AttachedDependencyProperties_UpdateSide.cs

private static void UpdateSide(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var obj = (FrameworkElement)d;

    // Finding the LeftRightLayoutControl to which this object belongs to either directly or indirectly.
    var parent = LogicalTreeHelper.GetParent(obj);
    while (parent != null && parent.GetType() != typeof(LeftRightLayoutControl))
    {
        parent = LogicalTreeHelper.GetParent(parent);
    }
    var layoutControl = (LeftRightLayoutControl)parent;

    // Detaching the object from the current logical parent.
    ((StackPanel)obj.Parent).Children.Remove(obj);

    // Reattaching the object to the correct logical parent based on the new value.
    var value = (Side)e.NewValue;
    if (value == Side.Left)
    {
        layoutControl._left.Children.Add(obj);
    }
    else if (value == Side.Right)
    {
        layoutControl._right.Children.Add(obj);
    }
    else
    {
        layoutControl.Children.Add(obj);
    }
}