IsMissing

concerns

You can use the IsMissing function to check whether an optional parameter has been specified when passing parameters to a function. If the parameter is specified or if the specified variable is not an optional parameter, the function returns False, otherwise True.

 

Syntax
IsMissing(Variable)
Return value
Type	Description
Boolean	True if the variable was not specified during parameter transfer
Parameter
Use	Name	Type	Passing	Description
Required	Variable	Variable	ByVal	Variable

 

The following example uses the optional Gloss parameter. If this is not specified when the function is called, this is detected using the IsMissing function. In the further sequence, the RGB color values of the passed RAL code are determined.

 

SetColor(3001)

 

Function SetColor(ByVal RALCode As Long, Optional ByVal Gloss As Long) As Void

   If IsMissing(Gloss) Then

      Gloss := 1

   End If

  

   Dim Col As New TCEGDIP.GDIPColor, ARGB As Long

  

   ARGB := Col.RALtoARGB(RALCode)

   Col.Value := ARGB

  

   MsgBox(Col.Red & " " & Col.Green & " " & Col.Blue & " Gloss " & Gloss)

  

  

End Function

 

Alternatively, a default value can be specified for optional parameters: In this example, the check with IsMissing can be omitted.

 

Function SetColor(ByVal RALCode As Long, Optional ByVal Gloss As Long := 1) As Void

  

   Dim Col As New TCEGDIP.GDIPColor, ARGB As Long

  

   ARGB := Col.RALtoARGB(RALCode)

   Col.Value := ARGB

  

   MsgBox(Col.Red & " " & Col.Green & " " & Col.Blue & " Gloss " & Gloss)

  

  

End Function