Using Recursion in VBA

Written by Rod Wing.

Using Recursion in VBA

Recursion is a programming technique where a sub or function calls itself. There are many examples where this can come in very useful and eliminate a lot of copying and pasting of code. A common task in MicroStation where this can be put to use is iterating through groups of elements containing both simple and complex elements using an ElementEnumerator.

The following ProcessText function illustrates how recursion can be used to filter out and modify text elements from a set of elements. Text Node and Cell elements are two types of complex elements that can contain simple text elements that we want to process. Using the GetSubElements  method of a complex element type we can obtain a new ElementEnumerator and call the ProcessText function again to look for text elements inside the complex element.


Public Function ProcessText(ee As ElementEnumerator) As Boolean
    Dim i As Long
    Dim iStart As Long
    Dim iEnd As Long
    Dim elArray() As Element
    ProcessText = False
    If ee Is Nothing Then
        Exit Function
    End If
    elArray = ee.BuildArrayFromContents
    iStart = LBound(elArray)
    iEnd = UBound(elArray)
    For i = iStart To iEnd
        Select Case elArray(i).Type
            Case MsdElementType.msdElementTypeText
                With elArray(i).AsTextElement
                    ' Modify text element here
                End With
            Case MsdElementType.msdElementTypeTextNode
                ' GetSubElement returns an ElementEnumerator containing text elements within text node
                ' use recursive function call to process new enumerator
                If Not ProcessText(elArray(i).AsTextNodeElement.GetSubElements) Then
                    Exit Function
                End If
            Case MsdElementType.msdElementTypeCellHeader
                ' GetSubElement returns an ElementEnumerator containing elements within cell
                ' use recursive function call to process new enumerator to process any text elements in cell
                If Not ProcessText(elArray(i).AsCellElement.GetSubElements) Then
                    Exit Function
                End If
        End Select
    ProcessText = True
    Exit Function
    MsgBox "ProcessText Error: " & CStr(Err.Number) & Err.Description
End Function


Rod Wing

Rod is the Senior Systems Analyst at EnvisionCAD and has extensive experience in GIS, cartography, plotting, scanning, raster editing/manipulation, publishing, and file/data translations. He instructs MicroStation classes ranging from fundamentals to advanced.


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