用SDWebImage下载后再刷新这种方式吧~

新建 UIImage分类

#import <ImageIO/ImageIO.h>

+ (CGSize)yf_imageSizeWithURL:(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);
        //以下是对手机32位、64位的处理
        if (imageProperties != NULL) {
            CFNumberRef widthNumberRef = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelWidth);
#if defined(__LP64__) && __LP64__
            if (widthNumberRef != NULL) {
                CFNumberGetValue(widthNumberRef, kCFNumberFloat64Type, &width);
            }
            CFNumberRef heightNumberRef = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelHeight);
            if (heightNumberRef != NULL) {
                CFNumberGetValue(heightNumberRef, kCFNumberFloat64Type, &height);
            }
#else
            if (widthNumberRef != NULL) {
                CFNumberGetValue(widthNumberRef, kCFNumberFloat32Type, &width);
            }
            CFNumberRef heightNumberRef = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelHeight);
            if (heightNumberRef != NULL) {
                CFNumberGetValue(heightNumberRef, kCFNumberFloat32Type, &height);
            }
#endif
            CFRelease(imageProperties);
        }
        
        CFRelease(imageSourceRef);
    }
    return CGSizeMake(width, height);
}