SDWebImage 获取缓存的文件名

NSData *imageData = nil;
    BOOL isExit = [[SDWebImageManager sharedManager] diskImageExistsForURL:[NSURL URLWithString:imageURL]];
    if (isExit) {
        NSString *cacheImageKey = [[SDWebImageManager sharedManager] cacheKeyForURL:[NSURL URLWithString:imageURL]];
        if (cacheImageKey.length) {
            NSString *cacheImagePath = [[SDImageCache sharedImageCache] defaultCachePathForKey:cacheImageKey];
            if (cacheImagePath.length) {
                imageData = [NSData dataWithContentsOfFile:cacheImagePath];
            }
        }
    }
    if (!imageData) {
       imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:imageURL]];
    }
    return imageData;