Force validation on button click   

Hi there,

I've created a validation rule that checks if a field is empty, and
attached it to a TextBox.
However, the validation only occurs when I type something in and tab
out of the textbox. Is there a way to programmatically force
validation to occur when I click a button on a form?


    public class NotEmptyValidationRule : ValidationRule
    {
        public override ValidationResult Validate(object value,
System.Globalization.CultureInfo cultureInfo)
        {
            string s = (string)value;
            if (String.IsNullOrEmpty(s))
                return new ValidationResult(false, "Cannot be
empty.");
            return new ValidationResult(true, null);
        }
    }


        <TextBox HorizontalAlignment="Right" Margin="0,133,19,152"
Name="textBox3" Width="120" >
            <TextBox.Text>
                <Binding Path="FirstName">
                    <Binding.ValidationRules>
                        <local:NotEmptyValidationRule />
                    </Binding.ValidationRules>
                </Binding>
            </TextBox.Text>
        </TextBox>

date: Tue, 16 Oct 2007 12:00:42 -0700   author:   Oleg Ogurok