private void RectangleSelection_PointerMoved(object sender, PointerRoutedEventArgs e)
{
if (scrollViewer == null)
{
return;
}
var currentPoint = e.GetCurrentPoint(uiElement);
var verticalOffset = scrollViewer.VerticalOffset;
if (selectionState == SelectionState.Starting)
{
if (!HasMovedMinimalDelta(originDragPoint.X, originDragPoint.Y - verticalOffset, currentPoint.Position.X, currentPoint.Position.Y))
{
return;
}
// Clear selected items once if the pointer is pressed and moved
selectionStrategy.StartSelection();
OnSelectionStarted();
selectionState = SelectionState.Active;
}
if (currentPoint.Properties.IsLeftButtonPressed)
{
var originDragPointShifted = new Point(originDragPoint.X, originDragPoint.Y - verticalOffset); // Initial drag point relative to the topleft corner
base.DrawRectangle(currentPoint, originDragPointShifted, uiElement);
// Selected area considering scrolled offset
var rect = new System.Drawing.Rectangle((int)Canvas.GetLeft(selectionRectangle), (int)Math.Min(originDragPoint.Y, currentPoint.Position.Y + verticalOffset), (int)selectionRectangle.Width, (int)Math.Abs(originDragPoint.Y - (currentPoint.Position.Y + verticalOffset)));
foreach (var item in itemsPosition.ToList())
{
try
{
if (rect.IntersectsWith(item.Value))
{
selectionStrategy.HandleIntersectionWithItem(item.Key);
}
else
{
selectionStrategy.HandleNoIntersectionWithItem(item.Key);
}
}
catch (ArgumentException)
{
// Item is not present in the ItemsSource
itemsPosition.Remove(item);
}
}
if (currentPoint.Position.Y > uiElement.ActualHeight - 20)
{
// Scroll down the list if pointer is at the bottom
var scrollIncrement = Math.Min(currentPoint.Position.Y - (uiElement.ActualHeight - 20), 40);
scrollViewer.ChangeView(null, verticalOffset + scrollIncrement, null, false);
}
else if (currentPoint.Position.Y < 20)
{
// Scroll up the list if pointer is at the top
var scrollIncrement = Math.Min(20 - currentPoint.Position.Y, 40);
scrollViewer.ChangeView(null, verticalOffset - scrollIncrement, null, false);
}
}
}