How do I invalidate iOS's cache for a particular URL?

Question

Using NSURLSession\'s default caching, how do I invalidate the cache for a particular URL?

I note NSURLCache\'s removeCachedResponseF

Answer 1

The solution turns out not to be invalidating the cache for an existing URL, but to set:

request.cachePolicy = NSURLRequestReloadIgnoringLocalCacheData;

When you make the next request for the resource you know to be invalid. There are options to ignore the local cache only, or to request that upstream proxies ignore their caches too. See the NSURLRequest/NSMutableURLRequest documentation for details.

Answer 2

If you want to go further you could reset the cached response for the url request you want to force the reload. Doing the following:

let newResponse = NSHTTPURLResponse(URL: urlrequest.URL!, statusCode: 200, HTTPVersion: "1.1", headerFields: ["Cache-Control":"max-age=0"])
let cachedResponse = NSCachedURLResponse(response: newResponse!, data: NSData())
NSURLCache.sharedURLCache().storeCachedResponse(cachedResponse, forRequest: urlrequest)

As the cache-control header of the response hax a max age of 0 (forced) the response will never be returned when you do this request.

Your answer works fine for forcing a single request, but if you want to have two versions of the request one forcing and another relying on the cached response, removing the cached one once you force a request is desired.

Answer 3

Here's what has been working for me:

request.cachePolicy = NSURLRequestCachePolicy.ReloadIgnoringCacheData

Here are all the options listed regarding chache policy, so you may find one that better suits your need:

Using Swift 2.2 and Xcode 7.3