Sub ClearCustomFunctions() 

Dim instance As ICustomFunctionSupport2
 
instance.ClearCustomFunctions()

void ClearCustomFunctions()

<Serializable()>
public class CubeFunctionInfo : FarPoint.CalcEngine.FunctionInfo 
{ 
        public override string Name { get { return "CUBE"; } } 
        public override int MinArgs { get { return 1; } } 
        public override int MaxArgs { get { return 1; } } 
        public override object Evaluate (object[] args) 
        { 
            double num = FarPoint.CalcEngine.CalcConvert.ToDouble(args[0]); 
            return num * num * num; 
        } 
} 
    
FarPoint.Web.Spread.Model.ICustomFunctionSupport cfs; 
cfs = (FarPoint.Web.Spread.Model.ICustomFunctionSupport)FpSpread1.ActiveSheetView.DataModel; 
cfs.AddCustomFunction(new CubeFunctionInfo()); 
FpSpread1.ActiveSheetView.SetFormula(1, 1, "CUBE(4)"); 

private void Button1Click(object sender, System.EventArgs e)
{
    FarPoint.Web.Spread.Model.ICustomFunctionSupport2 cfs2; 
    cfs2 = (FarPoint.Web.Spread.Model.ICustomFunctionSupport2)FpSpread1.ActiveSheetView.DataModel; 
    cfs2.ClearCustomFunctions();
    FpSpread1.ActiveSheetView.Recalculate();
}

<Serializable()> 
Public Class CubeFunctionInfo
   Inherits FarPoint.CalcEngine.FunctionInfo

   Public Overrides ReadOnly Property Name() As String
        Get
             Return "CUBE"
        End Get
   End Property

   Public Overrides ReadOnly Property MinArgs() As Integer
        Get
             Return 1
        End Get
   End Property

   Public Overrides ReadOnly Property MaxArgs() As Integer
        Get
             Return 1
        End Get
   End Property

   Public Overrides Function Evaluate(ByVal args() As Object) As Object
        Dim num As Double = FarPoint.CalcEngine.CalcConvert.ToDouble(args(0))
        Return num * num * num
   End Function
End Class

Dim cfs As FarPoint.Web.Spread.Model.ICustomFunctionSupport
cfs = FpSpread1.ActiveSheetView.DataModel
cfs.AddCustomFunction(New CubeFunctionInfo)
FpSpread1.ActiveSheetView.SetFormula(1, 1, "CUBE(4)")

Private Sub Button1Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Dim cfs2 As FarPoint.Web.Spread.Model.ICustomFunctionSupport2
    cfs2 = FpSpread1.ActiveSheetView.DataModel
    cfs2.ClearCustomFunctions()
    FpSpread1.ActiveSheetView.Recalculate()
End Sub