下面的代码示例使用 BeginGetRequestStream 方法对流实例发出异步请求。

       private void ppkie()
        {
            int time1, time2;
            time1 = Environment.TickCount;

            textBox1.Text = "";
            label1.Text = "";
            // Create a new HttpWebRequest object.
            HttpWebRequest request = (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.    
            request.BeginGetRequestStream(new AsyncCallback(RequestCallBack), 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();

            // Get the response.
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            Stream streamResponse = response.GetResponseStream();
            StreamReader streamRead = new StreamReader(streamResponse);
            string responseString = streamRead.ReadToEnd();
            //Console.WriteLine(responseString);
            this.textBox1.Text = responseString;
            // Close the stream object.
            streamResponse.Close();
            streamRead.Close();

            // Release the HttpWebResponse.
            response.Close();

            time2 = Environment.TickCount - time1;
            label1.Text = time2.ToString();
        }


        private static void RequestCallBack(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 = "Please enter the input data to be posted:";

            // Convert the string into a byte array.
            byte[] byteArray = new byte[256]; 
            // Write to the request stream.
            postStream.Write(byteArray, 0, postData.Length);
            postStream.Close();
            allDone.Set();
        }