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HtmlSelect.OnPreRender Method

Raises the PreRender event for the HtmlSelect control.

Namespace:  System.Web.UI.HtmlControls
Assembly:  System.Web (in System.Web.dll)

protected internal override void OnPreRender(
	EventArgs e
)

Parameters

e
Type: System.EventArgs

An EventArgs that contains the event data.

If the Size property is greater than 1, then the OnPreRender method registers the HtmlSelect control with the Page control as one that requires postback processing.

The following code example demonstrates how to override the OnPreRender method so that it allows multiple selections in a custom HtmlSelect server control.

<%@ 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 == true)
          {
            Div1.InnerHtml = "You selected:";
            for (int i=0; i<=HtmlSelect1.Items.Count - 1; i++)
            {
              if (HtmlSelect1.Items[i].Selected == true)
              {
                Div1.InnerHtml += "<br /> &nbsp;&nbsp; " + 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" />&nbsp;&nbsp;
      </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;
        }
    }
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

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