How to pass optional arguments to a method on an ActiveX Control

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1. Optional arguments must appear at the end of the parameter list. If an optional argument is omitted when calling the method, all arguments to the right of this one must also be omitted. This is similar to the C++ rules for calling functions with Default values for parameters.
2. Optional arguments must be declared as VARIANTs. If a parameter is omitted, the calling program must pass a VARIANT initialized as:

      VARIANT.vt = VT_ERROR
      VARIANT.scode = DISP_E_PARAMNOTFOUND.
   						

   This will be done automatically by Visual Basic. However, in Visual C++ you must create and initialize the VARIANT yourself.NOTE: If using Visula Studio.NET do the following:
3. You must edit the IDL file generated for the control and mark the parameters as optional. This is done by adding the [optional] tag as shown here:

   [id(1)] void MyOpt([optional] VARIANT param1,
               [optional] VARIANT param2);
   						

1. Using ClassWizard, add a new method to the control. Be sure to pick VARIANT as the type for each optional argument, and be sure the optional arguments appear last in the parameter list.
   
   NOTE: If using Visual Studio .NET do the following:
   
   In Class View, expand the project node to display the interface that you want to add the method. Click Add, and then click Add Method. Pick VARIANT as the type for each optional argument, and verify that the optional arguments appear last in the parameter list.
2. Edit the ODL file, and mark these parameters with the [optional] tag.
3. Add the appropriate functionality to the method and rebuild the control.
   
   For example, the MyOpt method defined in ODL syntax above could be called from Visual Basic in the following three forms:

      myocx.MyOpt 2, 3  'passing both args
      myocx.MyOpt 2     'omit one arg
      myocx.MyOpt       'omit both args