@interface UIButton (AsyncImage)      //size by point  - (void)setImageFromURL:(NSString *)urlString adjustToSize:(CGSize)size completion:(void (^)(void))completion logo:(UIImage *)logoImage;      @end          @implementation UIButton (AsyncImage)      - (void)setImageFromURL:(NSString *)urlString adjustToSize:(CGSize)size completion:(void (^)(void))completion logo:(UIImage *)logoImage  {      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{          UIImage *image = nil;          NSURL *url = [NSURL URLWithString:urlString];          NSData *data = [NSData dataWithContentsOfURL:url];          image = [UIImage imageWithData:data];                      if (image) {              if (!CGSizeEqualToSize(size, CGSizeZero)) {                  image = [UIImage imageWithCGImage:image.CGImage scale:[self scaleImage:image adjustToSize:size] orientation:image.imageOrientation];              }              if (logoImage) {                  image = [self addLogoImage:logoImage toImage:image];              }                              dispatch_async(dispatch_get_main_queue(), ^{                  [self setImage:image forState:UIControlStateNormal];                  completion();              });          }          else {              NSLog(@"async load error.");          }      });  }      // 缩放图片以适应按钮大小  - (CGFloat)scaleImage:(UIImage *)image adjustToSize:(CGSize)size  {      CGFloat xScale = size.width / image.size.width;      CGFloat yScale = size.height / image.size.height;              return 1.0 / MIN(xScale, yScale);  }      - (UIImage *)addLogoImage:(UIImage *)logo toImage:(UIImage *)img  {      //get image width and height      CGFloat scale = [UIScreen mainScreen].scale;      int w = scale * img.size.width;      int h = scale * img.size.height;      int logoWidth = logo.scale * logo.size.width;      int logoHeight = logo.scale * logo.size.height;      CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();              //create a graphic context with CGBitmapContextCreate      CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 4 * w, colorSpace, kCGImageAlphaPremultipliedFirst);      CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage);      CGContextDrawImage(context, CGRectMake(w - logoWidth, 0, logoWidth, logoHeight), [logo CGImage]);      CGImageRef imageMasked = CGBitmapContextCreateImage(context);      CGContextRelease(context);      CGColorSpaceRelease(colorSpace);              return [UIImage imageWithCGImage:imageMasked scale:scale orientation:img.imageOrientation];  }      @end