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05 May 2003

**This Client Server article is republished in its entirety from 2003 for reference purposes.**

05 May 2003

This article describes how to write a recursive routine to solve a complex problem by solving progressively simpler problems, until a final base case can be reached. There are many practical applications to apply the theory of recursion for any nested object in MicroStation objects such as cells, attachments, etc.

# What is recursive method?

Recursive definitions are common in mathematics. Any series in which a term is defined using the values of earlier terms in the series is a recursive definition. For example, the sum of the first n integers can be defined as the value of n plus the sum of the first n-1 integers.

Here is a recursive function to compute this sum:

Function sumNumber (n As Integer) As Integer

If n <= 1 Then ‘Base case

sumNumber = 1

Else ‘ the recursive call

sumNumber = sumNumber(n - 1) + n

End If

End Function

As illustrated above, you can see that a recursive function has two cases:

1. The base case - If the problem is simple enough, it is solved without recursive calls. In the above example, the sum of the 1st integer is 1.

2. The recursive call - The function calling itself to solve a simpler problem, as in the above example, would call itself by calculating the sum of the current n-1 integers.

# Recursive method usage in Microstation VBA

As mentioned previously, a recursive function has many practical applications in MicroStation. For example, in the managing of nested cells, the base case is always a primitive element (such as line, shape, text, ellipse, etc.), which cannot be broken down to a simpler case to manage.

For example:

To change the color of a shape element, we can:

Dim oShapeElement As ShapeElement

‘ ....... Get oShapeElement from scan,

‘ user pick from model, or create one

oShapeElement.Color = 4 'Change element color

‘rewrite changes to its model.

oShapeElement.Rewrite

‘Redraws this object on the view

ShapeElement.Redraw msdDrawingModeNormal

To change the font of a text element:

Dim oFont As Font

Set oFont = ActiveDesignFile.Fonts(3)

With oTextElement

.TextStyle.Font = oFont

.Rewrite

End With

To process a cell element, the solution to apply would use an ElementEnumerator similar to:

Dim oElEnum As ElementEnumerator

Set oElEnum = oCellElement.GetSubElements

Do While oElEnum.MoveNext

‘ ..... Process each element inside a cell

Loop

In a recursive call, the function will keep calling itself to solve a simpler problem until the base case has been satisfied.

This code illustrates how a recursive function call is used to list all elements within a nested cell:

Function processNestedCell (oCellElement As _

CellElement) As Variant

Dim oElEnum As ElementEnumerator

Dim oSubElement As Element

Set oElEnum = oCellElement.GetSubElements

Do While oElEnum.MoveNext

Set oSubElement = oElEnum.Current

If oSubElement.Type = msdElementTypeCellHeader _

Then

Debug.Print "Nested Cell Name: " & _ oSubElement.AsCellElement.Name

' Recursive call

processNestedCell oSubElement.AsCellElement

Else

' Base case, not a cell element,

‘ If needed, you can check more type,

' Such as if type is text or text node

‘ do something, ....

Debug.Print oSubElement.Type

'More control on each type element.

‘Such as change Ellipse color

If oSubElement.Type = _

msdElementTypeEllipse Then

oSubElement.AsEllipseElement.Color = 4

'Change element color

oSubElement.Rewrite

oSubElement.Redraw msdDrawingModeNormal

End If

End If

Loop

End Function

Upon receiving a list of elements within a complex nested cell you can now easily manage and process each individual base case elements, performing any required operation such as changing the symbology or properties.

Note: If you are performing an operation that would attempt to change the size of a complex object it is recommended that you do not simply delete individual elements in cell. Instead, create a new cell with of the correct size and delete the old one.

# Where should I use recursion?

Try taking these concepts further and see if you can use recursion to manage other complex element types in MicroStation such as reference files, etc.

# See Also

MicroStation Desktop TechNotes and FAQs

# Comments or Corrections?

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