What's an reusable, but simple and efficient way to Disallow special characters ("\ / : ? " < > |") in a WPF TextBox?

Question

I have several WPF TextBoxes in my application that will be used for specifying file names. I'm looking for a solution that will quickly and easily allow me to disallow special characters (i.e. "\ / : ? " < > |") from being entered into these textboxes, without having to create a custom control that inherits from TextBox and doesn't require the use of Regular Expressions.

Answer 1

I created a static class called "DisallowSpecialCharatersTextBoxBehavior" that that harnesses the power of Attachable Properties in WPF, like so:

public static class DisallowSpecialCharactersTextboxBehavior
{
    public static DependencyProperty DisallowSpecialCharactersProperty =
        DependencyProperty.RegisterAttached("DisallowSpecialCharacters", typeof(bool), typeof(DisallowSpecialCharactersTextboxBehavior), new PropertyMetadata(DisallowSpecialCharactersChanged));

    public static void SetDisallowSpecialCharacters(TextBox textBox, bool disallow)
    {
        textBox.SetValue(DisallowSpecialCharactersProperty, disallow);
    }

    public static bool GetDisallowSpecialCharacters(TextBox textBox)
    {
        return (bool)textBox.GetValue(DisallowSpecialCharactersProperty);
    }

    private static void DisallowSpecialCharactersChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs e)
    {
        var tb = dependencyObject as TextBox;
        if (tb != null)
        {

            if ((bool)e.NewValue)
            {
                tb.PreviewTextInput += tb_PreviewTextInput;
                tb.AddHandler(DataObject.PastingEvent, new DataObjectPastingEventHandler(tb_Pasting));
            }
            else
            {
                tb.PreviewTextInput -= tb_PreviewTextInput;
                tb.RemoveHandler(DataObject.PastingEvent, new DataObjectPastingEventHandler(tb_Pasting));
            }

        }
    }

    private static void tb_Pasting(object sender, DataObjectPastingEventArgs e)
    {
        var pastedText = e.DataObject.GetData(typeof(string)) as string;

        Path.GetInvalidFileNameChars().ToList().ForEach(c =>
            {
                if (pastedText.Contains(c))
                {
                    e.CancelCommand();
                }

            });
    }

    private static void tb_PreviewTextInput(object sender, System.Windows.Input.TextCompositionEventArgs e)
    {
        if (Path.GetInvalidFileNameChars().ToList().ConvertAll(x => x.ToString()).Contains(e.Text))
        {
            e.Handled = true;
        }

    }
}

It can easily be applied to any TextBox in WPF like so:

<Window x:Class="ExampleApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:ExampleApp"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <TextBox local:DisallowSpecialCharactersTextboxBehavior.DisallowSpecialCharacters="true"  />
    </Grid>
</Window>