How to make keyboardevent common to other files in C# WPF?

Question

I have a PreviewKeyDown event in my code like below:

    private void Box_PreviewKeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.Space)
        {
            e.Handled = true;
        }
        if ((e.Key == Key.V) && (e.KeyboardDevice.Modifiers & ModifierKeys.Control) != 0)
        {
            e.Handled = true;
        }
        else
        {
            base.OnKeyDown(e);
        }
    }

This code runs blocking Ctrl+V and space key in TextBox or PasswordBox control in wpf.

What I want to do is making this code as common and call this code in PasswordBox in another file.

Any solution? I know I can allocate PreviewKeyDown event to each control but it is repeated so I want to avoid duplication.

Answer 1

One option would be to wrap the functionality in a reusable attached behaviour:

public static class Behavior
{
    public static bool GetHandlePreviewKeyDown(UIElement element) =>
        (bool)element.GetValue(HandlePreviewKeyDownProperty);

    public static void SetHandlePreviewKeyDown(UIElement element, bool value) =>
        element.SetValue(HandlePreviewKeyDownProperty, value);

    public static readonly DependencyProperty HandlePreviewKeyDownProperty =
        DependencyProperty.RegisterAttached(
        "HandlePreviewKeyDown",
        typeof(bool),
        typeof(Behavior),
        new UIPropertyMetadata(false, OnChanged));

    private static void OnChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        UIElement element = (UIElement)d;
        bool value = (bool)e.NewValue;
        if (value)
            element.PreviewKeyDown += Element_PreviewKeyDown;
        else
            element.PreviewKeyDown -= Element_PreviewKeyDown;
    }

    private static void Element_PreviewKeyDown(object sender, KeyEventArgs e) =>
        e.Handled = (e.Key == Key.Space) || ((e.Key == Key.V) && (e.KeyboardDevice.Modifiers & ModifierKeys.Control) != 0);
}

Usage:

<TextBox local:Behavior.HandlePreviewKeyDown="true" />