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Tip of the Day
Language: Visual Basic
Expertise: Beginner
Aug 8, 1997



Building the Right Environment to Support AI, Machine Learning and Deep Learning

Using the Undocumented Count Property of Control Arrays

In VB4, each control array is its own collection and therefore has a Count property. This was not the case in version 3. It is now possible to loop through all of the elements of a control array without having to hard-code the maximum value of the array index.

This feature is not documented in the VB4 manuals or online help. The likely reason for this is that a control array collection does not support all of the standard methods and properties of a "real" collection. The Count property and the Item method are supported, but the Add and Remove methods are not.

This simple example uses the Count property to determine which element of an array of option buttons has been selected:

Private Sub FindSelectedOption ( )

        Dim ii As Integer

        For ii = 0 To Option1.Count - 1
                If Option1(ii).Value Then
                MsgBox "Option Button " & ii _
                        & " is selected."
                End If
        Next ii

End Sub

This procedure will only work if the array indices are continuous, with no gaps in the sequence. If, for example, the control array consists of elements 0, 1, 3, 4, the above procedure will generate a runtime error 340 when it tries to evaluate Option1(2), and even if this first error is trapped, Option1(4) will never be reached in the loop, and therefore will not be evaluated.

Craig Everett
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