NSOperation实现线程间通信

 -(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
 {
     //1.创建队列
     NSOperationQueue *queue= [[NSOperationQueue alloc]init];

     NSBlockOperation *download1 = [NSBlockOperation blockOperationWithBlock:^{
         //2.1.确定要下载网络图片的url地址，一个url唯一对应着网络上的一个资源
         NSURL *url = [NSURL URLWithString:@"http://p6.qhimg.com/t01d2954e2799c461ab.jpg"];

         //2.2.根据url地址下载图片数据到本地（二进制数据)
         NSData *data = [NSData dataWithContentsOfURL:url];

         //2.3.把下载到本地的二进制数据转换成图片
        self.image1 = [UIImage imageWithData:data];

     }];

     NSBlockOperation *download2 = [NSBlockOperation blockOperationWithBlock:^{
         //2.1.确定要下载网络图片的url地址，一个url唯一对应着网络上的一个资源
         NSURL *url = [NSURL URLWithString:@"http://p6.qhimg.com/t01d2954e2799c461ab.jpg"];

         //2.2.根据url地址下载图片数据到本地（二进制数据)
         NSData *data = [NSData dataWithContentsOfURL:url];

         //2.3.把下载到本地的二进制数据转换成图片
         self.image2 = [UIImage imageWithData:data];

     }];

     NSBlockOperation *combie = [NSBlockOperation blockOperationWithBlock:^{

         UIGraphicsBeginImageContext(CGSizeMake(, ));

         [self.image1 drawInRect:CGRectMake(, , , )];
         [self.image2 drawInRect:CGRectMake(, , , )];

         UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

         UIGraphicsEndImageContext();

         //刷新UI
         [[NSOperationQueue mainQueue] addOperationWithBlock:^{
             self.imageView.image = image;
             NSLog(@"%@----",[NSThread currentThread]);
         }];

     }];

     [combie addDependency:download1];
     [combie addDependency:download2];

     [queue addOperation:download1];
     [queue addOperation:download2];
     [queue addOperation:combie];
 }

示例