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

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; 
    } 
} 

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

<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