Edit

RowSourceType property (user-defined function) code argument values

  • Article

The Visual Basic function that you create must accept five arguments. The first argument must be declared as a control and the remaining arguments as Variants. The function itself must return a Variant.

Function functionname (fld As Control, id As Variant, row As Variant, col As Variant, code As Variant) As Variant

The Function procedure has the following five required arguments.

Argument Description
fld A control variable that refers to the list box or combo box being filled.
id A unique value that identifies the control being filled. This is useful when you want to use the same user-defined function for more than one list box or combo box and must distinguish between them. (The example sets this variable to the value of the Timer function.)
row The row being filled (zero-based).
col The column being filled (zero-based).
code An intrinsic constant that specifies the kind of information being requested.

Note

Because Microsoft Access calls a user-defined function several times to insert items into a list, often you must preserve information from call to call. The best way to do this is to use Static variables.

Microsoft Access calls the user-defined function by repeatedly using different values in the code argument to specify the information it needs. The code argument can use the following intrinsic constants.

Constant Meaning Function returns
acLBInitialize Initialize Nonzero if the function can fill the list; False (0) or Null otherwise.
acLBOpen Open Nonzero ID value if the function can fill the list; False or Null otherwise.
acLBGetRowCount Number of rows Number of rows in the list (can be zero); -1 if unknown.
acLBGetColumnCount Number of columns Number of columns in the list (can't be zero); must match the property sheet value.
acLBGetColumnWidth Column width Width (in twips) of the column specified by the col argument; -1 to use the default width.
acLBGetValue List entry List entry to be displayed in the row and column specified by the row and col arguments.
acLBGetFormat Format string Format string to be used to format the list entry displayed in the row and column specified by the row and col arguments; -1 to use the default format.
acLBEnd End (the last call to a user-defined function always uses this value) Nothing.
acLBClose (Not used) Not used.

Access calls your user-defined function once for acLBInitialize, acLBOpen, acLBGetRowCount, and acLBGetColumnCount. It initializes the user-defined function, opens the query, and determines the number of rows and columns.

Access calls your user-defined function twice for acLBGetColumnWidth—once to determine the total width of the list box or combo box and a second time to set the column width.

The number of times your user-defined function is called for acLBGetValue and acLBGetFormat to get list entries and to format strings varies depending on the number of entries, the user's scrolling, and other factors.

Access calls the user-defined function for acLBEnd when the form is closed or each time the list box or combo box is queried.

Whenever a particular value (such as the number of columns) is required, returning Null or any invalid value causes Access to stop calling the user-defined function with that code.

Tip

Use the Select Case code structure from the example as a template for your own RowSourceType property user-defined functions.

Example

The following user-defined function returns a list of the next four Mondays following today's date. To call this function from a list box control, enter ListMondays as the RowSourceType property setting and leave the RowSource property setting blank.

Public Function ListMondays(fld As Control, id As Variant, _
    row As Variant, col As Variant, code As Variant) _ 
    As Variant 

    Dim Offset      As Integer
    Dim WeekdayDate As Date 
 
    Select Case code 
        Case acLBInitialize     ' Initialize. 
            ListMondays = True 
        Case acLBOpen           ' Open. 
            ListMondays = Timer ' Unique ID. 
        Case acLBGetRowCount    ' Get rows. 
            ListMondays = 4 
        Case acLBGetColumnCount ' Get columns. 
            ListMondays = 1 
        Case acLBGetColumnWidth ' Get column width. 
            ListMondays = -1    ' Use default width. 
        Case acLBGetValue       ' Get the data. 
            Offset = Abs((9 - Weekday(Date)) Mod 7) 
            WeekdayDate = DateAdd("d", _
                Offset + 7 * row, Date) 
            ListMondays = Format(WeekdayDate, _
                "mmmm d") 
    End Select 

End Function

The next example uses a static array to store the names of the databases in the current directory. To call this function, enter ListMDBs as the RowSourceType property setting and leave the RowSource property setting blank.

Public Function ListMDBs(fld As Control, id As Variant, _ 
    row As Variant, col As Variant, code As Variant) _
    As Variant 
    
    Static dbs(127) As String
    Static Entries  As Integer 
    Dim ReturnVal   As Variant 

    ReturnVal = Null 
    Select Case code 
        Case acLBInitialize     ' Initialize. 
            Entries = 0 
            dbs(Entries ) = Dir("*.MDB") 
            Do Until dbs(Entries) = "" Or Entries >= 127 
                Entries = Entries + 1 
                dbs(Entries) = Dir 
            Loop 
            ReturnVal = Entries 
        Case acLBOpen           ' Open. 
            ' Generate unique ID for control. 
            ReturnVal = Timer 
        Case acLBGetRowCount    ' Get number of rows. 
            ReturnVal = Entries 
        Case acLBGetColumnCount ' Get number of columns. 
            ReturnVal = 1 
        Case acLBGetColumnWidth ' Column width. 
            ' -1 forces use of default width. 
            ReturnVal = -1 
        Case acLBGetValue       ' Get data. 
            ReturnVal = dbs(row) 
        Case acLBEnd            ' End. 
            Erase dbs 
    End Select 
    ListMDBs = ReturnVal 
    
End Function

Support and feedback

Have questions or feedback about Office VBA or this documentation? Please see Office VBA support and feedback for guidance about the ways you can receive support and provide feedback.