HtmlSelect.OnPreRender(EventArgs) Método

Referencia

Definición

Espacio de nombres:: System.Web.UI.HtmlControls

Ensamblado:: System.Web.dll

Importante

Parte de la información hace referencia a la versión preliminar del producto, que puede haberse modificado sustancialmente antes de lanzar la versión definitiva. Microsoft no otorga ninguna garantía, explícita o implícita, con respecto a la información proporcionada aquí.

Genera el evento PreRender para el control HtmlSelect.

protected:
 override void OnPreRender(EventArgs ^ e);

protected public:
 override void OnPreRender(EventArgs ^ e);

protected override void OnPreRender (EventArgs e);

protected internal override void OnPreRender (EventArgs e);

override this.OnPreRender : EventArgs -> unit

Protected Overrides Sub OnPreRender (e As EventArgs)

Protected Friend Overrides Sub OnPreRender (e As EventArgs)

Parámetros

e: EventArgs

Objeto EventArgs que contiene los datos del evento.

Ejemplos

En el ejemplo de código siguiente se muestra cómo invalidar el OnPreRender método para que permita varias selecciones en un control de servidor personalizado HtmlSelect .

<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.CS.Controls" Assembly="Samples.AspNet.CS" %>
<%@ Page Language="C#" AutoEventWireup="True" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
    <head>
        <title>Custom HtmlSelect - OnPreRender - C# Example</title>
        <script runat="server">
      void HtmlInputButton1_ServerClick(Object sender, EventArgs e) 
      {
        if (HtmlSelect1.SelectedIndex >= 0)
        {
          if (HtmlSelect1.Multiple)
          {
            Div1.InnerHtml = "You selected:";
            for (int i=0; i<=HtmlSelect1.Items.Count - 1; i++)
            {
              if (HtmlSelect1.Items[i].Selected)
              {
                Div1.InnerHtml += "<br />    " + HtmlSelect1.Items[i].Value; 
              }     
            }
          }
          else
          {
            Div1.InnerHtml = "You selected " + HtmlSelect1.Value;
          }
        }
        else
        {
          Div1.InnerHtml = "You did not select an item.";
        }
      }
        </script>
    </head>
    <body>
        <form id="Form1" method="post" runat="server">
            <h3>Custom HtmlSelect - OnPreRender - C# Example</h3>
            
            <p>
      <aspSample:CustomHtmlSelectOnPreRender 
        id="HtmlSelect1" 
        name="HtmlSelect1"
        runat="server">
        <option value="Option1">Option1</option>
        <option value="Option2">Option2</option>
        <option value="Option3">Option3</option>
      </aspSample:CustomHtmlSelectOnPreRender>
      </p>
      
      <p>
      <input 
        id="HtmlInputButton1" 
        runat="server" 
        type="button" 
        onserverclick="HtmlInputButton1_ServerClick"
        value="Select" 
        name="HtmlInputButton1" />  
      </p>
      
      <br />
      <div id="Div1" runat="server" 
        style="DISPLAY: inline; WIDTH: 256px; HEIGHT: 15px" />
       
        </form>
    </body>
</html>

<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.VB.Controls" Assembly="Samples.AspNet.VB" %>
<%@ Page Language="VB" AutoEventWireup="True" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
    <head>
        <title>Custom HtmlSelect - OnPreRender - VB.NET Example</title>
        <script runat="server">
      Sub HtmlInputButton1_ServerClick(sender As Object, e As EventArgs)
        If HtmlSelect1.SelectedIndex >= 0 Then
            If HtmlSelect1.Multiple = True Then
              Div1.InnerHtml = "You selected:"
              Dim i As Integer
              For i = 0 To HtmlSelect1.Items.Count - 1
                  If HtmlSelect1.Items(i).Selected = True Then
                    Div1.InnerHtml += "<br />    " & HtmlSelect1.Items(i).Value
                  End If
              Next i
            Else
              Div1.InnerHtml = "You selected " & HtmlSelect1.Value
            End If
        Else
            Div1.InnerHtml = "You did not select an item."
        End If
      End Sub
        </script>
    </head>
    <body>
        <form id="Form1" method="post" runat="server">
            <h3>Custom HtmlSelect - OnPreRender - VB.NET Example</h3>
            
            <p>
      <aspSample:CustomHtmlSelectOnPreRender 
        id="HtmlSelect1" 
        name="HtmlSelect1"
        runat="server">
        <option value="Option1">Option1</option>
        <option value="Option2">Option2</option>
        <option value="Option3">Option3</option>
      </aspSample:CustomHtmlSelectOnPreRender>
      </p>
      
      <p>
      <input 
        id="HtmlInputButton1" 
        runat="server" 
        type="button" 
        onserverclick="HtmlInputButton1_ServerClick"
        value="Select" 
        name="HtmlInputButton1" />  
      </p>
      
      <br />
      <div id="Div1" runat="server" 
        style="DISPLAY: inline; WIDTH: 256px; HEIGHT: 15px" />
       
        </form>
    </body>
</html>

using System.Web;
using System.Security.Permissions;

namespace Samples.AspNet.CS.Controls
{
    [AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Minimal)]
    public sealed class CustomHtmlSelectOnPreRender : System.Web.UI.HtmlControls.HtmlSelect
    {
        protected override void OnPreRender(System.EventArgs e)
        {
            // Call the base's OnPreRender method.
            base.OnPreRender(e);
                
            // Allow multiple selections.
            this.Multiple = true;
        }
    }
}

<AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Minimal)> _
Public NotInheritable Class CustomHtmlSelectOnPreRender
    Inherits System.Web.UI.HtmlControls.HtmlSelect

    Protected Overrides Sub OnPreRender(ByVal e As System.EventArgs)

        ' Call the base's OnPreRender method.
        MyBase.OnPreRender(e)

        ' Allow multiple selections.
        Me.Multiple = True
    End Sub
End Class

Comentarios

Si la Size propiedad es mayor que 1, el OnPreRender método registra el HtmlSelect control con el Page control como uno que requiere procesamiento de postback.

Se aplica a

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