HttpWebRequest.BeginGetRequestStream(AsyncCallback, Object) 方法

定义

开始对用于写入数据的 Stream 对象执行异步请求。Begins an asynchronous request for a Stream object to use to write data.

public:
 override IAsyncResult ^ BeginGetRequestStream(AsyncCallback ^ callback, System::Object ^ state);
public override IAsyncResult BeginGetRequestStream (AsyncCallback callback, object state);
override this.BeginGetRequestStream : AsyncCallback * obj -> IAsyncResult
Public Overrides Function BeginGetRequestStream (callback As AsyncCallback, state As Object) As IAsyncResult

参数

callback
AsyncCallback

AsyncCallback 委托。The AsyncCallback delegate.

state
Object

此请求的状态对象。The state object for this request.

返回

引用该异步请求的 IAsyncResultAn IAsyncResult that references the asynchronous request.

异常

Method 属性为 GET 或 HEAD。The Method property is GET or HEAD.

-or- KeepAlivetrueAllowWriteStreamBufferingfalseContentLength 为 -1,SendChunkedfalseMethod 为 POST 或 PUT。KeepAlive is true, AllowWriteStreamBuffering is false, ContentLength is -1, SendChunked is false, and Method is POST or PUT.

BeginGetRequestStream(AsyncCallback, Object) 的前一次调用正在使用流The stream is being used by a previous call to BeginGetRequestStream(AsyncCallback, Object)

-or- TransferEncoding 设置为一个值,且 SendChunkedfalseTransferEncoding is set to a value and SendChunked is false.

-or- 线程池中线程即将耗尽。The thread pool is running out of threads.

请求缓存验证程序指示对此请求的响应可从缓存中提供;但是,写入数据的请求不得使用缓存。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. 如果你正在使用错误实现的自定义缓存验证程序,则会发生此异常。This exception can occur if you are using a custom cache validator that is incorrectly implemented.

之前已调用 Abort()Abort() was previously called.

在 .NET Compact Framework 应用程序中,未正确获得和关闭一个内容长度为零的请求流。In a .NET Compact Framework application, a request stream with zero content length was not obtained and closed correctly. 有关处理内容长度为零的请求的详细信息,请参阅 .NET Compact Framework 中的网络编程For more information about handling zero content length requests, see Network Programming in the .NET Compact Framework.

示例

下面的代码示例使用 BeginGetRequestStream 方法发出对流实例的异步请求。The following code example uses the BeginGetRequestStream method to make an asynchronous request for a stream instance.

#using <System.dll>

using namespace System;
using namespace System::Net;
using namespace System::IO;
using namespace System::Text;
using namespace System::Threading;
ref class HttpWebRequestBeginGetRequest
{
public:
   static ManualResetEvent^ allDone = gcnew ManualResetEvent( false );
   static void Main()
   {
      
      // Create a new HttpWebRequest object.
      HttpWebRequest^ request = dynamic_cast<HttpWebRequest^>(WebRequest::Create( "http://www.contoso.com/example.aspx" ));
      
      // 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.    
      AsyncCallback^ del = gcnew AsyncCallback(GetRequestStreamCallback);
      request->BeginGetRequestStream( del, request );
      
      // 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();
    }
      

private:
    static void GetRequestStreamCallback(IAsyncResult^ asynchronousResult)
    {
        HttpWebRequest^ request = dynamic_cast<HttpWebRequest^>(asynchronousResult->AsyncState);
        
        // End the operation
        Stream^ postStream = request->EndGetRequestStream(asynchronousResult);

        Console::WriteLine("Please enter the input data to be posted:");
        String^ postData = Console::ReadLine();

        // Convert the string into a byte array.
        array<Byte>^ByteArray = Encoding::UTF8->GetBytes(postData);

        // Write to the request stream.
        postStream->Write(ByteArray, 0, postData->Length);
        postStream->Close();

        // Start the asynchronous operation to get the response
        AsyncCallback^ del = gcnew AsyncCallback(GetResponseCallback);
        request->BeginGetResponse(del, request);
    }

   static void GetResponseCallback(IAsyncResult^ asynchronousResult)
   {
      HttpWebRequest^ request = dynamic_cast<HttpWebRequest^>(asynchronousResult->AsyncState);

      // End the operation
      HttpWebResponse^ response = dynamic_cast<HttpWebResponse^>(request->EndGetResponse(asynchronousResult));
      Stream^ streamResponse = response->GetResponseStream();
      StreamReader^ streamRead = gcnew StreamReader(streamResponse);
      String^ responseString = streamRead->ReadToEnd();
      Console::WriteLine(responseString);
      // Close the stream object
      streamResponse->Close();
      streamRead->Close();

      // Release the HttpWebResponse
      response->Close();
      allDone->Set();
   }
};

void main()
{
   HttpWebRequestBeginGetRequest::Main();
}

using System;
using System.Net;
using System.IO;
using System.Text;
using System.Threading;

class HttpWebRequestBeginGetRequest
{
    private static ManualResetEvent allDone = new ManualResetEvent(false);

    public static void Main(string[] args)
    {


        // Create a new HttpWebRequest object.
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.contoso.com/example.aspx");

        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
        request.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback), request);

        // 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();
    }

    private static void GetRequestStreamCallback(IAsyncResult asynchronousResult)
    {
        HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
        
        // End the operation
        Stream postStream = request.EndGetRequestStream(asynchronousResult);

        Console.WriteLine("Please enter the input data to be posted:");
        string postData = Console.ReadLine();

        // Convert the string into a byte array.
        byte[] byteArray = Encoding.UTF8.GetBytes(postData);

        // Write to the request stream.
        postStream.Write(byteArray, 0, postData.Length);
        postStream.Close();

        // Start the asynchronous operation to get the response
        request.BeginGetResponse(new AsyncCallback(GetResponseCallback), request);
    }

    private static void GetResponseCallback(IAsyncResult asynchronousResult)
    {
        HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;

        // End the operation
        HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
        Stream streamResponse = response.GetResponseStream();
        StreamReader streamRead = new StreamReader(streamResponse);
        string responseString = streamRead.ReadToEnd();
        Console.WriteLine(responseString);
        // Close the stream object
        streamResponse.Close();
        streamRead.Close();

        // Release the HttpWebResponse
        response.Close();
        allDone.Set();
    }
}
Imports System.Net
Imports System.IO
Imports System.Text
Imports System.Threading

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

    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

    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
            
End Class

注解

BeginGetRequestStream 方法将启动一个用于发送 HttpWebRequest的数据的流的异步请求。The BeginGetRequestStream method starts an asynchronous request for a stream used to send data for the HttpWebRequest. 异步回调方法使用 EndGetRequestStream 方法返回实际流。The asynchronous callback method uses the EndGetRequestStream method to return the actual stream.

在此方法成为异步之前,BeginGetRequestStream 方法需要完成一些同步安装任务(例如,DNS 解析、代理检测和 TCP 套接字连接)。The BeginGetRequestStream method requires some synchronous setup tasks to complete (DNS resolution, proxy detection, and TCP socket connection, for example) before this method becomes asynchronous. 因此,永远不应在用户界面(UI)线程上调用此方法,因为它可能需要很长时间(取决于网络设置),以便在引发错误之前完成初始同步设置任务或方法成功。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.

若要了解有关线程池的详细信息,请参阅托管线程池To learn more about the thread pool, see The managed thread pool.

备注

应用程序不能为特定请求混合使用同步和异步方法。Your application cannot mix synchronous and asynchronous methods for a particular request. 如果调用 BeginGetRequestStream 方法,则必须使用 BeginGetResponse 方法来检索响应。If you call the BeginGetRequestStream method, you must use the BeginGetResponse method to retrieve the response.

备注

当你在应用程序中启用网络跟踪后,此成员将输出跟踪信息。This member outputs trace information when you enable network tracing in your application. 有关详细信息,请参阅.NET Framework 中的网络跟踪For more information, see Network Tracing in the .NET Framework.

适用于

另请参阅