ACC: How to Create an AfterUndo Form Event

MORE INFORMATION

When you click Undo Record on the Edit menu or press the ESC key twice to undo changes to the current record in a form, there is no built-in form event that is triggered. The AfterUndo procedure simulates an AfterUndo event so that you can restore calculations that may have been set while the record was being edited.

Creating the AfterUndo Procedure

To create the AfterUndo procedure, follow these steps:

1. Open the form to which you want to add the AfterUpdate procedure in Design view, and then add a text box with the following properties to the form:

   Name: txtEditModeChange
   ControlSource: =[Form].[Dirty] & CheckUndo([Form])
   Visible: No

2. Add the following event procedure to the AfterUpdate property of the form:

         Sub Form_AfterUpdate ()
         ' Because the record is being saved, which changes the edit mode, the
         ' bookmark should be reset so that it will appear to the CheckUndo()
         ' function that the user moved to another record.
            PrevBookmark = Null
         End Sub
   						

3. Add the following lines to the Declarations section of the form module if they are not already there:

         Option Explicit
         Dim PrevBookmark

4. Add the following procedures to the form module:

         Function CheckUndo (F As Form) As Variant
            Dim CurrBookmark
   
            ' Is the record clean (not dirty)?
            If Not F.Dirty Then
               ' If so, get the current bookmark.
               On Error Resume Next
               CurrBookmark = F.bookmark
   
               ' If an error occurred, this is the new record.
               If Err Then CurrBookmark = "NewRecord"
   
               ' Determine if the edit change occurred on the same record (the
               ' record was undone, as opposed to moving to another record).
                If StrComp(CurrBookmark, PrevBookMark, 0) = 0 Then
                  ' The record was undone.
                  AfterUndo
               Else
                  ' The record was not undone (moved to another
                  ' record). Record the bookmark of the current
                  ' record for the next iteration.
                  PrevBookmark = CurrBookmark
               End If
            End If
   
         End Function
   
         Sub AfterUndo ()
           ' Add the code you want to run when the record is undone here.
         End Sub
   						

How to Use the AfterUndo Procedure

The following example demonstrates how to use the AfterUndo procedure:

1. Open the sample database Northwind.mdb (or NWIND.MDB in version 2.0).
2. Open the Employees form in Design view and follow steps 1 through 4 of the "Creating the AfterUndo Procedure" section earlier in this article.
3. Modify the code in the AfterUndo procedure (created in step 4) as follows:

         Sub AfterUndo ()
            MsgBox "Record Changes Undone"
         End Sub
   						

4. View the form in Form view.
5. Modify any field in any record in the form.
6. On the Edit menu, click Undo Current Field/Record (Undo Current Record in Microsoft Access 2.0 and 7.0). Note that the "Record Changes Undone" message box appears.
7. On the Edit menu, click Go To, and then click New Record (click New in Microsoft Access 2.0 and 7.0).
8. Type any text in any field in the new record.
9. Press the ESC key. Note that the "Record Changes Undone" message box appears.