WebRequest.BeginGetRequestStream(AsyncCallback, Object) 方法

定义

命名空间:

System.Net

程序集:

netstandard.dll, System.Net.Requests.dll

Source:

WebRequest.cs

在后代类中重写时，提供 GetRequestStream() 方法的异步版本。

C#

public virtual IAsyncResult BeginGetRequestStream(AsyncCallback? callback, object? state);

参数

callback

AsyncCallback

AsyncCallback 委托。

state

Object

包含此异步请求的状态信息的对象。

返回

IAsyncResult

引用异步请求的 IAsyncResult。

例外

NotImplementedException

在子代类中未重写该方法时，将尝试访问该方法。

示例

以下示例使用 BeginGetRequestStream 异步获取请求流。

C#

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

public class RequestState
{
    // This class stores the request state of the request.
    public WebRequest request;    
    public RequestState()
    {
        request = null;
    }
}

class WebRequest_BeginGetRequeststream
{
    public static ManualResetEvent allDone= new ManualResetEvent(false);
    static void Main()
    {
            // Create a new request to the mentioned URL.
            WebRequest myWebRequest= WebRequest.Create("http://www.contoso.com");

            // Create an instance of the RequestState and assign 
            // 'myWebRequest' to it's request field.
            RequestState myRequestState = new RequestState();
            myRequestState.request = myWebRequest;
            myWebRequest.ContentType="application/x-www-form-urlencoded";

            // Set the 'Method' property to 'POST' to post data to a Uri.
            myRequestState.request.Method="POST";
            // Start the Asynchronous 'BeginGetRequestStream' method call.
            IAsyncResult r=(IAsyncResult) myWebRequest.BeginGetRequestStream(
                new AsyncCallback(ReadCallback),myRequestState);
            // Pause the current thread until the async operation completes.
            Console.WriteLine("main thread waiting...");
            allDone.WaitOne();
            // Assign the response object of 'WebRequest' to a 'WebResponse' variable.
            WebResponse myWebResponse = myWebRequest.GetResponse();
            Console.WriteLine("The string has been posted.");
            Console.WriteLine("Please wait for the response...");

            Stream streamResponse = myWebResponse.GetResponseStream();
            StreamReader streamRead = new StreamReader( streamResponse );
            Char[] readBuff = new Char[256];
            int count = streamRead.Read( readBuff, 0, 256 );
            Console.WriteLine("\nThe contents of the HTML page are ");

            while (count > 0) 
            {
                String outputData = new String(readBuff, 0, count);
                Console.Write(outputData);
                count = streamRead.Read(readBuff, 0, 256);
            }

            // Close the Stream Object.
            streamResponse.Close();
            streamRead.Close();

            // Release the HttpWebResponse Resource.
            myWebResponse.Close();
    }
    private static void ReadCallback(IAsyncResult asynchronousResult)
    {
            RequestState myRequestState =(RequestState) asynchronousResult.AsyncState;
            WebRequest myWebRequest = myRequestState.request;

            // End the Asynchronous request.
            Stream streamResponse = myWebRequest.EndGetRequestStream(asynchronousResult);

            // Create a string that is to be posted to the uri.
            Console.WriteLine("Please enter a string to be posted:");
            string postData = Console.ReadLine();
            // Convert the string into a byte array.
            byte[] byteArray = Encoding.UTF8.GetBytes(postData);

            // Write the data to the stream.
            streamResponse.Write(byteArray,0,postData.Length);
            streamResponse.Close();
            allDone.Set();
    }
}

注解

注意

WebRequest、HttpWebRequest、ServicePoint和 WebClient 已过时，不应将其用于新开发。 请改用 HttpClient。

BeginGetRequestStream 方法为用于将数据发送到 Internet 资源的流启动异步请求。 实现 AsyncCallback 委托的回调方法使用 EndGetRequestStream 方法返回请求流。

备注

WebRequest 类是 abstract 类。 运行时 WebRequest 实例的实际行为由 WebRequest.Create 方法返回的后代类确定。 有关默认值和异常的详细信息，请参阅子代类的文档，例如 HttpWebRequest 和 FileWebRequest。

适用于

另请参阅

• EndGetRequestStream(IAsyncResult)
• 发出异步请求