Using the Formula Wizard to Add Your Own Functions

The formula wizard and its features are among the most important and powerful capabilities of the Designer. Using a special List & Label component for the OCX, you can also integrate fully customized functions into the Designer. To use the control, you must include the file cmll29fx.ocx in your IDE.

To add a new function, insert this component on a form at the time of design. You can now set the necessary parameters in the Properties window of this component.

Property	Description
Name	The unique name of the designer function.
Description	An additional description of the function for the formula wizard.
GroupName	The group in which the function is displayed in the formula wizard.
Visible	Indicates whether or not the function will be displayed in the wizard.
MinimumParameters	The minimum number of parameters. Permissible values between 0 and 4.
MaximumParameters	The maximum number of parameters. Here too, permissible values between 0 and 4. The value must be equal to or greater than the minimum number. Increasing the number results in optional parameters.
ResultType	The data type of the return value.

Using the properties, you can customize the configuration of the new Designer function. The parameters for the design functions are defined in the source code. This may look as follows:

Visual Basic:

Private Sub InitializeDesFunction()

       Dim param1 As DesignerFunctionsParameter
       Dim param2 As DesignerFunctionsParameter

       Set param1 = DesFunc_Add.Parameter1
       param1.Description = "First Value"
       param1.Type = LlParamType.ParamType_Double

       Set param2 = DesFunc_Add.Parameter2
       param2.Description = "Second Value"
       param2.Type = LlParamType.ParamType_Double

       DesFunc_Add.ParentComponent = ListLabel1
End Sub

In order to bring the function to life, you have to handle the event DesFunc_Add_EvaluateFunction. Using the event arguments, you gain access to the parameters entered by the user. For example, to return the sum of the two parameters, use the following lines:

Visual Basic:

Private Sub DesFunc_Add_EvaluateFunction(ResultValue As Variant,
                ResultType As CMLL29FXLibCtl.LlParamType,
                DecimalPositions As Long,
                ByVal Parameters As Long, ByVal Parameter1 As Variant,
                ByVal Parameter2 As Variant, ByVal Parameter3 As Variant,
                ByVal Parameter4 As Variant)

       ResultValue = CDbl(Parameter1) + CDbl(Parameter2)
       ResultType = ParamType_Double

End Sub

Two additional events also give you the option to further modify the function. DesFunc_Add_CheckFunctionSyntax lets you perform a syntax check. Here you can check the data types of the parameters and, for example, make sure the parameters fall within a certain range. DesFunc_Add_ParameterAutoComplete allows you to define several suggested values for the AutoComplete feature of the formula wizard.