看过的文章

KVO 底层本质:https://www.jianshu.com/p/5e3bb16e4d1b
第一、weakSelf 的宏定义写法

#define WeakObj(obj) __weak typeof(obj) o##Weak = obj;

第二、为什么子线程 runLoop 无法开启

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event

dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"1");
        [[NSRunLoop currentRunLoop]run];
        [self performSelector:@selector(test) withObject:nil afterDelay:0];
        NSLog(@"2");
    });
}
-(void)test
{
    NSLog(@"3");
}

打印结果:
2019-10-12 10:16:58.930673+0800 测试 switch[13229:1170138] 1
2019-10-12 10:16:58.930969+0800 测试 switch[13229:1170138] 2

因为run方法只是尝试想要开启当前线程中的runloop，但是如果该线程中并没有任何事件(source、timer、observer)的话，并不会成功的开启

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event

dispatch_async(dispatch_get_global_queue(0, 0), ^{
        NSLog(@"1");
        [self performSelector:@selector(test) withObject:nil afterDelay:0];
         [[NSRunLoop currentRunLoop]run];
        NSLog(@"2");
    });
}

打印结果:
2019-10-12 10:20:55.758207+0800 测试 switch[13268:1174223] 1
2019-10-12 10:20:55.758506+0800 测试 switch[13268:1174223] 3
2019-10-12 10:20:55.758620+0800 测试 switch[13268:1174223] 2

第三、performSelector: xxx onThread: xxx withObject: xxx waitUntilDone: xxx 的 waitUntilDone 的作用

它的作用是 是否阻塞当前所执行的线程

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
    NSLog(@"start");
   [self performSelector:@selector(helloAction) onThread:[NSThread currentThread] withObject:nil waitUntilDone:YES];
    NSLog(@"end");
}
-(void)helloAction
{
    NSLog(@"等待5秒");
    sleep(5);
}

打印结果:
2019-10-12 15:27:56.569041+0800 测试 switch[15403:1375791] start
2019-10-12 15:27:56.569226+0800 测试 switch[15403:1375791] 等待5秒
.
.
.
2019-10-12 15:28:01.569464+0800 测试 switch[15403:1375791] end

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
    NSLog(@"start");
    [self performSelector:@selector(helloAction) onThread:[NSThread       
    currentThread] withObject:nil waitUntilDone:NO];
    NSLog(@"end");
}
-(void)helloAction
{
    NSLog(@"等待5秒");
    sleep(5);
}

打印结果:
2019-10-12 15:32:58.978556+0800 测试 switch[15455:1380883] start
2019-10-12 15:32:58.979096+0800 测试 switch[15455:1380883] end
2019-10-12 15:32:58.979548+0800 测试 switch[15455:1380883] 等待5秒