WebRequest.CachePolicy 屬性

定義

命名空間:

System.Net

組件:

System.Net.Requests.dll

來源:

WebRequest.cs

取得或設定這個要求的快取原則。

public:
 virtual property System::Net::Cache::RequestCachePolicy ^ CachePolicy { System::Net::Cache::RequestCachePolicy ^ get(); void set(System::Net::Cache::RequestCachePolicy ^ value); };

public virtual System.Net.Cache.RequestCachePolicy? CachePolicy { get; set; }

member this.CachePolicy : System.Net.Cache.RequestCachePolicy with get, set

Public Overridable Property CachePolicy As RequestCachePolicy

屬性值

RequestCachePolicy

定義快取原則的 RequestCachePolicy 物件。

範例

下列程式代碼範例示範如何設定 Web 要求的快取原則。

// The following method demonstrates overriding the
// caching policy for a request.
static WebResponse^ GetResponseNoCache( Uri^ uri )
{
   // Set a default policy level for the "http:" and "https" schemes.
   HttpRequestCachePolicy^ policy = gcnew HttpRequestCachePolicy( HttpRequestCacheLevel::Default );
   HttpWebRequest::DefaultCachePolicy = policy;

   // Create the request.
   WebRequest^ request = WebRequest::Create( uri );

   // Define a cache policy for this request only. 
   HttpRequestCachePolicy^ noCachePolicy = gcnew HttpRequestCachePolicy( HttpRequestCacheLevel::NoCacheNoStore );
   request->CachePolicy = noCachePolicy;
   WebResponse^ response = request->GetResponse();
   Console::WriteLine( L"IsFromCache? {0}", response->IsFromCache );
   
   return response;
}

// 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;
}

備註

謹慎

WebRequest、HttpWebRequest、ServicePoint和 WebClient 已經過時，您不應該將它們用於新的開發。 請改用 HttpClient。

目前快取原則和快取中要求的資源是否存在，會判斷是否可以從快取擷取回應。 使用快取的回應通常可改善應用程式效能，但快取中的回應與伺服器上的回應不符的風險。

您可以在 Machine.config 組態檔中指定預設快取原則，或為使用超文本傳輸通訊協定 （HTTP） 或安全超文本傳輸通訊協定 （HTTPS） URI 配置的要求設定 DefaultCachePolicy 屬性。

只有在擷取資源響應數據流並讀取至數據流結尾時，才會將資源的複本新增至快取。 因此，相同資源的另一個要求可以使用快取的複本，視此要求的快取原則層級而定。

另請參閱

• RequestCachePolicy
• HttpRequestCacheLevel
• RequestCacheLevel
• DefaultCachePolicy
• DefaultCachePolicy