How to handle exception in Value converter so that custom error message can be displayed

Question

I have a textbox that is bound to a class with a property of type Timespan, and have written a value converter to convert a string into TimeSpan.

If a non number is

Answer 1

I used validation and converter to accept null and numbers

XAML:

Code Behind:

private void Validation_Error(object sender, ValidationErrorEventArgs e)
{
    if (e.Action == ValidationErrorEventAction.Added)
        _noOfErrorsOnScreen++;
    else
        _noOfErrorsOnScreen--;
}

private void Confirm_CanExecute(object sender, CanExecuteRoutedEventArgs e)
{
    e.CanExecute = _noOfErrorsOnScreen == 0;
    e.Handled = true;
}

ValidationRule :

public class NumericFieldValidation : ValidationRule
{
    private const string InvalidInput = "Please enter valid number!";

    // Implementing the abstract method in the Validation Rule class
    public override ValidationResult Validate(object value, System.Globalization.CultureInfo cultureInfo)
    {
        float val;
        if (!string.IsNullOrEmpty((string)value))
        {
            // Validates weather Non numeric values are entered as the Age
            if (!float.TryParse(value.ToString(), out val))
            {
                return new ValidationResult(false, InvalidInput);
            }
        }

        return new ValidationResult(true, null);
    }
}

Converter :

public class NullableValueConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (string.IsNullOrEmpty(value.ToString()))
            return null;
        return value;
    }
}