ACC2000: Error When Object Methods Rely on Optional Arguments

If an object's method within a subroutine or a function uses the optional arguments allowed by the subroutine or the function, and one or more of the optional arguments are excluded at the time that the subroutine or the function is called, one of the following run-time errors can occur:

The object's method is expecting one or more of its arguments to have some value, and one of the arguments has either been assigned an unknown value, or the value has been excluded altogether.

Functions such as IsMissing() or IsNull() within Visual Basic for Applications can be used to check for any excluded optional arguments. Within the subroutine or the function that is called, programmatically test to see if one or more of the optional arguments was excluded. For example:

1. Type the following two procedures into a new module:

   Sub Prog1(Optional a, Optional b, Optional c)
       If IsMissing(a) Then a = acDefault
       If IsMissing(b) Then b = ""
       If IsMissing(C) Then c = acSavePrompt
       DoCmd.Close a, b, c
   End Sub
   
   Sub Prog2(Optional a As Long, Optional b As String, Optional c As Long)
       If a = 0 Then a = acDefault
       If IsNull(b) Then b = ""
       If C = 0 Then c = acSavePrompt
       DoCmd.Close a, b, c
   End Sub
   					

2. Press CTRL+G to open and move focus to the Immediate window.
3. Type the following line in the Immediate window, and then press ENTER:

   Prog1
   					

4. Type the following line in the Immediate window, and then press ENTER:

   Prog2
   					

If you have programmatically specified that one or more arguments of a method should be used, and you do not supply an argument at run time or you do not supply a valid value for an argument, you will receive the run-time error.

To illustrate this point, the "Steps to Reproduce Behavior" section will use the Close method of the DoCmd object within a subroutine, where the subroutine allows for optional arguments. However, when the subroutine is called, the optional arguments are excluded in order to generate the run-time error.

Steps to Reproduce Behavior

1. Open the sample database Northwind.mdb.
2. Create a new module and type the following procedure:

   Sub Prog(Optional a, Optional b, Optional c)
      DoCmd.Close a, b, c
   End Sub
   					

3. Save the module as modTest.
4. Press CTRL+G to open and move focus to the Immediate window.
5. Type the following line in the Immediate window, and then press ENTER:

   Prog
   						

   
   Note that you receive the "Type Mismatch" run-time error.
6. Modify the arguments within the subroutine as follows:

   Sub Prog(Optional a As Long, Optional b As String, Optional c As Long)
   					

7. Repeat steps 3 through 5.
   
   Note that you receive the "This action requires an Object Name argument" run-time error.