HttpListener.BeginGetContext(AsyncCallback, Object) 方法

  • 参考

定义

命名空间:
System.Net
程序集:
System.Net.HttpListener.dll
程序集:
System.dll
程序集:
netstandard.dll
Source:
HttpListener.Managed.cs
Source:
HttpListener.Managed.cs
Source:
HttpListener.Managed.cs

开始异步检索传入的请求。

public:
 IAsyncResult ^ BeginGetContext(AsyncCallback ^ callback, System::Object ^ state);
public IAsyncResult BeginGetContext (AsyncCallback? callback, object? state);
public IAsyncResult BeginGetContext (AsyncCallback callback, object state);
member this.BeginGetContext : AsyncCallback * obj -> IAsyncResult
Public Function BeginGetContext (callback As AsyncCallback, state As Object) As IAsyncResult

参数

callback
AsyncCallback

AsyncCallback 委托，引用客户端请求可用时要调用的方法。

state
Object

一个用户定义对象，其中包含操作的相关信息。 操作完成时，此对象传递给 callback 委托。

返回

IAsyncResult

一个指示异步操作状态的 IAsyncResult 对象。

例外

HttpListenerException

Win32 函数调用失败。 检查异常的 ErrorCode 属性以确定导致异常的原因。

InvalidOperationException

此对象尚未启动或当前已停止。

ObjectDisposedException

此对象已关闭。

示例

下面的代码示例演示如何使用 BeginGetContext 方法来指定将处理传入客户端请求的回调方法。


public static void NonblockingListener(string [] prefixes)
{
    HttpListener listener = new HttpListener();
    foreach (string s in prefixes)
    {
        listener.Prefixes.Add(s);
    }
    listener.Start();
    IAsyncResult result = listener.BeginGetContext(new AsyncCallback(ListenerCallback),listener);
    // Applications can do some work here while waiting for the
    // request. If no work can be done until you have processed a request,
    // use a wait handle to prevent this thread from terminating
    // while the asynchronous operation completes.
    Console.WriteLine("Waiting for request to be processed asyncronously.");
    result.AsyncWaitHandle.WaitOne();
    Console.WriteLine("Request processed asyncronously.");
    listener.Close();
}

Public Shared Sub NonblockingListener(ByVal prefixes As String())
    Dim listener As HttpListener = New HttpListener()

    For Each s As String In prefixes
        listener.Prefixes.Add(s)
    Next

    listener.Start()
    Dim result As IAsyncResult = listener.BeginGetContext(New AsyncCallback(AddressOf ListenerCallback), listener)
    ' Applications can do some work here while waiting for the 
    ' request. If no work can be done until you have processed a request,
    ' use a wait handle to prevent this thread from terminating
    ' while the asynchronous operation completes.
    Console.WriteLine("Waiting for request to be processed asyncronously.")
    result.AsyncWaitHandle.WaitOne()
    Console.WriteLine("Request processed asyncronously.")
    listener.Close()
End Sub

下面的代码示例实现回调方法。

public static void ListenerCallback(IAsyncResult result)
{
    HttpListener listener = (HttpListener) result.AsyncState;
    // Call EndGetContext to complete the asynchronous operation.
    HttpListenerContext context = listener.EndGetContext(result);
    HttpListenerRequest request = context.Request;
    // Obtain a response object.
    HttpListenerResponse response = context.Response;
    // Construct a response.
    string responseString = "<HTML><BODY> Hello world!</BODY></HTML>";
    byte[] buffer = System.Text.Encoding.UTF8.GetBytes(responseString);
    // Get a response stream and write the response to it.
    response.ContentLength64 = buffer.Length;
    System.IO.Stream output = response.OutputStream;
    output.Write(buffer,0,buffer.Length);
    // You must close the output stream.
    output.Close();
}

Public Shared Sub ListenerCallback(ByVal result As IAsyncResult)
    Dim listener As HttpListener = CType(result.AsyncState, HttpListener)
    ' Call EndGetContext to complete the asynchronous operation.
    Dim context As HttpListenerContext = listener.EndGetContext(result)
    Dim request As HttpListenerRequest = context.Request
    ' Obtain a response object.
    Dim response As HttpListenerResponse = context.Response
    ' Construct a response.
    Dim responseString As String = "<HTML><BODY> Hello world!</BODY></HTML>"
    Dim buffer As Byte() = System.Text.Encoding.UTF8.GetBytes(responseString)
    ' Get a response stream and write the response to it.
    response.ContentLength64 = buffer.Length
    Dim output As System.IO.Stream = response.OutputStream
    output.Write(buffer, 0, buffer.Length)
    ' You must close the output stream.
    output.Close()
End Sub

注解

方法 BeginGetContext 开始异步 (非阻塞) 调用以接收传入的客户端请求。 在调用此方法之前，必须调用 Start 方法，并将至少一个统一资源标识符 (URI 添加) 前缀来侦听，方法是将 URI 字符串添加到 HttpListenerPrefixCollection 属性返回的 Prefixes 。

异步操作必须通过调用 EndGetContext 方法来完成。 通常，委托会调用 callback 方法。

此方法不会在操作完成时阻止。 若要获取传入请求并阻止操作完成，请 GetContext 调用 方法。

有关使用异步编程模型的详细信息，请参阅 异步调用同步方法。

调用方说明

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。 有关详细信息，请参阅.NET Framework中的网络跟踪。

适用于