ACC: How to Use Optional Arguments

ID: Q141605


The information in this article applies to:
  • Microsoft Access versions 7.0, 97


SUMMARY

Advanced: Requires expert coding, interoperability, and multiuser skills.

When you use the Optional keyword in Microsoft Access 7.0 and 97, you can create procedures that accept optional (not required) arguments. This article shows you two examples of how to create and use procedures with optional arguments.

This article assumes that you are familiar with Visual Basic for Applications and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Visual Basic for Applications, please refer to your version of the "Building Applications with Microsoft Access" manual.


MORE INFORMATION

NOTE: In Microsoft Access 7.0, it was required that the variables declared as optional were placed at the end of the calling procedure and that the data type was explicitly a Variant. For example:


   Sub MyTest(strTest1 As String, _
       Optional Test2 As Variant, _
       Optional Test3 As Variant) 
This was a requirement because optional arguments were passed at the end of the function call. In Microsoft Access 97 improvements have been made to the use of the Optional keyword by allowing the data type casting of the optional variable to be pre-assigned. For example:

    Sub MyTest(strTest1 As String, _
       Optional Test2 As String = "Test2", _
       Optional Test3 As String = "Test3") 
This allows for the placement of the optional variable anywhere in the calling order of the function and allows you to test the contents of the variable.

Example 1

  1. Create a module and type the following line in the Declarations section if it isn't already there:
    
          Option Explicit 


  2. Type the following procedure:
    
          Function CallEmployeeInfo()
             If Forms!employees!Title <> "Sales Representative" Then
               EmployeeInfo Forms!employees!FirstName, Forms!employees!LastName
             Else
               EmployeeInfo Forms!employees!FirstName, _
               Forms!employees!LastName, Forms!employees!Title
             End If
          End Function
    
          Sub EmployeeInfo(fname, lname, Optional Title)
             If IsMissing(Title) Then
                MsgBox lname & ", " & fname
             Else
                MsgBox lname & ", " & fname & "   " & Title
             End If
    
          End Sub 


  3. Open the Employees form in Form view.


  4. To test this function, type the following line in the Debug window, and then press ENTER:
    ? CallEmployeeInfo()
    Note that the message box opens. If the title is not Sales Representative, then the option title argument is not sent to the Sub routine but the Sub routine will still process. It just displays the two arguments that were provided. If the title is Sales Representative, the argument title is sent and displayed in the message box.


Example 2

  1. Create a module and type the following line in the Declarations section if it isn't already there:
    
         Option Explicit 


  2. Type the following procedure:
    
          Sub OptionalTest(Optional Country)
             Dim dbs As DATABASE, rst As Recordset
             Dim strSQL As String
    
             ' Return Database variable pointing to current database.
             Set dbs = CurrentDb
             If IsMissing(Country) Then
                strSQL = "SELECT * FROM Orders"
                'This will return all the records
             Else
                strSQL = "SELECT * FROM Orders WHERE [ShipCountry] = '" &_
                Country & "';"
             'This will return only values matching the argument you entered.
             End If
             Set rst = dbs.OpenRecordset(strSQL)
             rst.MoveLast
             Debug.Print rst.RecordCount
    
          End Sub 


  3. Type the following line in the Debug window, and then press ENTER:
    OptionalTest "UK"
    Note that the record count will return the number of records where the ShipCountry is equal to UK.


  4. Type the following line in the Debug window, and then press ENTER:
    OptionalTest
    Note that you receive a record count for the whole table. This is because the optional argument was not supplied when the Sub procedure was called. This feature can be very useful for setting up criteria for queries.



REFERENCES

For more information about the Optional keyword, search the Help Index for "optional argument," or ask the Microsoft Access 97 Office Assistant.

Additional query words:

Keywords : kbprg
Version : WINDOWS:7.0,97
Platform : WINDOWS
Issue type : kbhowto


Last Reviewed: October 20, 1999
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