//  ViewController.m
//  FKLTest
//
//  Created by kun on 16/8/10.
//  Copyright © 2016年 kun. All rights reserved.
//

#import "ViewController.h"
#import "FKLTool.h"
#import "XMGDownloadTool.h"
#import "PostNotificationViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    NSLog(@"******#receiveNotification--Begin#******");
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(receiveNotification) name:@"postNotification" object:nil];
    NSLog(@"******#receiveNotification--End#******");

}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    PostNotificationViewController *postVc = [[PostNotificationViewController alloc] init];
    
    [self presentViewController:postVc animated:YES completion:nil];
}

- (void)receiveNotification
{
    NSLog(@"---begin---%s", __func__);
    sleep(5.0);
    NSLog(@"---after---%s", __func__);
}

@end

//
//  PostNotificationViewController.m
//  FKLTest
//
//  Created by kun on 16/8/24.
//  Copyright © 2016年 kun. All rights reserved.
//

#import "PostNotificationViewController.h"

@interface PostNotificationViewController ()

@end

@implementation PostNotificationViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"******#postNotification--Begin#******");
    [[NSNotificationCenter defaultCenter] postNotificationName:@"postNotification" object:nil];
    NSLog(@"******#postNotification--End#******");
}

@end

2016-08-24 18:54:07.713 FKLTest[1186:24510] ******#receiveNotification--Begin#******
2016-08-24 18:54:07.714 FKLTest[1186:24510] ******#receiveNotification--End#******
2016-08-24 18:56:15.805 FKLTest[1186:24510] ******#postNotification--Begin#******
2016-08-24 18:56:15.806 FKLTest[1186:24510] ---begin----[ViewController receiveNotification]
2016-08-24 18:56:20.807 FKLTest[1186:24510] ---after----[ViewController receiveNotification]
2016-08-24 18:56:20.808 FKLTest[1186:24510] ******#postNotification--End#******

分析：监听通知必须要在发送通知之前设置好。发送通知，如果有监听此通知的观察者，会等待观察者的监听方法处理完后才会返回；如果没有则立马返回。