IOS面试题总结---先锋

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这里的问题都是面试遇到的问题也不知道答得对不对回来进行下总结以后留着用

1.定义一个入参出参都是int的block

int(^Myblock)(int) = ^(int num){return num;};

2.用GCD实现计时器

  __block int timeout=30; //倒计时时间  dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);  dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);  dispatch_source_set_timer(_timer,dispatch_walltime(NULL, 0),1.0*NSEC_PER_SEC, 0); //每秒执行  dispatch_source_set_event_handler(_timer, ^{    if(timeout<=0){ //倒计时结束，关闭      dispatch_source_cancel(_timer);      dispatch_async(dispatch_get_main_queue(), ^{        //设置界面的按钮显示 根据自己需求设置        [l_timeButton setTitle:@"发送验证码" forState:UIControlStateNormal];        l_timeButton.userInteractionEnabled = YES;      });    }else{      //int minutes = timeout / 60;      int seconds = timeout % 60;      NSString *strTime = [NSString stringWithFormat:@"%.2d", seconds];      dispatch_async(dispatch_get_main_queue(), ^{        //设置界面的按钮显示 根据自己需求设置        NSLog(@"____%@",strTime);        [l_timeButton setTitle:[NSString stringWithFormat:@"%@秒后重新发送",strTime] forState:UIControlStateNormal];        l_timeButton.userInteractionEnabled = NO;              });      timeout--;          }  });  dispatch_resume(_timer);

3.GCD处理异步

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_t group = dispatch_group_create();
dispatch_group_async(group, queue, ^{
[NSThread sleepForTimeInterval:1];
NSLog(@"group1");
});
dispatch_group_async(group, queue, ^{
[NSThread sleepForTimeInterval:2];
NSLog(@"group2");
});
dispatch_group_async(group, queue, ^{
[NSThread sleepForTimeInterval:3];
NSLog(@"group3");
});
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(@"updateUi");
});
dispatch_release(group);

4.GCD同步处理

1.串行队列 2.并行队列 3.分组 4.信号量

http://www.cnblogs.com/Quains/archive/2013/07/10/3182823.html 具体可以查看这个链接引用自这个blog

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