ASP Kitchen: ASPWatch.com articles: Random Image Selector

Random Image Selector

Introduction

Here is a small function that allows random images to be displayed on an ASP document. Although this is an easy task to achieve in ASP, or even using client-side JavaScript, the VBScript function shown here has the advantage of not needing to know the number of images within the folder – it will take account of images being to added or removed from the images folder. An example random image is shown below. Refresh this page to see another:

The RandomImage function is shown below:

<%
Function RandomImage(ImagesFolderPath, ImageFileTypes, ImageDescription)

'Declare variables
Dim CompleteImagesFolderPath
Dim FileSystemObject
Dim ImageFolder
Dim Files
Dim i
Dim ImageFiles
Dim File
Dim FileName
Dim FileExtension
Dim RandomNumber

'Find the complete path to image folder by using Server.MapPath
CompleteImagesFolderPath = Server.MapPath(ImagesFolderPath)

'Create an instance of the FileSystemObject which allows ASP to
'access the file system 
Set FileSystemObject = Server.CreateObject("Scripting.FileSystemObject")

'Check that the folder containing the images exists
If Not FileSystemObject.FolderExists(CompleteImagesFolderPath) Then
RandomImage = "Error 0: Cannot find requested folder"
Set FileSystemObject = nothing
Exit Function
End If

'Get the folder containing the images
Set ImageFolder = FileSystemObject.GetFolder(CompleteImagesFolderPath)

'Get a list of all the files within the images folder
Set Files = ImageFolder.Files

'Use a dictionary object to temporarily store the image file names
i = 1
Set ImageFiles = Server.CreateObject("Scripting.Dictionary")

'Loop through the list of files within the images folder.
'If the file has a file extension that is in the list of
'file types specified in the ImageFileTypes function parameter,
'then add the file name to the ImageFiles dictionary object
For Each File in Files

FileName = File.Name
FileExtension = Right(FileName, Len(FileName) - (InStrRev(FileName, ".")))

If InStr(1,ImageFileTypes,FileExtension,vbTextCompare) > 0 then
ImageFiles.Add i, FileName
i = i + 1
End If

Next

'Destroy objects that are no longer required
Set ImageFolder = nothing
Set Files = nothing
Set FileSystemObject = nothing

'Initialise the random number generator
Randomize

' Check that image file(s) have been found
If ImageFiles.Count = 0 Then
RandomImage = "Error 1: Requested folder does not contain any image files"
Exit Function
End If

'Generate a random number between 1 and the number of image files
RandomNumber = Int((ImageFiles.Count) * Rnd + 1)

'Return a hyperlink to a random image file
RandomImage = "<img src=" & Chr(34) & ImagesFolderPath & ImageFiles.Item(RandomNumber) & Chr(34) & " alt=" & Chr(34) & ImageDescription & Chr(34) & ">"

Set ImageFiles = nothing

End Function
%>


The function uses the FileSystemObject object to access the file system. It checks that the specified image folder exists, and then extracts a list of files within the folder. A link to one of the images (chosen at random) is then returned.

There is a certain amount of error checking within the script; it will return an error message if it cannot find the images folder, and also if it cannot find any appropriate image files.

The function can be called using the following VBScript:

<%Response.Write RandomImage("images/", "gif jpeg", "My Image")%>

The function has three arguments. The first (ImagesFolderPath) is the name of the folder containing the images, and it should be a sub-folder of the folder that contains the ASP document. The second argument should be a string containing a list of file types to use as images (e.g. jpeg, jpg, gif). Finally, the last argument is a short sentence to describe your image (which is used as the image’s ALT tag).

Further reading

• Sams Teach Yourself Web Development With ASP in 24 Hours. Start learning ASP with this introductory guide.

• A JavaScript Banner Ad Rotator. Displays a different image after a specific amount of time. Each image is linked to a different URL.

Useful Development Tools

ASP Documentation Tool™

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.NET Documentation Tool

Automatically creates technical documentation for .NET Framework applications written in C# or VB.NET (including ASP.NET). Documentation for SQL Server 7/2000/2005 databases and C#/VB.NET components associated with the web application can also be incorporated into the reports. Documentation is created in HTML, HTML Help and plain text formats. Additional support for ASP.NET web applications. A useful alternative to NDoc!

View Sample Output (HTML Help format).     View Sample Output (HTML Format).     Download Trial Version (3Mb ZIP file).

SQL Documentation Tool

The SQL Documentation Tool creates technical documentation for Microsoft SQL Server 7.0, 2000 and 2005 databases. Technical documentation is created in HTML and HTML Help formats. The HTML Help format documentation is fully searchable and cross referenced. The SQL Documentation Tool documents SQL Server Tables, Views, Stored Procedures, Triggers, Table Relationships, Jobs and DTS Packages.

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VB Documentation Tool

The VB Documentation Tool creates technical documentation for Microsoft Visual Basic 6.0 projects. Technical documentation is created in HTML and HTML Help formats. The HTML Help format documentation is fully searchable and cross referenced.

View Sample Output (HTML Help format).     View Sample Output (HTML Format).     Download Trial Version (1Mb ZIP file).

The Website Utility

The Website Utility examines websites for errors and areas that need to be optimised for search engines by using a built in web crawling engine. Errors checked for include broken or moved hyperlinks, missing page titles and missing meta tags. It also generates HTML for use in creating website site maps (table of contents pages - like this one), and is able to create both client-side JavaScript search engines and server-side ASP search engines and ASP.NET search engines for a website.

View Sample Output (HTML Format).     Download Trial Version (3Mb ZIP file).

Text Workbench

Text Workbench is a file search and replacement utility for text files and Microsoft Office documents. Make rapid file replacements on multiple files and folders full of files. Advanced replacement options include regular expressions support. It even works on remote file systems via FTP. A Regular Expression Laboratory allows advanced pattern matching and replacement expressions to be built and tested. This great utility will make your everyday development tasks much easier!

Download Trial Version (3Mb ZIP file; you have the option to either install directly from this link or save the file for later installation).

Indexing Service Companion

The Indexing Service Companion is a utility that extends the functionality of the Microsoft Windows Indexing Service so that it is able to index content from any remote website and also from ODBC compliant databases. As such it can be used as a low cost alternative to Sharepoint's Search Services.

View Product Documentation (119K ZIP file).     Try Sample Search Facility.     Download Trial Version (1.7Mb ZIP file).

ASP Spell Check

ASPSpellCheck is the easy way to add spell checking capabilities to your ASP or ASP.NET websites, Intranets and web applications. The utility allows you to add spell checking capabilities to any HTML text field or rich content editing text box. It works with all common web browsers, and there are no components or databases to install on the server.

Read ASPSpellCheck Review.     View ASPSpellCheck Examples.     Download Trial Version (3Mb ZIP file; you have the option to either install directly from this link or save the file for later installation).

Author details

Brett Burridge has worked as a web developer since 1997 and has developed web applications for a range of corporations, start up busiensses and educational establishments.

Brett is presently employed as an Internet developer and technical writer through his own company, Winnersh Triangle Web Solutions Limited. The company produces a number of innovative products, including a range of software documentation tools, which include the ASP Documentation Tool™, the .NET Documentation Tool for VB.NET and C#, and the SQL Server Documentation Tool. Other products include The Website Utility, which functions as a website error checker, search engine optimizer and ASP/ASP.NET search engine builder application.

As well as the ASPAlliance, Brett has written articles for Ariadne.ac.uk, ASPToday, the software documentation portal www.softwaredocumentation.info, and has contributed recipes to the ASP.NET Developer's Cookbook.    links

Outside web development, Brett is interested in travelling (here are my travel logs from New York, Hong Kong and Tokyo), digital photography (here's my photo gallery), tropical fishkeeping and collecting contemporary works of art by artists such as Doug Hyde.

Contact Brett by emailing

Article history

"Random image selector" originally published on ASPWatch.com on June 8 2000. Republished on ASPAlliance.com on 26 September 2001.

ASP Kitchen: ASPWatch.com articles: Random Image Selector