iOS开发进阶(iOS开发实战：GCD)summary

多线程：我们一般把耗时操作放到子线程来执行，然后主线程只做UI操作

GCD是苹果开发的一个多核编程的解决办法，和(NSThread、NSOperationQueue、NSInvocationOperation)多线程技术方案相比，使用起来更加简单和方便

//网络显示图片

  self.indicator.hidden = NO;

  [self.indicator startAnimating];

  //进入异步线程

  dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

      //异步下载图片

      NSURL * url = [NSURL URLWithString:@"http://anImageUrl"];

      NSData * data = [NSData dataWithContentsOfURL:url];

      //网络请求之后进入主线程

      dispatch_async(dispatch_get_main_queue(), ^{

          //关闭loading

          [self.indicator stopAnimating];

          self.indicator.hidden = YES;

          if (data) {//显示图片

              self.imageView.image = [UIImage imageWithData:data];

          }

      });

  });

 

// 延迟执行：

    double delayInSeconds = 2.0;

    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);

    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){

        // code to be executed on the main queue after delay

    });

 

 

利用GCD并行多个线程并且等待所有线程结束之后再执行其它任务

dispatch_group_t group = dispatch_group_create();

   dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{

       // 并行执行的线程一

   });

   dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{

       // 并行执行的线程二

   });

   dispatch_group_notify(group, dispatch_get_global_queue(0,0), ^{

       // 汇总结果

   });