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HttpRequestCacheLevel Enumeration

Note: This enumeration is new in the .NET Framework version 2.0.

Specifies caching behavior for resources obtained using the Hypertext Transfer protocol (HTTP).

Namespace: System.Net.Cache
Assembly: System (in system.dll)

public enum HttpRequestCacheLevel
public enum HttpRequestCacheLevel
public enum HttpRequestCacheLevel
 Member nameDescription
BypassCacheSatisfies a request by using the server. No entries are taken from caches, added to caches, or removed from caches between the client and server. 

This is the default cache behavior specified in the machine configuration file that ships with the .NET Framework.

CacheIfAvailableSatisfies a request for a resource from the cache if the resource is available; otherwise, sends a request for a resource to the server. If the requested item is available in any cache between the client and the server, the request might be satisfied by the intermediate cache. 
CacheOnlySatisfies a request using the locally cached resource; does not send a request for an item that is not in the cache. When this cache policy level is specified, a WebException exception is thrown if the item is not in the client cache. 
CacheOrNextCacheOnlySatisfies a request for a resource either from the local computer's cache or a remote cache on the local area network. If the request cannot be satisfied, a WebException exception is thrown. In the HTTP caching protocol, this is achieved using the only-if-cached cache control directive. 
DefaultSatisfies a request for a resource either by using the cached copy of the resource or by sending a request for the resource to the server. The action taken is determined by the current cache policy and the age of the content in the cache.  

This is the cache level that should be used by most applications.

NoCacheNoStoreNever satisfies a request by using resources from the cache and does not cache resources. If the resource is present in the local cache, it is removed. This policy level indicates to intermediate caches that they should remove the resource. In the HTTP caching protocol, this is achieved using the no-cache cache control directive. 
RefreshSatisfies a request by using the server or a cache other than the local cache. Before the request can be satisfied by an intermediate cache, that cache must revalidate its cached entry with the server. In the HTTP caching protocol, this is achieved using the max-age = 0 cache control directive and the no-cache Pragma header. 
ReloadSatisfies a request by using the server. The response might be saved in the cache. In the HTTP caching protocol, this is achieved using the no-cache cache control directive and the no-cache Pragma header. 
RevalidateCompares the copy of the resource in the cache with the copy on the server. If the copy on the server is newer, it is used to satisfy the request and replaces the copy in the cache. If the copy in the cache is the same as the server copy, the cached copy is used. In the HTTP caching protocol, this is achieved using a conditional request. 

This enumeration is used to set the cache level specified by HttpRequestCachePolicy objects.

The following code example sets the application domain's caching policy to Default.

// The following method demonstrates overriding the
// caching policy for a request.
public static WebResponse GetResponseNoCache(Uri uri)
{
    // Set a default policy level for the "http:" and "https" schemes.
    HttpRequestCachePolicy policy = new HttpRequestCachePolicy(HttpRequestCacheLevel.Default);
    HttpWebRequest.DefaultCachePolicy = policy;
    // Create the request.
    WebRequest request = WebRequest.Create(uri);
    // Define a cache policy for this request only. 
    HttpRequestCachePolicy noCachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.NoCacheNoStore);
    request.CachePolicy = noCachePolicy;
    WebResponse response = request.GetResponse();
    Console.WriteLine("IsFromCache? {0}", response.IsFromCache);            
    return response;
}

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0
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