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how to display random images on an ASP document?

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Description

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.

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).

Code

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<%
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

'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
%>