/// <summary>
/// Returns a RegexValidationRule to be used for validating the specified TextBox.
/// If the TextBox is not yet initialized, this method returns null.
/// </summary>
static RegexValidationRule GetRegexValidationRuleForTextBox(TextBox textBox)
{
if (!textBox.IsInitialized)
{
// If the TextBox.Text property is bound, but the TextBox is not yet
// initialized, the property's binding can be null. In that situation,
// hook its Initialized event and verify the validation rule again when
// that event fires. At that point in time, the Text property's binding
// will be non-null.
EventHandler callback = null;
callback = delegate
{
textBox.Initialized -= callback;
VerifyRegexValidationRule(textBox);
};
textBox.Initialized += callback;
return(null);
}
// Get the binding expression associated with the TextBox's Text property.
BindingExpression expression = textBox.GetBindingExpression(TextBox.TextProperty);
if (expression == null)
{
throw new InvalidOperationException(
"The TextBox's Text property must be bound for the RegexValidator to validate it.");
}
// Get the binding which owns the binding expression.
Binding binding = expression.ParentBinding;
if (binding == null)
{
throw new ApplicationException(
"Unexpected situation: the TextBox.Text binding expression has no parent binding.");
}
// Look for an existing instance of the RegexValidationRule class in the
// binding. If there is more than one instance in the ValidationRules
// then throw an exception because we don't know which one to modify.
RegexValidationRule regexRule = null;
foreach (ValidationRule rule in binding.ValidationRules)
{
if (rule is RegexValidationRule)
{
if (regexRule == null)
{
regexRule = rule as RegexValidationRule;
}
else
{
throw new InvalidOperationException(
"There should not be more than one RegexValidationRule in a Binding's ValidationRules.");
}
}
}
// If the TextBox.Text property's binding does not yet have an
// instance of RegexValidationRule in its ValidationRules,
// add an instance now and return it.
if (regexRule == null)
{
regexRule = new RegexValidationRule();
binding.ValidationRules.Add(regexRule);
}
return(regexRule);
}