Question

Am facing thi really unusual problem with MKNetworkKit caching. In simple word’s the problem is that “It is not working”..!

I have created a simple test project which has the problem. The project does nothing, but just makes a simple GET request to http://where.yahooapis.com/ to fetch the the address or information for a city name. The response, is supposed to be chached the first time you run it and from second time the completion handler will be called twice, once with cached response and again with the fetched response. as you can see below, which is taken from http://blog.mugunthkumar.com/coding/ios-tutorial-image-cache-and-loading-thumbnails-using-mknetworkkit/

MKNetworkKit calls the SAME completion handler with cached data if you
are making the call for the second time. When the network connectivity
is proper, MKNetworkKit calls your completion handler twice. First
with the cached data and again after fetching the latest data from
server.

Well, the unusual thing is, I run the app, it didn’t cache, I again ran the app, it again didn’t cache, after some random runs suddenly the caching started working. I deleted the app and run it again, the cache wont work till some random runs and problem repeats..!

FYI, I have used the latest MKNetworkkit downloaded from GIT.

Am not sure whether it is some problem with my code, or a bug with MKNetworkKit itself. So please go through with the code, and let me know if its me or the MKNetworkKit that’s causing this problem.

Here is the link to download the sample project [https://www.box.com/s/tsfw3z0avpti051xbyhv]4

Thank, in advance.

Answer 1

Finally, I am able to figure it out..! So here is what happens , during caching,

MKNetworkKit caching is super light-weight and it caches your
responses in a NSMutableDictionary. Doesn’t that lead to high memory
usage? Yes. of-course, but MKNetworkKit is clever. It observes the
UIApplicationDidReceiveMemoryWarningNotification and flushes the
dictionary to disk. The next time you make a request to the cached
URL, the cached data is brought back to memory. So in-effect, it has a
in-memory cache and disk cache and uses a least recently used
algorithm to flush items to disk. The MKNetworkEngine class has
methods that can be over-ridden to control the cache cost.

So what was, happening is, that when I ran the app the first time, the response got cached in “memory” in and not in the “disk”. When I cold started the app, the response which was cached earlier was never transferred to “disk” from “memory”. (That was the reason why, there wasn’t even a cached file in in the application’s cache directory..!) Hence, the successBlock was never getting called twice, with a cached response, because, there wasn’t one..!

To get over this problem, its just overriding one function with just one line of code…!

- (int) cacheMemoryCost
{
    return 0;
}