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WPF httpClient Cache deaktivieren

03.08.2018 (👁9808)

Folgendes Code Beispiel zeigt, wie man in WPF den Cache eines HttpClients deaktiviert.

Problem:

unter WPF und Winforms ist das abschalten des Caches in HttpClients und WebRequests immer wieder problematisch.

Dadurch werden URL Adressen trotz verschiedener Adress-Querystring Parametern immer gleich eingelesen.

Lösung:

Man kann den Windows 10 Core httpClient verwenden. In diesem httpClient wird der Cache stabil abgeschaltet.

Integrate the function under the program file:

To do this, you must now include the namespace of Windows 10 in the header

//< Windows 10 >

using Windows.Web.Http;

//</ Windows 10 >

Then you can use Windows 10 UWP methods

Here in the example a Window Core httpClient

(because deactivating the cache works here)

//--< Read HTML with httpClient >--

            //-< HttpClient >-

            HttpBaseProtocolFilter filter = new HttpBaseProtocolFilter();

            filter.CacheControl.ReadBehavior = HttpCacheReadBehavior.NoCache;

            filter.CacheControl.WriteBehavior = HttpCacheWriteBehavior.Default;

 

            Windows.Web.Http.HttpClient client = new Windows.Web.Http.HttpClient(filter);

            //-</ HttpClient >-

 

            //< read HTML >

            string sHTML = "";   //Client Request as string

            try

            {

                sHTML = await client.GetStringAsync(new Uri(sURL));                

            }

            catch (Exception ex)

            {

                //clsSys.show_Message(ex.Message);

                clsSys.fx_Log("Error httpClient: " + ex.Message);

                return null;

            }

            //</ read HTML >

            //--</ Read HTML with httpClient >--

 

 

 

 

Anhang: folgende klassische Cache-Anweisungen in WPF haben alle nicht funktioniert (Stand 2018)

//< HttpClient >

WebRequestHandler handler = new WebRequestHandler();

//*< not working >

//0:

//*handler.CachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.NoCacheNoStore); //.BypassCache);

//*</ not working >

handler.AllowAutoRedirect = false;

HttpClient httpClient = new HttpClient(handler);

//httpClient.DefaultRequestHeaders.Add("Cache-Control", "no-cache, no-store, must-revalidate");

//httpClient.DefaultRequestHeaders.Add("Cache-Control", "public");

//httpClient.DefaultRequestHeaders.Add("Cache-Control", "private");

 

//*< not working >

//1:

//*httpClient.DefaultRequestHeaders.Add("Cache-Control", "no-cache");

 

//2:

//*httpClient.DefaultRequestHeaders.CacheControl.NoStore = true;

 

//3:

//CacheControlHeaderValue cacheControl = new CacheControlHeaderValue();

//cacheControl.NoCache = true;

//httpClient.DefaultRequestHeaders.CacheControl = cacheControl;

 

//*</ not working >

 

 

string sHTML = "";   //Client Request as string

try

{

    sHTML = await httpClient.GetStringAsync(new Uri(sURL));

}

catch (Exception ex)

{

    //clsSys.show_Message(ex.Message);

    clsSys.fx_Log("Error httpClient: " + ex.Message);

    return null;

}

//</ HttpClient >

//-</ init >-

 

 

//< WebRequest and Response >

 

WebRequest objRequest = WebRequest.Create(sURL);

objRequest.CachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.NoCacheNoStore);

HttpWebResponse objResponse = (HttpWebResponse)objRequest.GetResponse();

//</ WebRequest and Response >

//< Stream and Reader >

Stream objDataStream = objResponse.GetResponseStream();

StreamReader TextReader = new StreamReader(objDataStream);

//</ Stream and Reader >