Open Multiple Files on Multiple Windows from Code behind in ASP.NET using C# and VB.NET

In this article, we will learn how to dynamically open multiple files in separate popup browser windows in ASP.NET. Since the files are stored on the server, a server-side script is required to retrieve them. To open the popup windows on the client side, we will use JavaScript and the window.open() function.

Open multiple window from code behind

The client script (JavaScript) will be generated and registered at the server side simultaneously while fetching the files from a folder.

Fetching Files from Server Folder and Opening Them in Popup Windows

Using the ASP.NET System.IO namespace, we will fetch the files from a folder on the server. Once the files are retrieved, we will loop through the list and register each file with JavaScript using the ASP.NET ClientScript.RegisterStartupScript method, allowing each file to open in a separate popup window.

The ClientScript.RegisterStartupScript method takes four parameters to register the startup script. The first parameter is the type of the startup script. The second parameter is a string value for the key of the script. The third parameter is the script (or the function you wrote the script). The forth parameter is addScriptTags, Boolean (true or false) indicating whether to add script tags.

Page.ClientScript.RegisterStartupScript(this.GetType, "Popup_File", "window.open();", true);

Ref: ClientScriptManager.RegisterStartupScript Method

Overview

The main highlight of the above script is type this.GetType (Me.GetType in VB.NET) and the key value Popup_File. We must always add a unique type and key combination for all the registered scripts on a single page. Since each script will be uniquely identified using this combination. Therefore, we will add a File Counter with the KEY to keep it unique.

C#

"Popup_File" + iFileCnt;

VB.NET

"Popup_File" & iFileCnt

Note: You can also use ASP.NET “GUID” instead of a counter, to generate unique ID’s.

C#

"Popup_File" + Guid.NewGuid();

VB.NET

"Popup_File" & Guid.NewGuid()

window.open() function

The open() method will open a new browser window.

Syntax:

window.open (url, name, specifications, replace (boolean))

• url – The url or the location of the web page which is to be opened.
• name – The target attribute of the page. E.g. _blank.
• specifications – Define the necessary features of the newly created or opened window. Like, should it have a toolbar, the address bar or should the window be sizeable etc.
• replace – True if the new location will replace the current page in the history list.

Now let us see how we can open multiple files in multiple browser windows using all the above mentioned features.

Please Note: Your browser may not allow windows to popup by default, so you need to explicitly set the browser accordingly to allow the windows to popup.

HTML

We just need a button to do a post back to the server to fetch the files and then popup on new windows.

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html>
<html>
<head>
    <title>Open or Popup Multiple Browser Windows</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <input type="button" runat="server" 
            onserverclick="ShowWindow" value="Show Files" />
    </div>
    </form>
</body>
</html>

Code Behind (C#)

using System;
using System.IO;

public partial class _Default : System.Web.UI.Page 
{
    protected void ShowWindow(object sender, EventArgs e)
    {
        // THE FOLDER PATH WHERE WE HAVE THE FILES.
        DirectoryInfo objDir = new DirectoryInfo(Server.MapPath("Files"));      
        FileInfo[] objFI = objDir.GetFiles("*.pdf");        // LOOK FOR PDF's ONLY.

        int iFileCnt = 0;       // COUNTER TO CREATE UNIQUE KEYS FOR EACH SCRIPT.

        if (objFI.Length > 0){
            foreach (FileInfo file in objFI)
            {
                // REGISTER AND OPEN A NEW WINDOW.
                Page.ClientScript.RegisterStartupScript(this.GetType(), "Popup_File" + iFileCnt,
                    "window.open('https://localhost:555/csharp/files/" + objFI[iFileCnt].Name + "','_blank');", true);

                iFileCnt += 1;
            }
        }
    }
}

VB.NET

Option Explicit On
Imports System.IO

Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub ShowWindow(ByVal sender As Object, ByVal e As EventArgs)

        Dim objDir As New DirectoryInfo(Server.MapPath("Files"))      ' THE FOLDER PATH WHERE WE HAVE THE FILES.
        Dim objFI As FileInfo() = objDir.GetFiles("*.pdf")        ' LOOK FOR PDF's ONLY.

        Dim iFileCnt As Integer = 0     ' COUNTER TO CREATE UNIQUE KEYS FOR EACH SCRIPT.

        If objFI.Length > 0 Then
            For Each file As FileInfo In objFI

                ' REGISTER AND OPEN A NEW WINDOW.
                Page.ClientScript.RegisterStartupScript(Me.GetType, "Popup_File" & iFileCnt, _
                    "window.open('https://localhost:555/vb/files/" & objFI(iFileCnt).Name & "','_blank');", True)

                iFileCnt = iFileCnt + 1
            Next
        End If
    End Sub
End Class

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