nature_net.user_controls.custom_listbox._list_PreviewTouchMove C# (CSharp) Метод

        private void _list_PreviewTouchMove(object sender, TouchEventArgs e)
        {
            FrameworkElement findSource = e.OriginalSource as FrameworkElement;
            ListBoxItem element = null;
            while (element == null && findSource != null)
                if ((element = findSource as ListBoxItem) == null)
                    findSource = VisualTreeHelper.GetParent(findSource) as FrameworkElement;

            if (element != null)
                last_dragged_element = element;
            this.touch_points.Add(e.GetTouchPoint(this._list as IInputElement));
            if (touch_points.Count < configurations.min_touch_points) return;
            double dy = touch_points[touch_points.Count - 1].Position.Y - touch_points[touch_points.Count - 2].Position.Y;
            double dx = touch_points[touch_points.Count - 1].Position.X - touch_points[touch_points.Count - 2].Position.X;
            double size_n = Math.Sqrt(dx * dx + dy * dy);
            dx = dx / size_n; dy = dy / size_n;
            if (dx == double.NaN || dy == double.NaN) return;
            double theta1 = Math.Acos(dx * drag_direction1.X + dy * drag_direction1.Y);
            double theta2 = Math.Acos(dx * drag_direction2.X + dy * drag_direction2.Y);
            //convert to degree
            theta1 = theta1 * 180 / Math.PI;
            theta2 = theta2 * 180 / Math.PI;
            double theta = (theta1 < theta2) ? theta1 : theta2;
            if (theta < configurations.drag_collection_theta)
            {
                if (consecutive_drag_points < configurations.max_consecutive_drag_points)
                {
                    consecutive_drag_points++;
                }
                else
                {
                    if (is_tap.ContainsKey(e.TouchDevice.Id)) is_tap[e.TouchDevice.Id] = false;
                    if (element == null) element = last_dragged_element;
                    if (element != null)
                    {
                        avatar_drag(element, e.TouchDevice);
                        touch_points.Clear();
                        consecutive_drag_points = 0;
                        e.Handled = true;
                        return;
                    }
                }
            }
            ScrollViewer scroll = configurations.GetDescendantByType(this._list, typeof(ScrollViewer)) as ScrollViewer;
            double dv = touch_points[touch_points.Count - 1].Position.Y - touch_points[0].Position.Y;
            dx = touch_points[touch_points.Count - 1].Position.X - touch_points[0].Position.X;
            //double new_offset = scroll.HorizontalOffset + (-1 * configurations.scroll_scale_factor * dx);
            if (dv > configurations.tap_error || dx > configurations.tap_error)
                if (is_tap.ContainsKey(e.TouchDevice.Id)) is_tap[e.TouchDevice.Id] = false;
            double new_offset = last_scroll_offset + (-1 * dv);
            try { scroll.ScrollToVerticalOffset(new_offset); }
            catch (Exception) { }
        }