Enable the Object Level Event

Before you can use object level events you must create a new class module and declare an object of type AcadObject with events. For example, assume that a new class module is created and called EventClassModule. The new class module contains the declaration of the application with the VBA keyword WithEvents.

To create a new class and declare a Circle object with events

  1. In the VBA IDE, insert a class module. From the Insert menu, choose Class Module.
  2. Select the new class module in the Project window.
  3. Change the name of the class in the Properties window to EventClass-Module.
  4. Open the Code window for the class using F7, or by selecting the menu option View Code.
  5. In the Code window for the class, add the following line:
Public WithEvents Object As AcadCircle

After the new object has been declared with events, it appears in the Object drop-down list box in the class module, and you can write event procedures for the new object in the class module. (When you select the new object in the Object box, the valid events for that object are listed in the Procedure drop-down list box.)

Before the procedures will run, however, you must connect the declared object in the class module with the Circle object. You can do this with the following code from any module.

To connect the declared object to the Automation object

  1. In the Code window for your main module, add the following line to the declarations section:
    Dim X As New EventClassModule
  2. In the same window, create a circle called “MyCircle” and initialize it as containing events:
    Sub InitializeEvents()
     Dim MyCircle As AcadCircle
     Dim centerPoint(0 To 2) As Double
     Dim radius As Double
     centerPoint(0) = 0#: centerPoint(1) = 0#: centerPoint(2) = 0#
     radius = 5#
     Set MyCircle = ThisDrawing.ModelSpace.AddCircle(centerPoint, radius)
     Set X.Object = MyCircle
    End Sub
  3. In the code for your main module, add a call to the InitializeApp subroutine:
    Call InitializeEvents

    Once the InitializeEvents procedure has been run, the Circle object in the class module points to the Circle object created, and any event procedures in the class module will run when the events occur.

    NoteWhen coding in VBA, you must provide an event handler for all objects enabled for the Modified event. If you do not provide a handler, VBA may terminate unexpectedly.
    Display the area of a closed polyline whenever the polyline is updated

    This example creates a lightweight polyline with events. The event handler for the polyline then displays the new area whenever the polyline is changed. To trigger the event, simply change the size of the polyline in AutoCAD. Remember that you must run the CreatePLineWithEvents subroutine before the event handler is activated.

    Public WithEvents PLine As AcadLWPolyline
    Sub CreatePLineWithEvents()
     ' This example creates a light weight polyline
     Dim points(0 To 9) As Double
     points(0) = 1: points(1) = 1
     points(2) = 1: points(3) = 2
     points(4) = 2: points(5) = 2
     points(6) = 3: points(7) = 3
     points(8) = 3: points(9) = 2
     Set PLine = ThisDrawing.ModelSpace. _
     PLine.Closed = True
    End Sub
    Private Sub PLine_Modified _
     (ByVal pObject As AutoCAD.IAcadObject)
     ' This event is triggered when the polyline is resized.
     ' If the polyline is deleted the modified event is still
     ' triggered, so we use the error handler to avoid
     ' reading data from a deleted object.
     MsgBox "The area of " & pObject.ObjectName & " is: " _
     & pObject.Area
     Exit Sub
     MsgBox Err.Description
    End Sub