BeginEventHandler Delegato

Definizione

Rappresenta il metodo che consente di gestire gli eventi asincroni, quali gli eventi dell'applicazione.Represents the method that handles asynchronous events such as application events. Questo delegato viene chiamato all'avvio di un'operazione asincrona.This delegate is called at the start of an asynchronous operation.

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 

Parametri

sender
Object

Origine dell'evento.The source of the event.

e
EventArgs

Oggetto EventArgs che contiene i dati dell'evento.An EventArgs that contains the event data.

cb
AsyncCallback

Delegato da chiamare una volta completata la chiamata al metodo asincrona.The delegate to call when the asynchronous method call is complete. Se cb è null, il delegato non viene chiamato.If cb is null, the delegate is not called.

extraData
Object

Eventuali dati aggiuntivi necessari per l'elaborazione della richiesta.Any additional data needed to process the request.

Valore restituito

IAsyncResult

Elemento IAsyncResult che rappresenta il risultato dell'operazione BeginEventHandler.The IAsyncResult that represents the result of the BeginEventHandler operation.

Ereditarietà
BeginEventHandler

Esempi

Nell'esempio di codice seguente viene BeginEventHandler usato il delegato per registrare un gestore di una pagina asincrona.The following code example uses the BeginEventHandler delegate to register a handler an asynchronous page.

Importante

L'esempio include una casella di testo che accetta l'input dell'utente e rappresenta quindi una potenziale minaccia alla sicurezza.This example has a text box that accepts user input, which is a potential security threat. Per impostazione predefinita, le pagine Web ASP.NET verificano che l'input dell'utente non includa script o elementi HTML.By default, ASP.NET Web pages validate that user input does not include script or HTML elements. Per altre informazioni, vedere Cenni preliminari sugli attacchi tramite script.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>
<%@ 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>

Commenti

Quando si crea un delegato BeginEventHandler, si identifica il metodo che gestirà l'evento.When you create a BeginEventHandler delegate, you identify the method that will handle the event. Per associare l'evento al gestore eventi in uso, aggiungere all'evento un'istanza del delegato.To associate the event with your event handler, add an instance of the delegate to the event. Il gestore eventi viene chiamato ogni volta che si verifica l'evento, a meno che non venga rimosso il delegato.The event handler is called whenever the event occurs, unless you remove the delegate. Per ulteriori informazioni sui delegati del gestore eventi, vedere gestione e generazione di eventi.For more information about event-handler delegates, see Handling and Raising Events.

Metodi di estensione

GetMethodInfo(Delegate)

Ottiene un oggetto che rappresenta il metodo rappresentato dal delegato specificato.Gets an object that represents the method represented by the specified delegate.

Si applica a

Vedi anche