ASP.NET Clear Cache

Question

If you cache pages in a HttpHandler with

_context.Response.Cache.SetCacheability(HttpCacheability.Public);
_context.Response.Cache.SetExpires(DateTime.Now.AddSeconds(180));

is it possible to clear a certain page from the cache?

Answer 1

The following code will remove all keys from the cache:

public void ClearApplicationCache(){
    List<string> keys = new List<string>();
    // retrieve application Cache enumerator
    IDictionaryEnumerator enumerator = Cache.GetEnumerator();
    // copy all keys that currently exist in Cache
    while (enumerator.MoveNext()){
        keys.Add(enumerator.Key.ToString());
    }
    // delete every key from cache
    for (int i = 0; i < keys.Count; i++) {
        Cache.Remove(keys[i]);
    }
}

Modifying the second loop to check the value of the key before removing it should be trivial.

Hope this helps.

Answer 2

is it possible to Clear a certain page from the Cache?

Yes:

HttpResponse.RemoveOutputCacheItem("/pages/default.aspx");

You can also use Cache dependencies to remove pages from the Cache:

this.Response.AddCacheItemDependency("key");

After making that call, if you modify Cache["key"], it will cause the page to be removed from the Cache.

In case it might help, I cover caching in detail in my book: Ultra-Fast ASP.NET.