Access Cookbook, 2nd Edition [Electronic resources] نسخه متنی

Recipe 6.2 Determine if You're on a New Record in a Form

6.2.1 Problem

Often, you need to do different things
depending on whether the current row is the
"new" row on a form. For example,
you might want to display a certain message box only when adding
records. How can you do this?

6.2.2 Solution

You can use a form's
NewRecord property to determine if you are on a new record by
checking its value from an event procedure attached to the OnCurrent
event property or some other event property of the form.

Follow these steps to implement this functionality in your own forms:

1. Create a new form or modify the design of an existing form.

2. Create an event procedure for the
   form's Current event. In that event procedure,
   create an If...Then statement that will branch
   based on the value of the form's NewRecord property.
   The code of the event procedure should look like this:

   Private Sub Form_Current( )
   If Me.NewRecord Then
   ' Do something for a new record.
   Else
   ' Do something for an existing record.
   End If
   End Sub

3. You may wish to alter some visual
   cue on the form to indicate whether you are on a new record. For
   example, you might change the text of a label, the text of the
   form's titlebar, or the picture of an image control.
   In the sample form, we changed the picture of an image control in the
   form's header, imgFlag, by copying the picture from
   one of two hidden image controls that are also located on the form.
   The final Current event procedure looks like this:

   Private Sub Form_Current( )
   ' Determine if this is a new record and change the bitmap
   ' of the imgFlag control to give the user visual feedback.
   ' See the Solution in Recipe 9.7 for an explanation of using the
   ' PictureData property.
   If Me.NewRecord Then
   Me.imgFlag.PictureData = Me.imgFlagNew.PictureData
   Else
   Me.imgFlag.PictureData = Me.imgFlagEdit.PictureData
   End If
   End Sub

4. Create any additional code that reacts
   to the NewRecord property. In the sample form, we decided to remind
   the user to log in the new record when saving it. Thus, we created
   the following event procedure attached to the form's
   BeforeUpdate event:

   Private Sub Form_BeforeUpdate(Cancel As Integer)
   Dim strMsg As String
   If Me.NewRecord Then
   strMsg = "You just added a new record " & _
   "(# " & Me.ContactID & ")" & vbCrLf & _
   "Please don't forget to log it in!"
   Beep
   MsgBox strMsg, vbOKOnly + vbInformation, "New Record Added"
   End If
   End Sub

To see an example, load and open frmContacts from

06-02.MDB . Notice that the picture in the
upper-left corner of the form changes to indicate whether you are
editing an existing record (Figure 6-3) or adding a
new record (Figure 6-4). In addition, when you save
a newly added record, a message box is displayed that reminds you to
log the new record (Figure 6-4). The message box
does not appear when you save changes to an existing record.

Figure 6-3. The sample form indicates that you are editing an existing record

Figure 6-4. The sample form indicates that you are adding a record

6.2.3 Discussion

The NewRecord property is simple: its
value is True when adding a new record and
False otherwise. This property is
True from the moment the pending new record
becomes current until the moment the record is saved. NewRecord is
reset to False right after the BeforeUpdate event;
it is False during both the AfterUpdate and
AfterInsert events.

The image control used to display the
add/edit icon uses a trick to change its picture quickly. Rather than
loading a bitmap image from a disk file, which would be slow, it
copies the picture from one of two hidden
"source" image controls on the
form.

To do this, set the image control's PictureData
property to the value of the PictureData property of another image
control. Chapter 9 discusses the PictureData
property in more detail.