How to suppress validation when nothing is entered

Question

I use WPF data binding with entities that implement IDataErrorInfo interface. In general my code looks like this:

Business entity:

p         


        

Answer 1

I believe this behavior to also be a good solution. It removes ErrorTemplate on TextBox when needed and also supports multiple "valid" invalid values (you can also improve it by making ValidInputs a dependency property).

public class NotValidateWhenSpecified : Behavior
{
    private ControlTemplate _errorTemplate;

    public string[] ValidInputs { get; set; } = { string.Empty };

    protected override void OnAttached()
    {
        AssociatedObject.TextChanged += HideValiationIfNecessary;

        _errorTemplate = Validation.GetErrorTemplate(AssociatedObject);
        Validation.SetErrorTemplate(AssociatedObject, null);
    }        

    protected override void OnDetaching()
    {
        AssociatedObject.TextChanged -= HideValiationIfNecessary;
    }

    private void HideValiationIfNecessary(object sender, TextChangedEventArgs e)
    {
        if (ValidInputs.Contains(AssociatedObject.Text))
        {                
            if (_errorTemplate != null)
            {
                _errorTemplate = Validation.GetErrorTemplate(AssociatedObject);
                Validation.SetErrorTemplate(AssociatedObject, null);
            }                
        }
        else
        {
            if (Validation.GetErrorTemplate(AssociatedObject) != _errorTemplate)
            {
                Validation.SetErrorTemplate(AssociatedObject, _errorTemplate);
            }                
        }
    }
}