HttpWebRequest.BeginGetRequestStream(AsyncCallback, Object) 方法
定义
重要
一些信息与预发行产品相关，相应产品在发行之前可能会进行重大修改。 对于此处提供的信息，Microsoft 不作任何明示或暗示的担保。
开始 Stream 对象用于写入数据的异步请求。
public:
override IAsyncResult ^ BeginGetRequestStream(AsyncCallback ^ callback, System::Object ^ state);public override IAsyncResult BeginGetRequestStream (AsyncCallback callback, object state);public override IAsyncResult BeginGetRequestStream (AsyncCallback? callback, object? state);override this.BeginGetRequestStream : AsyncCallback * obj -> IAsyncResultPublic Overrides Function BeginGetRequestStream (callback As AsyncCallback, state As Object) As IAsyncResult参数
- callback
- AsyncCallback
AsyncCallback 委托。
- state
- Object
此请求的状态对象。
返回
引用异步请求的 IAsyncResult。
例外
Method 属性为 GET 或 HEAD。
-或-
KeepAlive
true，AllowWriteStreamBuffering 为 false，ContentLength 为 -1，SendChunked 为 false，Method 为 POST 或 PUT。
上一次调用 BeginGetRequestStream(AsyncCallback, Object) 正在使用流
-或-
TransferEncoding 设置为值，SendChunkedfalse。
-或-
线程池已耗尽线程。
请求缓存验证程序指示可从缓存中提供此请求的响应;但是，写入数据的请求不得使用缓存。 如果使用未正确实现的自定义缓存验证程序，则可能会出现此异常。
以前调用 Abort()。
在 .NET Compact Framework 应用程序中，未正确获取和关闭长度为零的请求流。 有关处理零内容长度请求的详细信息，请参阅 .NET Compact Framework中的
示例
下面的代码示例使用 BeginGetRequestStream 方法为流实例发出异步请求。
#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
谨慎
WebRequest、HttpWebRequest、ServicePoint和 WebClient 已过时，不应将其用于新开发。 请改用 HttpClient。
BeginGetRequestStream 方法启动用于发送 HttpWebRequest数据的流的异步请求。 异步回调方法使用 EndGetRequestStream 方法返回实际流。
BeginGetRequestStream 方法要求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），然后此方法才变为异步。 因此，不应在用户界面（UI）线程上调用此方法，因为它可能需要相当长的时间（最多几分钟，具体取决于网络设置）才能完成初始同步设置任务，然后引发错误异常或方法成功。
若要详细了解线程池，请参阅 托管线程池。
注意
应用程序无法混合特定请求的同步和异步方法。 如果调用 BeginGetRequestStream 方法，则必须使用 BeginGetResponse 方法来检索响应。
注意
在应用程序中启用网络跟踪时，此成员将输出跟踪信息。 有关详细信息，请参阅 .NET Framework中的
