Hello
Could anyone please explain how I can pass more than one
arguement/parameter value to a function using <asp:linkbutton> or is
this a major shortfall of the language ?
Consider the following code fragments in which I want to list through
all files on a directory with a link to download each file by passing
a filename and whether or not to force the download dialog box to
appear.
Codebehind
public void DownloadFile(string fname,bool forceDownload)
{
.....
.....
}
<script language="C#" runat="server">
void CommandBtn_Click(Object sender, CommandEventArgs e)
{
DownloadFile(e.CommandArgument,???);
}
</script>
<asp:linkbutton id="LinkButton2"
style="Z-INDEX: 101; LEFT: 136px; POSITION: absolute; TOP: 200px"
OnCommand="CommandBtn_Click" runat="server"
CommandArgument="test.doc" Width="240px" Height="48px"
CommandName="FileName">LinkButton</asp:linkbutton>
"major shortfall" is probably a bit strong; an “inconvenience” maybe.
You have several options at your disposal:
OPTION1: use different CommandNames, e.g.:
<asp:linkbutton id="LinkButton1" OnCommand="CommandBtn_Click" CommandName="DownloadFile" CommandArgument="test1.doc" …
LinkButton1</asp:linkbutton>
<asp:linkbutton id="LinkButton2" OnCommand="CommandBtn_Click" CommandName="DownloadForce" CommandArgument="test2.doc" …
LinkButton2</asp:linkbutton>
public void DownloadFile(string fname,bool forceDownload) {
.....
}
void CommandBtn_Click(object sender, CommandEventArgs e) {
bool forceDownload =
(e.CommandName == “DownloadForce”) ? true : false;
DownloadFile((string)e.CommandArgument, forceDownload );
}
OPTION2: use different CommandEventHandlers, e.g.:
<asp:linkbutton id="LinkButton1" OnCommand="CommandBtn_Click" CommandName="FileName" CommandArgument="test1.doc" …
LinkButton1</asp:linkbutton>
<asp:linkbutton id="LinkButton2" OnCommand="CommandForceBtn_Click" CommandName="FileName" CommandArgument="test2.doc" …
LinkButton2</asp:linkbutton>
public void DownloadFile(string fname,bool forceDownload) {
.....
}
void CommandBtn_Click(object sender, CommandEventArgs e) {
DownloadFile((string)e.CommandArgument, false );
}
void CommandForceBtn_Click(object sender, CommandEventArgs e) {
DownloadFile((string)e.CommandArgument, true );
}
OPTION3: You can stuff your arguments into that single CommandArgument. It can be as simple as a delimited string or as complex as
an XML document. This is most suitable if you create the LinkButtons dynamically. Example:
<!-- DynamicButtons.aspx -->
<%@ Page language="c#" Codebehind="DynamicButtons.aspx.cs" AutoEventWireup="false" Inherits="LbtnArg.DynamicButtons" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
<HTML>
<HEAD>
<title>DynamicButtons</title>
<meta content="Microsoft Visual Studio .NET 7.1" name="GENERATOR">
<meta content="C#" name="CODE_LANGUAGE">
<meta content="JavaScript" name="vs_defaultClientScript">
<meta content="
http://schemas.microsoft.com/intellisense/ie5" name="vs_targetSchema">
</HEAD>
<body>
<form id="Form1" method="post" runat="server">
<asp
anel id="pnlLinks" runat="server" Height="312px" Width="528px"></asp
anel></form>
</body>
</HTML>
// DynamicButtons.aspx.cs
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.IO;
using System.Text.RegularExpressions;
using System.Xml;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
namespace LbtnArg {
public class DynamicButtons : System.Web.UI.Page {
protected System.Web.UI.WebControls.Panel pnlLinks;
// Page_Load dynamically adds LinkButtons to the panel
// for each xml, txt, html, zip file in the specified directory
// and prepares the command arguments
private void Page_Load(object sender, System.EventArgs e){
// Attributes of directories or filed we do not want
const FileAttributes excludeMask =
FileAttributes.Directory
| FileAttributes.Hidden
| FileAttributes.Temporary
| FileAttributes.System
| FileAttributes.Encrypted;
// Types of file we want to show
Regex includeTypes = new Regex(
@"^\.(xml)|(html)|(txt)|(zip)$",
RegexOptions.IgnoreCase
);
// Get all the items in the directory
DirectoryInfo di = new DirectoryInfo(".");
FileSystemInfo[] fsi = di.GetFileSystemInfos();
foreach( FileSystemInfo info in fsi ){
// Don't list directories or files with
// undesirable attributes
if( (info.Attributes & excludeMask) != 0)
continue;
// Only list specific types
if( ! includeTypes.IsMatch(info.Extension) )
continue;
// Add the link button for the file
LinkButton linkButton = new LinkButton();
linkButton.Text = info.Name;
if( info.Extension.ToLower() == ".zip" ){
linkButton.Command += new CommandEventHandler( DownloadDialog );
linkButton.CommandName = "DOWNLOADDIALOG";
} else {
linkButton.Command += new CommandEventHandler( DownloadSimple );
linkButton.CommandName = "DOWNLOADSIMPLE";
}
linkButton.CommandArgument = ArgToString( info );
pnlLinks.Controls.Add( linkButton );
// add a <br>
HtmlControl lcBreak = new HtmlGenericControl("br");
pnlLinks.Controls.Add( lcBreak );
} // end foreach item in the directory
} // end EventHandler DynamicButtons.Page_Load
// Both CommandEventHandlers delegate the actual
// work the DownloadFile method.
// CommandEventHandler which hardcodes the bool
// parameter to "true"
protected void DownloadSimple(
object sender,
CommandEventArgs e
){
// Call DownloadFile
// hardcoding the bool parameter to "true"
DownloadFile(
e.CommandName,
(string)e.CommandArgument,
true
);
} // End CommandEventHandler DynamicButtons.DownloadSimple
// CommandEventHandler which hardcodes the bool
// parameter to "false"
protected void DownloadDialog(
object sender,
CommandEventArgs e
){
// Call DownloadFile
// hardcoding the bool parameter to "false"
DownloadFile(
e.CommandName,
(string)e.CommandArgument,
false
);
} // End CommandEventHandler DynamicButtons.DownloadDialog
// Names for elements in the argument string
private const string groupElemNm_ = "data";
private const string nameElemNm_ = "name";
private const string fullNameElemNm_ = "fullName";
private const string extensionElemNm_ = "extension";
// Stuff the arguments into an XML fragment
private string ArgToString( FileSystemInfo info ){
StringWriter sw = new StringWriter();
XmlTextWriter xw = new XmlTextWriter( sw );
xw.WriteStartElement( groupElemNm_ );
xw.WriteElementString( nameElemNm_, info.Name );
xw.WriteElementString( fullNameElemNm_, info.FullName );
xw.WriteElementString( extensionElemNm_,info.Extension );
xw.WriteEndElement();
xw.Flush();
string argString = sw.ToString();
xw.Close();
return argString;
} // End DynamicButtons.ArgToString
// Helper method for StringToArg
private string GetElementValue( XmlTextReader reader ){
reader.Read();
return reader.NodeType == XmlNodeType.Text ? reader.Value : string.Empty;
} // End DynamicButtons.GetElementValue
// Extract the arguments from the XML fragment
private void StringToArg(
string argStr,
ref string name,
ref string fullName,
ref string extension
){
bool readElements = false;
StringReader sr = new StringReader( argStr );
XmlTextReader xr = new XmlTextReader( sr );
xr.WhitespaceHandling = WhitespaceHandling.None;
// Get past the enclosing element
while( xr.Read() ) {
if( xr.NodeType == XmlNodeType.Element ) {
readElements = (xr.Name == groupElemNm_ );
break;
}
}
// Now process the contained elements
if( readElements ){
while( xr.Read() ){
if( xr.NodeType != XmlNodeType.Element )
continue;
if ( xr.Name == nameElemNm_ )
name = GetElementValue( xr );
else if ( xr.Name == fullNameElemNm_ )
fullName = GetElementValue( xr );
else if ( xr.Name == extensionElemNm_ )
extension = GetElementValue( xr );
} // end while more elements
} // end if enclosing "data" element
xr.Close();
} // End DynamicButtons.StringToArg
// Helper method for "DownloadFile"
private void AddTableRow( Table tbl, string desc, string valueStr ){
TableRow row = new TableRow();
TableCell tcDesc = new TableCell();
TableCell tcValue = new TableCell();
tcDesc.Text= desc;
tcValue.Text = valueStr;
row.Cells.Add( tcDesc );
row.Cells.Add( tcValue );
tbl.Rows.Add( row );
} // End DynamicButtons.AddTableRow
// Simply demonstrate handling of the arguments and display
private void DownloadFile(
string cmdName,
string cmdArg,
bool forceDownload
){
string fileName = string.Empty;
string fileFullName = string.Empty;
string fileExtension = string.Empty;
StringToArg( cmdArg, ref fileName, ref fileFullName, ref fileExtension );
// Display the Results
Table tbl = new Table();
tbl.GridLines = GridLines.Both;
tbl.BorderStyle = BorderStyle.Solid;
AddTableRow( tbl, "forceDownload", forceDownload.ToString() );
AddTableRow( tbl, "Command Name", cmdName );
AddTableRow( tbl, nameElemNm_, fileName );
AddTableRow( tbl, fullNameElemNm_, fileFullName );
AddTableRow( tbl, extensionElemNm_, fileExtension );
pnlLinks.Controls.Add( tbl );
} // End DynamicButtons.Downloadfile
#region Web Form Designer generated code
override protected void OnInit(EventArgs e)
{
//
// CODEGEN: This call is required by the ASP.NET Web Form Designer.
//
InitializeComponent();
base.OnInit(e);
}
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.Load += new System.EventHandler(this.Page_Load);
}
#endregion
}
}
