Introduction

This article is written for an audience of Visual Basic for Applications (VBA) programmers. Specifically, VBA programmers wanting to write code for Bentley Systems MicroStation^® VBA.

Questions similar to this appear on the Bentley Discussion Groups.

Q How can I measure a LineElement?

A We can write a locator class that lets a user select a LineElement, then measure the length of the selected element.

This article shows how to start a Locator class from a UserForm, locate a LineElement, then display the line's length on the UserForm.

Q Communication with a class …

• How can I pass information between two VBA classes?
• How can I pass information to and from a class that Implements ILocateCommandEvents?

A A class object can include private variables that you can assign using a class Property. For example, if you have a UserForm that starts a locator class, then you can set a property in your locator that informs it about its originator. The locator class can then call methods of the originator.

This article shows how to create a Locator class from a UserForm, then set a reference to the UserForm in the locator class. The locator class can subsequently user that reference to call methods or properties of the UserForm.

VBA Solution

A line is represented by a LineElement object. One of its properties is Length (in the model's master units). We need to locate a LineElement in a model and display its length on a form. From the user's perspective, the sequence of operation is …

1. Run the MeasureLine project
   • the modeless UserForm shows
2. Click the Measure Line button
   • the locator class starts and prompts the user to identify a LineElement
3. User identifies a valid element
   • the locator class updates the Length textbox on the UserForm

As a VBA programmer, you'll see that the UserForm creates the locator class and sets a reference to itself. The locator class then has a mechanism to call methods & properties of its originator. Next, the code invokes CommandState.StartLocate that starts the locate events. When the user has identified a valid element, the locator class sets the UserForm's Length property.

Locator Class

The locator is a VBA class module that Implements ILocateCommandEvents. We customise the event handlers to accept only LineElements. We include a reference to the UserForm that called the class, then use that form's methods to show the length of the located element.

The key to inter-class communication is the member variable that holds a reference to the originating class …

' ---------------------------------------------------------------------
'   Member variable stores a reference to the UserForm that called this
'   locate class
' ---------------------------------------------------------------------
Private m_oOriginator                       As frmLocator
' ---------------------------------------------------------------------
'   Property lets us assign our form to this variable
'   e.g. Set oLocator.Originator = Me
' ---------------------------------------------------------------------
Public Property Set Originator(ByRef oForm As frmLocator)
    Set m_oOriginator = oForm
End Property

UserForm

The UserForm is a VBA form module. The Measure Line button has a _Click event that creates the locator class, sets the property that references itself, then starts the locate operation …

Private Sub cmdMeasure_Click()
    '   Start a new locate command by invoking our class clsLocator
    Dim oLocator As New clsLocator
    Set oLocator.Originator = Me
    CommandState.StartLocate oLocator
End Sub

VBA Project

The VBA project has three modules …

1. Normal module modMain that contains the project entry point subroutine Main
2. Class module clsLocator that Implements ILocateCommandEvents
3. Form module frmLocator that provides a user interface

Start the tool using the MicroStation keyin: vba run [MeasureLine]modMain.Main

Download the Line Filter

You can download the Measure Line MVBA project. The project includes the MVBA project MeasureLine.mvba.

• Unpack the ZIP archive to a suitable location, such as C:\Program Files\Bentley\Workspace\Standards\vba
• Start the tool with the MicroStation keyin: vba run [MeasureLine]modMain.Main