图像未被缓存

Question

我正在以这种方式加载数据：

var request = NSURLRequest(URL: url!, cachePolicy: NSURLRequestCachePolicy.ReturnCacheDataElseLoad, timeoutInterval: Double.infinity);

if IJReachability.isConnectedToNetwork(){
 request = NSURLRequest(URL: url!, cachePolicy: NSURLRequestCachePolicy.UseProtocolCachePolicy, timeoutInterval: Double.infinity);
}

subtitleLabel.loadRequest(request);

它适用于我，包括缓存。唯一的问题是它不会缓存页面中的图像而且加载速度很慢..有没有办法缓存它们？

（我知道我还在使用旧的XCODE，但我还无法更新）

返回的HTML标头：

Array
(
    [Host] => ***.nl
    [Connection] => keep-alive
    [Cache-Control] => max-age=0
    [Accept] => text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
    [Upgrade-Insecure-Requests] => 1
    [User-Agent] => Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.93 Safari/537.36
    [Accept-Encoding] => gzip, deflate, sdch
    [Accept-Language] => en-US,en;q=0.8,hr;q=0.6,nl;q=0.4
    [Cookie] => PHPSESSID=dnvrv65pbvmrbfhi9kfskjb715
    [GEOIP_ADDR] => 84.25.56.128
    [GEOIP_CONTINENT_CODE] => EU
    [GEOIP_COUNTRY_CODE] => NL
    [GEOIP_COUNTRY_NAME] => Netherlands
    [Content-Length] => 0
)