WPF Simple Validation Question - setting custom ErrorContent

Question

If I have the following TextBox:

Answer 1

You can use ValidationRules.

For instance, in my case, when a user enters an invalid value into a decimal datagridtextcolumn, instead of the default message "Value could not be converted" I can override it with:

and here's the code for the DecimalRule:

public override ValidationResult Validate(object value, CultureInfo cultureInfo)
{
    decimal convertedDecimal;
    if (!decimal.TryParse((string)value, out convertedDecimal))
    {
        return new ValidationResult(false, "My Custom Message"));
    }
    else
    {
        return new ValidationResult(true, null);
    }
}