HttpWebRequest.BeginGetRequestStream Method (AsyncCallback, Object)
Begins an asynchronous request for a Stream object to use to write data.
Assembly: System (in System.dll)
<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)> Public Overrides Function BeginGetRequestStream ( callback As AsyncCallback, state As Object ) As IAsyncResult
The state object for this request.
The request cache validator indicated that the response for this request can be served from the cache; however, requests that write data must not use the cache. This exception can occur if you are using a custom cache validator that is incorrectly implemented.
Abort was previously called.
In a .NET Compact Framework application, a request stream with zero content length was not obtained and closed correctly. For more information about handling zero content length requests, see Network Programming in the .NET Compact Framework.
Themethod requires some synchronous setup tasks to complete (DNS resolution, proxy detection, and TCP socket connection, for example) before this method becomes asynchronous. As a result, this method should never be called on a user interface (UI) thread because it might take considerable time (up to several minutes depending on network settings) to complete the initial synchronous setup tasks before an exception for an error is thrown or the method succeeds.
To learn more about the thread pool, see The Managed Thread Pool.
Your application cannot mix synchronous and asynchronous methods for a particular request. If you call the BeginGetResponse method to retrieve the response.method, you must use the
This member outputs trace information when you enable network tracing in your application. For more information, see Network Tracing in the .NET Framework.
The following code example uses themethod to make an asynchronous request for a stream instance.
Imports System Imports System.Net Imports System.IO Imports System.Text Imports System.Threading Imports Microsoft.VisualBasic Class HttpWebRequestBeginGetRequest Public Shared allDone As New ManualResetEvent(False) Shared Sub Main() ' Create a new HttpWebRequest object. Dim request As HttpWebRequest = CType(WebRequest.Create("http://www.contoso.com/example.aspx"), _ HttpWebRequest) ' Set the ContentType property. request.ContentType = "application/x-www-form-urlencoded" ' Set the Method property to 'POST' to post data to the URI. request.Method = "POST" ' Start the asynchronous operation. Dim result As IAsyncResult = _ CType(request.BeginGetRequestStream(AddressOf GetRequestStreamCallback, request), _ IAsyncResult) ' Keep the main thread from continuing while the asynchronous ' operation completes. A real world application ' could do something useful such as updating its user interface. allDone.WaitOne() End Sub ' Main Private Shared Sub GetRequestStreamCallback(ByVal asynchronousResult As IAsyncResult) Dim request As HttpWebRequest = CType(asynchronousResult.AsyncState, HttpWebRequest) ' End the operation Dim postStream As Stream = request.EndGetRequestStream(asynchronousResult) Console.WriteLine("Please enter the input data to be posted:") Dim postData As [String] = Console.ReadLine() ' Convert the string into byte array. Dim byteArray As Byte() = Encoding.UTF8.GetBytes(postData) ' Write to the stream. postStream.Write(byteArray, 0, postData.Length) postStream.Close() ' Start the asynchronous operation to get the response Dim result As IAsyncResult = _ CType(request.BeginGetResponse(AddressOf GetResponseCallback, request), _ IAsyncResult) End Sub ' ReadRequestStreamCallback Private Shared Sub GetResponseCallback(ByVal asynchronousResult As IAsyncResult) Dim request As HttpWebRequest = CType(asynchronousResult.AsyncState, HttpWebRequest) ' Get the response. Dim response As HttpWebResponse = CType(request.EndGetResponse(asynchronousResult), _ HttpWebResponse) Dim streamResponse As Stream = response.GetResponseStream() Dim streamRead As New StreamReader(streamResponse) Dim responseString As String = streamRead.ReadToEnd() Console.WriteLine(responseString) ' Close Stream object. streamResponse.Close() streamRead.Close() ' Release the HttpWebResponse. allDone.Set() response.Close() End Sub ' ReadResponseCallback End Class ' HttpWebRequest_BeginGetRequest
Available since 8
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Available since 8.1