Attempting to globally cache data in a C# WebService but having issues

I am working with an API that runs pretty slowly, and as a result my application is taking a pretty big performance hit. I have managed to optimize some of the code and cut down the loading time considerably, but I would also like to cache some data across all sessions to minimize the amount of server hits I have to make. There is one API call I make now that takes almost 10 seconds to run, and the data returned rarely changes (maybe once every few weeks). What I would like to do is cache that result, as well as the time it was retrieved, and only make the API call if a certain amount of time has passed since the last call, otherwise returning the cached results. Currently I am attempting this:

[WebMethod]
    public List<RegionLis开发者_Go百科t> getRegionLists() {
        if (GlobalAppCache.RegionListsLastUpdate == DateTime.MinValue || GlobalAppCache.RegionListsLastUpdate.AddMinutes(15) > DateTime.Now)
        {
            List<RegionList> regionLists = new List<RegionList>( );
            // Do Some API Calls
            GlobalAppCache.RegionListsLastUpdate = DateTime.Now;
            GlobalAppCache.CachedRegionLists = regionLists;
            return regionLists;
        }
        return GlobalAppCache.CachedRegionLists;
    }

With the GlobalAppCache class being:

public class GlobalAppCache {
    public static DateTime RegionListsLastUpdate{get;set;}
    public static List<RegionList> CachedRegionLists{get;set;}
}

This method of caching doesn't appear to be working (The API Call is made every time, and the cached results are never returned), and I haven't been able to get anything having to do with the Application[] array to work either. Could anyone point me in the right direction? If I can get this working I may be able to improve performance by caching more items in this GlobalAppCache object. Thanks!

Try writing to the HttpApplicationState object Application. When retrieving the Data you should pay attention to the casting to correct datatype:

Application["LastUpdate"] = DateTime.Now;

.. .. ..

object o = Application["LastUpdate"];
if (o != null) DateTime dLastUpdate = Convert.ToDateTime(o);

... ...

The Application object dies when the AppPool the webservice runs in gets restarted / recycled

Ok, I have found a solution for my issue. Apparently while reading the documentation for the WebMethod flag, I missed the CacheDuration property. Since I was trying to cache the output of my methods, simply changing

[WebMethod]

to

[WebMethod(CacheDuration = (60*60*24*2))]

fixed it!