通过

BeginEventHandler 委托

  • 参考

定义

命名空间:
System.Web
程序集:
System.Web.dll

表示处理异步事件（如应用程序事件）的方法。 此委托在异步操作开始时调用。

public delegate IAsyncResult ^ BeginEventHandler(System::Object ^ sender, EventArgs ^ e, AsyncCallback ^ cb, System::Object ^ extraData);
public delegate IAsyncResult BeginEventHandler(object sender, EventArgs e, AsyncCallback cb, object extraData);
type BeginEventHandler = delegate of obj * EventArgs * AsyncCallback * obj -> IAsyncResult
Public Delegate Function BeginEventHandler(sender As Object, e As EventArgs, cb As AsyncCallback, extraData As Object) As IAsyncResult

参数

sender
Object

事件源。

e
EventArgs

包含事件数据的 EventArgs。

cb
AsyncCallback

异步方法调用完成时要调用的委托。 如果 cb 为 null，则不调用委托。

extraData
Object

处理请求所需的任何其他数据。

返回值

IAsyncResult

IAsyncResult，它表示 BeginEventHandler 操作的结果。

示例

下面的代码示例使用 BeginEventHandler 委托注册处理程序异步页。

重要

此示例具有一个接受用户输入的文本框，这是一个潜在的安全威胁。 默认情况下，ASP.NET 网页验证用户输入是否不包含脚本或 HTML 元素。 有关详细信息，请参阅脚本侵入概述。

<%@ page language="C#" Async="true"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
  System.Net.WebRequest myRequest;

  void Page_Load(object sender, EventArgs e)
  {
    Label1.Text = "Page_Load: thread #" + System.Threading.Thread.CurrentThread.GetHashCode();

    BeginEventHandler bh = new BeginEventHandler(this.BeginGetAsyncData);
    EndEventHandler eh = new EndEventHandler(this.EndGetAsyncData);

    AddOnPreRenderCompleteAsync(bh, eh);

    // Initialize the WebRequest.
    string address = "http://localhost/";

    myRequest = System.Net.WebRequest.Create(address);
  }

  IAsyncResult BeginGetAsyncData(Object src, EventArgs args, AsyncCallback cb, Object state)
  {
    Label2.Text = "BeginGetAsyncData: thread #" + System.Threading.Thread.CurrentThread.GetHashCode();
    return myRequest.BeginGetResponse(cb, state);
  }

  void EndGetAsyncData(IAsyncResult ar)
  {
    Label3.Text = "EndGetAsyncData: thread #" + System.Threading.Thread.CurrentThread.GetHashCode();

    System.Net.WebResponse myResponse = myRequest.EndGetResponse(ar);

    result.Text = new System.IO.StreamReader(myResponse.GetResponseStream()).ReadToEnd();
    myResponse.Close();
  }

</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
  <head runat="server">
    <title>
      Page.AddOnPreRenderCompleteAsync Example</title>
  </head>
  <body>
    <form id="form1" runat="server">
      <asp:label id="Label1" runat="server">
        Label 1</asp:label><br />
      <asp:label id="Label2" runat="server">
        Label 2</asp:label><br />
      <asp:label id="Label3" runat="server">
        Label 3</asp:label><br />
      <asp:textbox id="result" runat="server" textMode="multiLine" ReadOnly="true" columns="80" rows="25" />
    </form>
  </body>
</html>

<%@ page language="VB" Async="true"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
  Dim myRequest As System.Net.WebRequest
  
  Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
    Label1.Text = "Page_Load: Thread #" & System.Threading.Thread.CurrentThread.GetHashCode()
    
    Dim bh As New BeginEventHandler(AddressOf Me.BeginGetAsyncData)
    Dim eh As New EndEventHandler(AddressOf Me.EndGetAsyncData)
    
    Me.AddOnPreRenderCompleteAsync(bh, eh)
    
    ' Initialize the WebRequest object.
    Dim address As String
    address = "http://localhost/"
    myRequest = System.Net.WebRequest.Create(address)
    
  End Sub
  
  Function BeginGetAsyncData(ByVal src As Object, ByVal args As EventArgs, ByVal cb As AsyncCallback, ByVal state As Object) As IAsyncResult
    Label2.Text = "BeginGetAsyncData: Thread #" & System.Threading.Thread.CurrentThread.GetHashCode()
    Return Me.myRequest.BeginGetResponse(cb, state)
  End Function
  
  Sub EndGetAsyncData(ByVal ar As IAsyncResult)
    Label3.Text = "EndGetAsyncData: Thread #" & System.Threading.Thread.CurrentThread.GetHashCode()
    
    Dim myResponse As System.Net.WebResponse
    myResponse = Me.myRequest.EndGetResponse(ar)
    
    Dim reader As New System.IO.StreamReader(myResponse.GetResponseStream())
    result.Text = reader.ReadToEnd()
    myResponse.Close()
  End Sub
  
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
  <head runat="server">
    <title>
      Page.AddOnPreRenderCompleteAsync Example</title>
  </head>
  <body>
    <form id="form1" runat="server">
      <asp:label id="Label1" runat="server">
        Label 1</asp:label><br />
      <asp:label id="Label2" runat="server">
        Label 2</asp:label><br />
      <asp:label id="Label3" runat="server">
        Label 3</asp:label><br />
      <asp:textbox id="result" runat="server" textMode="multiLine" ReadOnly="true" columns="80" rows="25" />
    </form>
  </body>
</html>

注解

创建 BeginEventHandler 委托时，需要标识将处理该事件的方法。 若要将事件与事件处理程序关联，请将该委托的一个实例添加到事件中。 除非移除了该委托，否则每当发生该事件时就会调用事件处理程序。 有关事件处理程序委托的详细信息，请参阅 处理和引发事件。

扩展方法

GetMethodInfo(Delegate)

获取指示指定委托表示的方法的对象。

适用于

另请参阅