OC原理之多线程(一)

对于如下的代码，打印结果是什么

dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    dispatch_async(queue, ^{
        NSLog(@"1");
        [self performSelector:@selector(testhaha) withObject:nil afterDelay:.0];
        NSLog(@"3");
});

- (void)testhaha {
    NSLog(@"2");
}

运行之后打印如下:

2021-02-23 23:14:10.384150+0800 KVOTest[17526:624011] 1
2021-02-23 23:14:10.384456+0800 KVOTest[17526:624011] 3

从打印结果来看,2并没有打印，究其原因是,performSelector:withObject:afterDelay:的本质是往Runloop中添加定时器,但是子线程中的runloop默认是没有启动的

可通过如下的代码:

dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
    dispatch_async(queue, ^{
        NSLog(@"1");
        [self performSelector:@selector(testhaha) withObject:nil afterDelay:.0];
        [[NSRunLoop currentRunLoop] run];
        NSLog(@"3");
 });

- (void)testhaha {
    NSLog(@"2");
}

或者直接放在主线程中执行:

dispatch_queue_t queue = dispatch_get_main_queue();
    dispatch_async(queue, ^{
        NSLog(@"1");
        [self performSelector:@selector(testhaha) withObject:nil afterDelay:.0];
        [[NSRunLoop currentRunLoop] run];
        NSLog(@"3");
 });

- (void)testhaha {
    NSLog(@"2");
}