HtmlInputFile.OnPreRender(EventArgs) Method

Reference

Definition

Namespace:: System.Web.UI.HtmlControls

Assembly:: System.Web.dll

Important

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Raises the PreRender event for the HtmlInputFile control.

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)

Parameters

e: EventArgs

An EventArgs that contains event data.

Examples

The following code example demonstrates how to override the OnPreRender method so that a Title attribute is always added to each custom HtmlInputFile control. For this example to work properly, you need to create a directory called Temp on your computer's drive C.

<%@ 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">
<script runat="server">

  void Button1_Click(object Source, EventArgs e)
  {
    // Make sure a file was submitted.
    if (HtmlInputText1.Value == "")
    {
      
      Span1.InnerHtml = "Error: You must enter a file name.";
      
    }
      
    // Save the file.
    else if (HtmlInputFile1.PostedFile != null)
    {  
      try
      {
        
        HtmlInputFile1.PostedFile.SaveAs("c:\\temp\\" + HtmlInputText1.Value);
        Span1.InnerHtml = "File uploaded successfully to: <b>c:\\temp\\" + 
                           HtmlInputText1.Value + "</b> on the Web server.";
               
      }
      catch (Exception exc)
      {
        
        Span1.InnerHtml = "Error saving <b>c:\\temp\\" +
                           HtmlInputText1.Value + "</b><br />" + exc.ToString() + ".";
        
      }
      
    }
    
  }
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
  <head>
    <title>Custom HtmlInputFile OnPreRender Example</title>
  </head>
  <body>
    <form id="form1" enctype="multipart/form-data"
          runat="server">

      <h3>Custom HtmlInputFile OnPreRender Example</h3>
 
      Select File to Upload:
      <aspSample:CustomHtmlInputFileOnPreRender
        id="HtmlInputFile1"
        type="file"
        runat="server"
        name="HtmlInputFile1">

      <p>
      Save as file name (no path):
      <input id="HtmlInputText1"
        type="text"
        runat="server"
        name="Text1" />

      </p>
      <p>
      <span id="Span1"
        style="font: 8pt verdana;"
        runat="server" />

      </p>
      <p>
      <input type="button"
        id="Button1"
        value="Upload"
        onserverclick="Button1_Click"
        runat="server"
        name="Button1" />

      </p>

    </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">
<script runat="server">
  
  Sub Button1_Click(ByVal source As Object, ByVal e As EventArgs)

    ' Make sure the file was submitted.  
    If HtmlInputText1.Value = "" Then
      
      Span1.InnerHtml = "Error: You must enter a file name."
    
    ' Save the file 
    ElseIf Not (HtmlInputFile1.PostedFile Is Nothing) Then

      Try
        
        HtmlInputFile1.PostedFile.SaveAs("c:\\temp\\" & HtmlInputText1.Value)
        Span1.InnerHtml = "File uploaded successfully to: <b>c:\temp\" _
                        & HtmlInputText1.Value & "</b> on the Web server."

      Catch exc As Exception
        
        Span1.InnerHtml = "Error saving <b>c:\temp\" _
                        & HtmlInputText1.Value & "</b><br />" _
                        & exc.ToString() & "."
        
      End Try
      
    End If
    
  End Sub
  
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
  <head>
    <title>Custom HtmlInputFile OnPreRender Example</title>
  </head>

  <body>
    <form id="form1" enctype="multipart/form-data"
          runat="server">

      <h3>Custom HtmlInputFile OnPreRender Example</h3>

      Select File to Upload:
      <aspSample:CustomHtmlInputFileOnPreRender
        id="HtmlInputFile1"
        type="file"
        runat="server"
        name="HtmlInputFile1">

      <p>
      Save as file name (no path):
      <input id="HtmlInputText1"
        type="text"
        runat="server"
        name="Text1" />

      </p>
      <p>
      <span id="Span1"
        style="font: 8pt verdana;"
        runat="server" />

      </p>
      <p>
      <input type="button"
        id="Button1"
        value="Upload"
        onserverclick="Button1_Click"
        runat="server"
        name="Button1" />

      </p>

    </form>

  </body>
</html>

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

namespace Samples.AspNet.CS.Controls
{
    [AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Minimal)]
    public sealed class CustomHtmlInputFileOnPreRender : System.Web.UI.HtmlControls.HtmlInputFile
    {
        protected override void OnPreRender(System.EventArgs e)
        {
            // Call the base OnPreRender method.
            base.OnPreRender(e);
            
            // Add a Title attribute to the HtmlInputFile control.
            this.Attributes.Add("title", "Click the Browse button to select a file to upload.");
        }
    }
}

Imports System.Web
Imports System.Security.Permissions

Namespace Samples.AspNet.VB.Controls

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

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

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

            ' Add a Title attribute to the HtmlInputFile control.
            Me.Attributes.Add("title", "Click the Browse button to select a file to upload.")
        End Sub
    End Class

End Namespace

Remarks

If no encoding is specified for the Web page's HtmlForm control, the Enctype property is set to "multipart/form-data".

Applies to

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