RadNumericUpDown Validation Using IDataErrorInfo Interface

Environment

Product Version	2022.3.1109
Product	RadNumericUpDown for WPF

Description

How to validate the Value property of the RadNumericUpDown control on custom criteria.

Solution

To achieve this functionality, you can implement the IDataErrorInfo interface in your view model.

Implementing IDataErrorInfo interface

C#

    public class NumericUpDownViewModel : ViewModelBase, IDataErrorInfo
    {
    	private double numericUpDownValue;

        public NumericUpDownViewModel()
        {
            this.NumericUpDownValue = -5;
        }

        public double NumericUpDownValue
        {
            get { return this.numericUpDownValue; }
            set
            {
                this.numericUpDownValue = value;
                this.OnPropertyChanged(nameof(this.NumericUpDownValue));
            }
        }

        public string Error
        {
            get { return this[string.Empty]; }
        }

        public string this[string name]
        {
            get
            {
                string result = null;

                if (name == "NumericUpDownValue")
                {
                    return this.ValidateValue();
                }

                return result;
            }
        }

        private string ValidateValue()
        {
            if (this.NumericUpDownValue < 0)
            {
                return "Value cannot be a negative number";
            }

            return null;
        }
    }

VB.NET

    Public Class NumericUpDownViewModel
        Inherits ViewModelBase
        Implements IDataErrorInfo
        Private numericUpDownValueField As Double

        Public Sub New()
            NumericUpDownValue = -5
        End Sub

        Public Property NumericUpDownValue As Double
            Get
                Return numericUpDownValueField
            End Get
            Set(ByVal value As Double)
                numericUpDownValueField = value
                Me.OnPropertyChanged(NameOf(Me.NumericUpDownValue))
            End Set
        End Property

        Public ReadOnly Property [Error] As String
            Get
                Return Me(String.Empty)
            End Get
        End Property

        Default Public ReadOnly Property Item(ByVal name As String) As String
            Get
                Dim result As String = Nothing

                If Equals(name, "NumericUpDownValue") Then
                    Return ValidateValue()
                End If

                Return result
            End Get
        End Property

        Private Function ValidateValue() As String
            If NumericUpDownValue < 0 Then
                Return "Value cannot be a negative number"
            End If

            Return Nothing
        End Function
    End Class

Binding the Value property of RadNumericUpDown

XAML

    <telerik:RadNumericUpDown Value="{Binding NumericUpDownValue, Mode=TwoWay, ValidatesOnDataErrors=True}" UpdateValueEvent="PropertyChanged"/>

In order for the RadNumericUpDown control to show its Validation.ErrorTemplate when an error occurs, set the ValidatesOnDataErrors property of the Binding instance to True.

RadNumericUpDown with a validation error and error message