Custom Functions

Updated on May 7, 2026

This article aims to show a sample approach how to create a custom function, |Abs|, for returning the absolute value of the current entry in the calculator. The |Abs| button will replace the 1/x button:

Default functions	Custom function

The exact implementation of the custom calculation is just a sample approach. It may be customized according to the specific custom requirements that need to be covered.

C#

public class CustomCalculator : RadCalculator
{
    public override string ThemeClassName
    {
get
{
    return typeof(RadCalculator).FullName;
}
    }
    protected override RadCalculatorElement CreateCalculatorElement()
    {
return new CustomRadCalculatorElement();
    }
}

public class CustomRadCalculatorElement : RadCalculatorElement
{
    protected override Type ThemeEffectiveType
    {
get
{
    return typeof(RadCalculatorElement);
}
    }

    protected override RadCalculatorContentElement CreateContentElement()
    {
return new CustomRadCalculatorContentElement(this);
    }
}

public class CustomRadCalculatorContentElement : RadCalculatorContentElement
{
    public CustomRadCalculatorContentElement(ICalculatorElement owner) : base(owner)
    {
    }

    protected override void CreateChildElements()
    {
base.CreateChildElements();
this.ButtonReciprocal.Visibility = ElementVisibility.Collapsed;
RadCalculatorOperationButtonElement button = new RadCalculatorOperationButtonElement("|Abs|", CalculatorAction.None);
button.SetValue(Telerik.WinControls.Layouts.GridLayout.RowIndexProperty, 3);
button.SetValue(Telerik.WinControls.Layouts.GridLayout.ColumnIndexProperty, 4);
button.Click += Button_Click;
button.SetValue(Telerik.WinControls.Layouts.GridLayout.CellPaddingProperty, new Padding(3));
this.GridLayout.Children.Add(button);
    }

    private void Button_Click(object sender, EventArgs e)
    {
RadCalculatorElement calcElement = this.Owner as RadCalculatorElement;

decimal entry = 0;
if (decimal.TryParse(calcElement.CalculationBehavior.DisplayedValue, out entry))
{
    calcElement.CalculationBehavior.ClearEverything();
    calcElement.CalculationBehavior.ClearStacksAndHistory();
    calcElement.CalculationBehavior.Value = Math.Abs(entry);
    calcElement.CalculationBehavior.DisplayedValue = calcElement.CalculationBehavior.Value.ToString(calcElement.Culture);
}
    }
}

VB.NET

Public Class CustomCalculator
Inherits RadCalculator

Public Overrides Property ThemeClassName As String
    Get
        Return GetType(RadCalculator).FullName
    End Get
    Set(value As String)
        MyBase.ThemeClassName = value
    End Set
End Property
Protected Overrides Function CreateCalculatorElement() As RadCalculatorElement
    Return New CustomRadCalculatorElement()
End Function
End Class

Public Class CustomRadCalculatorElement
Inherits RadCalculatorElement

Protected Overrides ReadOnly Property ThemeEffectiveType As Type
    Get
        Return GetType(RadCalculatorElement)
    End Get
End Property

Protected Overrides Function CreateContentElement() As RadCalculatorContentElement
    Return New CustomRadCalculatorContentElement(Me)
End Function
End Class

Public Class CustomRadCalculatorContentElement
Inherits RadCalculatorContentElement

Public Sub New(ByVal owner As ICalculatorElement)
    MyBase.New(owner)
End Sub

Protected Overrides Sub CreateChildElements()
    MyBase.CreateChildElements()
    Me.ButtonReciprocal.Visibility = ElementVisibility.Collapsed
    Dim button As RadCalculatorOperationButtonElement = New RadCalculatorOperationButtonElement("|Abs|", CalculatorAction.None)
    button.SetValue(Telerik.WinControls.Layouts.GridLayout.RowIndexProperty, 3)
    button.SetValue(Telerik.WinControls.Layouts.GridLayout.ColumnIndexProperty, 4)
    AddHandler button.Click, AddressOf Button_Click
    button.SetValue(Telerik.WinControls.Layouts.GridLayout.CellPaddingProperty, New Padding(3))
    Me.GridLayout.Children.Add(button)
End Sub

Private Sub Button_Click(ByVal sender As Object, ByVal e As EventArgs)
    Dim calcElement As RadCalculatorElement = TryCast(Me.Owner, RadCalculatorElement)
    Dim entry As Decimal = 0

    If Decimal.TryParse(calcElement.CalculationBehavior.DisplayedValue, entry) Then
        calcElement.CalculationBehavior.ClearEverything()
        calcElement.CalculationBehavior.ClearStacksAndHistory()
        calcElement.CalculationBehavior.Value = Math.Abs(entry)
        calcElement.CalculationBehavior.DisplayedValue = calcElement.CalculationBehavior.Value.ToString(calcElement.Culture)
    End If
End Sub
End Class

See Also

• Design Time
• Getting Started