WPF Validating unbound textbox - wpf

Question

is it possible to use validation without the Binding part? The thing is my textbox is not bound to any object, but I still want to validate it's content. The only way I've found so far is this:
<TextBox Grid.Row="0" Grid.Column="1" MaxLength="50" x:Name="textBoxTubeName" Margin="5,5,0,5">
<TextBox.Text>
<Binding Path="Name" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" NotifyOnValidationError="True">
<Binding.ValidationRules>
<validation:InvalidCharactersRule />
</Binding.ValidationRules>
</Binding>
</TextBox.Text>
</TextBox>
But again, it only works when the TextBox.Text is bound to something (in this case, the Name property), how would I go about this without binding?
Thanks!

Answer 1

According to the MSDN forums it's not possible yet but it is planned (Note: this is an old post). However, I still can't find a way to do it so it may not be implemented yet.

Answer 2

It is a lot tricky to do from code-behind. Basically, you can set a temporary binding from code and raise the validation error and when the input has valid value you can remove all the temporary binding stuff again.
Here what I use, which I consider a bad practise (but it's better from nothing):
/// <summary>
/// Marks a textBox control as invalid (via validation error) from code.
/// </summary>
/// <param name="textBox">The text box.</param>
/// <param name="errorContent">Content of the error.</param>
public static void ValidationMarkInvalid(TextBox textBox, String errorContent)
{
DependencyProperty textProp = TextBox.TextProperty;
if (!BindingOperations.IsDataBound(textBox, textProp))
{
if (textBox.DataContext == null)
{
textBox.DataContext = new EmptyDataContext();
}
Binding b = new Binding("CodeBehind");
b.FallbackValue = textBox.Text;
b.ValidatesOnExceptions = true;
BindingOperations.SetBinding(textBox, textProp, b);
}
BindingExpression bindingInError =
textBox.GetBindingExpression(TextBox.TextProperty);
var validationError = new ValidationError(
new EmptyValidationRule(),
bindingInError,
errorContent,
new Exception(errorContent));
Validation.MarkInvalid(bindingInError, validationError);
}
/// <summary>
/// Clears the validation error from a textBox.
/// </summary>
/// <param name="textBox">The text box.</param>
public static void ValidationClear(TextBox textBox)
{
DependencyProperty textProp = TextBox.TextProperty;
if (BindingOperations.IsDataBound(textBox, textProp))
{
String value = textBox.Text;
Validation.ClearInvalid(textBox.GetBindingExpression(TextBox.TextProperty));
BindingOperations.ClearBinding(textBox, textProp);
textBox.Text = value;
EmptyDataContext ctx = textBox.DataContext as EmptyDataContext;
if (ctx != null)
{
textBox.DataContext = null;
}
}
}
#region Nested Type: EmptyDataContext
private sealed class EmptyDataContext : INotifyPropertyChanged
{
public Object CodeBehind
{
get
{
throw new FormatException();
}
set
{
throw new FormatException();
}
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
#endregion
}
#endregion
#region Nested Type: EmptyValidationRule
private sealed class EmptyValidationRule : ValidationRule
{
/// <summary>
/// When overridden in a derived class, performs validation checks on a value.
/// </summary>
/// <param name="value">The value from the binding target to check.</param>
/// <param name="cultureInfo">The culture to use in this rule.</param>
/// <returns>
/// A <see cref="T:System.Windows.Controls.ValidationResult"/> object.
/// </returns>
public override ValidationResult Validate(Object value, CultureInfo cultureInfo)
{
return new ValidationResult(false, String.Empty);
}
}
#endregion
Now, from your code-behind you do this:
ValidationMarkInvalid(textBox, "Please enter something valid!");
and to clear the validation:
ValidationClear(textBox);
P.S.: If you don't want to validate on exceptions you can remove the EmptyDataContext class from the above methods.