Adding Methods to Custom Class Objects in VBScript
In my last article I began showing you how to create your own custom class objects in VBScript. We started building the CompressedFolder class, a class that allows you to create and manipulate compressed folders natively. This article will expand on what you learned.
We started by creating a class and adding various properties to it, but having a few properties doesn’t do much for this class. We also need a way to create the compressed folder and to add to and remove files from it. For that we need to add some methods. These are the functions and subroutines that perform the magic when the class is called.
Just like Properties, these methods can be either Public or Private. Again, the Public methods will be exposed to scripts through the class object. The structure of methods is identical to that of functions and subroutines used outside of a class, with the simple exception that we’ll be providing either a private or public declaration.
Public Sub Create(strFile)
If objFso.FileExists(strFile) Then objFso.DeleteFile(strFile)
Here I’ve added two methods to my class. The Open() method is a Public method that can be used by the class object in my scripts. When I pass a parameter to this method, the class will internally call the private NewCompressedFolder() method.
I could have easily housed all of the code in the NewCompressedFolder method within the Open method and eliminated the need for it. I don’t like to do that. I prefer to keep all of the internal workings of a class within its own private methods. This is a pretty common practice for most programmers.
As you can see, methods inside of a class are no different from the functions and subroutines you write in your scripts every day. Here’s the full list of methods used by the CompressedFolder class.
Public Sub Open(strFile)
FullName = strFile
End Sub
Public Sub Create(strFile)
If objFso.FileExists(strFile) Then objFso.DeleteFile(strFile)
'You must provide an applicable sleep routine for use in ASP.
WScript.Sleep intDuration
End Sub
Take the time to see which ones are Private and which are Public. Do you see how they relate to each other? I’m using the exposed (Public) methods to call the internal (Private) methods. For a further explanation of the inner workings of these functions, stayed tuned for my Understanding the CompressedFolder class series.
All of the basic pieces for the CompressedFolder class are now in place. We’ve provided all of the properties and methods along with their required code. In VBScript there is no way to create your own custom events for your classes. However, there are two intrinsic events that you can use, and I want to demonstrate how to handle those.
VBScript classes have Initialize and Terminate events. The first fires when the class is instantiated, and the latter fires when that object is released. These are handled in a typical VBS fashion using the object-underscore naming convention. In this case, we can simply use the Class keyword for the event handle.
Private Sub Class_Initialize
Set objShell = CreateObject("Shell.Application")
Set objFso = CreateObject("Scripting.FileSystemObject")
End Sub
Private Sub Class_Terminate
Set objShell = Nothing
Set objFso = Nothing
End Sub
The Class_Initialize subroutine will be executed when the Initialize event occurs. This happens when the programmer creates a reference to this class and instantiates its object. This provides a nice opportunity for us to connect to any objects that will be used globally in our class. Since we want these to be made available globally, we should also include the appropriate private statements at the beginning of the class to make the object variables global.
Class CompressedFolder
Private m_fileName
Private m_ignoreConflicts
Private objShell
Private objFso
…
Here I’ve added the objShell and objFso declarations to the top of my code class. I’ve also added m_ignoreConflicts, which is another global variable used throughout some of my methods.
Finally, the Class_Terminate routine is executed when the class object is released. This provides a good place to release any global objects.
Okay, some of you are scratching your heads wondering why I would bother releasing those objects, right? It’s true that any objects will be released whenever the class terminates anyway. I more or less just wanted to demonstrate how the Terminate event could be used. This particular class doesn’t actually have a solid use for the Terminate event.
Now that you’ve built your class, you can begin implementing it in your scripts. You’ll need to copy and paste the class into your script to begin with. Just like a function or subroutine, it doesn’t matter where you place it as long as it’s in the global scope. Then you’ll need to connect to it like this:
Set objZipFolder = New CompressedFolder
Remember that classes return objects, so you’ll need to use a Set statement to assign the return value. The New keyword followed by a class name tells VBScript that we’re instantiating a class. You can instantiate as many instances of a class as necessary.
If you’re using a script editor with an IntelliSense feature, it should have no problem displaying the public properties and methods for your object. Here’s what it looks like in Sapien’s PrimalScript 2007.
If you plan on using this class in a development environment, I highly suggest that you take the time to download the latest version here. I do update my scripts from time to time to add new features or fix bugs. The full documentation for this class is also available here.
I hope you’ve had fun learning how to create your own VBScript classes. Learning to use classes effectively can greatly reduce the amount of work you do, while providing a much more professional look to your code. Until next time, keep coding!
Code Examples 
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Implementing the CompressedFolder Class
