iOS 面试题~经验找代码错误

//联系人:石虎QQ:1224614774昵称:嗡嘛呢叭咪哄

一、概念

1.指出以下这段代码的问题

- (void)test{

CGRectframe =CGRectMake(20,200,200,20);

self.alert = [[UILabel alloc]initWithFrame:frame];

self.alert.text =@"Please wait 10 seconds...";

self.alert.textColor = [UIColor redColor];

[self.view addSubview:self.alert];

NSOperationQueue*waitQueue = [[NSOperationQueuealloc]init];

[waitQueueaddOperationWithBlock:^{

[NSThreadsleepUntilDate:[NSDatedateWithTimeIntervalSinceNow:10]];

self.alert.text =@"石虎";

NSLog(@"执行一个新的操作，线程：%@", [NSThread currentThread]);

}];

}

正确修改为:

[waitQueueaddOperationWithBlock:^{

[NSThreadsleepUntilDate:[NSDatedateWithTimeIntervalSinceNow:10]];

//正确要在主线程赋

dispatch_async(dispatch_get_main_queue(), ^{

self.alert.text =@"石虎";

});

NSLog(@"执行一个新的操作，线程：%@", [NSThread currentThread]);

}];

2.写出下列程序的输出结果

typedefvoid(^BoringBlock)(void);

intmain(intargc,constchar*argv[])

{

inta =23;

__blockintb =23;

BoringBlock block1 = ^{NSLog(@"a1==%d",a);};

BoringBlock block2 = ^{NSLog(@"b1==%d",b);};

a =32;

b =32;

BoringBlock block3 = ^{NSLog(@"a1==%d",a);};

BoringBlock block4 = ^{NSLog(@"b2==%d",b);};

block1();

block2();

block3();

block4();

return0;

}

打印结果:

2017-10-3020:29:25.645石虎测试 demo[969:6507971] a1==23

2017-10-3020:29:25.646石虎测试 demo[969:6507971] b1==32

2017-10-3020:29:25.646石虎测试 demo[969:6507971] a1==32

2017-10-3020:29:25.646石虎测试 demo[969:6507971] b2==32

谢谢!!!