GCD加載圖片並按比例拉伸展示

 dispatch_async(dispatch_get_global_queue(0, 0), ^{
        //處理的耗時操作
        NSData *data = [NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://192.168.1.67:8080/img/luckgo_spxq.png"]];
        //通知主線程刷新
        dispatch_async(dispatch_get_main_queue(), ^{
            UIImage *image = [UIImage imageWithData:data];
            CGSize size = image.size;
            CGFloat width = size.width;
            CGFloat height = size.height;
            CGFloat scale = height/width;
            
            CGFloat scaledWidth = SCREEN_WIDTH;
            CGFloat scaledHeight = SCREEN_WIDTH * scale;
            UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 64, scaledWidth, scaledHeight)];
            imageView.image = image;
            [self.view addSubview:imageView];
        });
    });

        });

    });