VBScript Classes pt2 – Properties

This week I thought I’d continue the discussion on classes, from my previous article on the subject (VBScript Classes pt1). One of the nice things about classes is the ability to call and manipulate them like variables, while having a lot of code in line to do things along the way.

Last week you saw we can embed functions (and subs) within classes to give encapsulation, but you can also embed some new method types “properties”.

An example of a typical method, is the good old wscript object. You’re probably very familiar with wscript for example:

wscript.echo "Hello World"

Here we call the wscript object, ‘echo’ method and send it “Hello World” a parameter. This is akin to calling a sub within VBS.

How about if we want to do something akin to setting or retrieving the title of an explorer window?

objIE.document.title = "Hello World"
wscript.echo objIE.document.title

Though it might not be obvious – something very interesting is happening here – you can both set the title, and get the title using the same call, depending on the situation.

this is what class ‘properties’ give you. We can set both “get” and “let” properties with the same name to handle the situation where we are retrieving, or storing a value. Of course we don’t have to set both, you can have read-only and write-only properties if you like.

I’ve created a simple example below for you – it’s an address book program using two classes. One called clsIDCard which is a simplistic name and phone number handler, and one called clsAddressBook which maintains a list of cards, lets you get and add them, and retrieve how many cards there are.

Now, you could use a few arrays to do this, but using classes lets us add some clever functionality.

for example, when we add a card in this example, we get to set a value for objTempCard.fullname (in the add sub of clsAddressBook). This in turn goes through the property add code in clsIDCard, which you can see extracts the first and surname into the card object.

Thus, even though we’re just setting some values with our call, the data’s being manipulated on the fly for us.

The addressbook itself ends up as an array of idCard objects, so all the code in clsIDCard can be used for each of them – if we wanted to add validation, new fields of information etc, we can do that in isolation of any other piece of code (though we might want to expand the ‘add’ function to make it easier to handle them). Also if we want to change the layout of the ‘card’ property, we can do that without changing the addressbook logic.

I hope this helps you get ‘classes’ into your head. Feel free to comment if not.

Option Explicit
Class clsidCard
    Private strSur, strFirst,strMobile
    Property Let surname(str)
        strSur = str
    End Property
    Property Get surname
    End Property
    Property let firstname(str)
        strFirst = str
    End Property
    Property Get firstname
    End Property
    Property Let fullname(str)
        strfirst = trim(left(str, InStr(str," ")))
        strsur = Trim(Mid(str, InStr(str," ")))
    End Property
    Property Get fullname
        fullname= strfirst & " " & strSur
    End Property
    Property Let mobile(str)
    End Property
    Property Get mobile
    End Property
    Property Get card
        card="Name: " & fullname & vbNewLine & "Mobile: " & mobile
    End Property
End Class

Class clsAddressBook
    Public addressbook()

    Sub class_initialize
        ReDim addressbook(0)
    End Sub

    Sub add(ByVal strName,ByVal strMobile)
        Dim objTempCard
        If IsObject(addressbook(UBound(addressbook))) Then
            ReDim Preserve addressbook(UBound(addressbook)+1)
        End If
        Set objTempCard = New clsidCard
        objtempcard.fullname = strName
        objTempCard.mobile= strMobile
        set addressbook(UBound(addressbook)) = objtempcard
    End Sub

    Function getcard(index)
        set getcard = addressbook(index)
    End Function

    Property Get count
        count= UBound(addressbook)+1
    End Property
End Class

Dim idCard : Set idcard = New clsidCard
Dim addressbook : Set addressbook = New clsAddressBook

addressbook.add "Simon Hunt","239 298 7000"
addressbook.add "John Smith","239 298 7001"
addressbook.add "Alice Bob","239 298 7003"

Dim i
For i = 0 To addressbook.count-1
Set idCard = addressbook.getcard(i)
 WScript.Echo "Card: " & i & vbNewLine & idCard.card & vbNewLine
  1. July 11, 2009 at 06:15

    Great posts, Simon, now where is the class for sbadmcl 🙂 ?

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