Classic VB - How do I detect if an index exists in a control array?

By using the VarType function provided by VB we get rather odd results: it returns the default property's data type for controls that exist and are initialized while the unused indexes give the more expected result of vbObject. Since none of the controls default property returns an object we can safely use this as our detection.

Thus to check whether a control index already exists, start a new project and add a new command button, name it cmdArray and set it's Index to 0 in the property window, then paste:

Code:

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Private Sub Form_Load()
    Dim intA As Integer
   
    Load cmdArray(5)
    Load cmdArray(3)
    Load cmdArray(1)
    Load cmdArray(2)
   
    For intA = cmdArray.LBound To cmdArray.UBound
        If VarType(cmdArray(intA)) <> vbObject Then
            Debug.Print "Index " & intA & " exists!"
        Else
            Debug.Print "Index " & intA & " IS MISSING!"
        End If
    Next
End Sub

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You get:
Index 0 exists!
Index 1 exists!
Index 2 exists!
Index 3 exists!
Index 4 IS MISSING!
Index 5 exists!


If you wish to have an easy-to-use function, then this will do:

Code:

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Public Function HasIndex(ControlArray As Object, ByVal Index As Integer) As Boolean
    HasIndex = (VarType(ControlArray(Index)) <> vbObject)
End Function

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