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Display Custom Error Message in RadMaskedInput

Environment

Product RadMaskedInput for WPF

Description

Implement custom validation by adding a ValidationError in code.

Solution

If you want to mark the state of the control as invalid and display an error message in the RadMaskedInput controls and you do not want to throw validation exceptions or use data annotations, you can manually set a validation error in code by using the ValidationError class and the Validation.MarkInvalid method.

private void MaskedInput_ValueChanged(object sender, Telerik.Windows.RadRoutedEventArgs e) 
{ 
    var input = sender as RadMaskedTextInput; 
    if (input.Value == "123") 
    { 
        var rule = new ExceptionValidationRule(); 
 
        ValidationError validationError = new ValidationError(rule, this.MaskedInput.GetBindingExpression(RadMaskedTextInput.ValueProperty)); 
        validationError.ErrorContent = "The input is invalid!"; 
 
        Validation.MarkInvalid(this.MaskedInput.GetBindingExpression(RadMaskedTextInput.ValueProperty), validationError); 
    } 
    else 
    { 
        Validation.ClearInvalid(this.MaskedInput.GetBindingExpression(RadMaskedTextInput.ValueProperty)); 
    } 
} 
You can notice that the Validation.ClearInvalid method can be used if the state of the binding should be marked as valid.

For this approach to work as expected, a binding to the Value property of the control needs to be set.

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