載入網路圖片時，根據Url獲取圖片的尺寸進行UI佈局。

可將方法+ (CGSize)getImageSizeWithURL:(id)URL;放在UIImage的分類中。

引入系統的ImageIO.framework

/**
 *  根據圖片url獲取圖片尺寸
 */
+ (CGSize)getImageSizeWithURL:(id)URL{
    NSURL * url = nil;
    if ([URL isKindOfClass:[NSURL class]]) {
        url = URL;
    }
    if ([URL isKindOfClass:[NSString class]]) {
        url = [NSURL URLWithString:URL];
    }
    if (!URL) {
        return CGSizeZero;
    }
    CGImageSourceRef imageSourceRef =     CGImageSourceCreateWithURL((CFURLRef)url, NULL);
    CGFloat width = 0, height = 0;
    if (imageSourceRef) {
        CFDictionaryRef imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSourceRef, 0, NULL);
      if (imageProperties != NULL) {
          CFNumberRef widthNumberRef = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelWidth);
          if (widthNumberRef != NULL) {
              CFNumberGetValue(widthNumberRef, kCFNumberFloat64Type, &width);
          }
          CFNumberRef heightNumberRef = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelHeight);
          if (heightNumberRef != NULL) {
            CFNumberGetValue(heightNumberRef, kCFNumberFloat64Type, &height);
        }
        CFRelease(imageProperties);
    }
    CFRelease(imageSourceRef);
    }
    return CGSizeMake(width, height);
}