BeginEventHandler Delegate
Represents the method that handles asynchronous events such as application events. This delegate is called at the start of an asynchronous operation.
Namespace: System.Web
Assembly: System.Web (in System.Web.dll)
public delegate IAsyncResult BeginEventHandler( Object sender, EventArgs e, AsyncCallback cb, Object extraData )
Parameters
- sender
- Type: System.Object
The source of the event.
- e
- Type: System.EventArgs
An EventArgs that contains the event data.
- cb
- Type: System.AsyncCallback
The delegate to call when the asynchronous method call is complete. If cb is null, the delegate is not called.
- extraData
- Type: System.Object
Any additional data needed to process the request.
Return Value
Type: System.IAsyncResultThe IAsyncResult that represents the result of the BeginEventHandler operation.
When you create a BeginEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about event-handler delegates, see Events and Delegates.
The following code example uses the BeginEventHandler delegate to register a handler an asynchronous page.
 Security Note |
|---|
This example has a text box that accepts user input, which is a potential security threat. By default, ASP.NET Web pages validate that user input does not include script or HTML elements. For more information, see Script Exploits Overview. |
<%@ 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>
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
