Tips and Techniques for Setting and Validating Microsoft Access Combo Box
Provided by: Luke Chung, FMS President
Microsoft Access forms and table datasheets support
Combo Boxes to let your users easily enter a selection by providing them
with a list of valid values. This makes sure your data is correct and
Sample combo box listing countries from
Total Zip Code Database
Most commonly, the list of values is from a table or
query, and can be bound to one field (like an ID field) while displaying
a field the user sees and understands. Combo boxes in Access also
support the display of multiple columns so you can show more data to
make it easier to select the right item.
Setting Combo Box Display Properties
Here are some tips for using Combo Boxes effectively.
Total Access Analyzer
flags any combo boxes in your tables and forms that don't have these
properties set correctly:
Set LimitToList to Yes
Set the LimitToList property to Yes, otherwise users can
enter values that are not in your list.
Set AutoExpand to Yes
Set the AutoExpand property to Yes to automatically select a matching
value in the list as you type.
It's annoying to see a short list of options and be
forced to scroll to see the remaining few items, or to have a long list
and be forced to scroll more than necessary because the number of rows
displayed is small -- even though there's plenty of room on the screen!
Increase the ListRows property to display more choices
and minimize the need to scroll. The default is number of rows is 8 in
Access 2003 or earlier. It is increased to 16 in Access 2007, but that's
still low. We would recommend 25 or 30+ if space allows. If the list
doesn't have that many rows, the higher number has no impact.
Selecting the First Item with the
With an unbound Combo Box, you may want to display the
first item by default rather than showing a blank value. To do this, use
the combo box's ItemData object. ItemData is an array of the combo box
For instance, a combo box named cboCountry can be set to
the first value in the list by adding this code to the form's OnLoad
Me.cboCountry = Me.cboCountry.ItemData(0)
Properly Validating Combo Boxes with the ListIndex
In forms, the BeforeUpdate event is used to validate the
entries in the current record. For Combo Boxes, people often check if
the value exists by looking for Null like this (where cboName is the
name of the combo box):
If IsNull(Me.cboName) Then
MsgBox "A value is required for ..."
Cancel = True
This flags a missing value, prompts the user, and sets
focus to the control, works in most cases, but not all.
If the combo box is on a bound field, there may be an
existing value which is not valid. With the combo box set to LimitToList,
the field has a value, but you can't see it. Maybe the value was in the
list when it was originally selected, but the current list of allowed
values has changed.
If you simply check for IsNull, Access says it is not
null (which is correct) and you don't handle the invalid entry. What you
really want to know is if a valid value was selected. A better check is
with the ListIndex property:
If Me.cboName.ListIndex = -1 Then
MsgBox "A value is required for ...."
Cancel = True
There is no need to check for Null. The ListIndex
property returns the number of the selected item (ranges from 0 to the
number of items in the list minus 1). If no value or an invalid item is
selected, it returns -1 and you can trap it.
Resources for Microsoft Access Forms, Combo Boxes and Tabs