/// <summary>
/// When overridden in a derived class, participates in rendering operations that are directed by the layout system.
/// The rendering instructions for this element are not used directly when this method is invoked, and are instead preserved for
/// later asynchronous use by layout and drawing.
/// </summary>
/// <param name="drawingContext">The drawing instructions for a specific element. This context is provided to the layout system.</param>
protected override void OnRender(DrawingContext drawingContext)
{
var dropInfo = DropInfo;
if (dropInfo.VisualTarget is ItemsControl itemsControl)
{
// Get the position of the item at the insertion index. If the insertion point is
// to be after the last item, then get the position of the last item and add an
// offset later to draw it at the end of the list.
var visualTargetItem = dropInfo.VisualTargetItem;
var itemParent = visualTargetItem != null?ItemsControl.ItemsControlFromItemContainer(visualTargetItem) : itemsControl;
// this could be happen with a thread scenario where items are removed very quickly
if (itemParent == null)
{
return;
}
var itemsCount = itemParent.Items.Count;
var index = Math.Min(dropInfo.InsertIndex, itemsCount - 1);
var lastItemInGroup = false;
var targetGroup = dropInfo.TargetGroup;
if (targetGroup != null && targetGroup.IsBottomLevel && dropInfo.InsertPosition.HasFlag(RelativeInsertPosition.AfterTargetItem))
{
var indexOf = targetGroup.Items.IndexOf(dropInfo.TargetItem);
lastItemInGroup = indexOf == targetGroup.ItemCount - 1;
if (lastItemInGroup && dropInfo.InsertIndex != itemsCount)
{
index--;
}
}
var itemContainer = (UIElement)itemParent.ItemContainerGenerator.ContainerFromIndex(index);
var showAlwaysDropTargetAdorner = itemContainer == null && DragDrop.GetShowAlwaysDropTargetAdorner(itemParent);
if (showAlwaysDropTargetAdorner)
{
itemContainer = itemParent;
}
if (itemContainer != null)
{
var itemRect = new Rect(itemContainer.TranslatePoint(new Point(), AdornedElement), itemContainer.RenderSize);
Point point1,
point2;
double rotation = 0;
var viewportWidth = DropInfo.TargetScrollViewer?.ViewportWidth ?? double.MaxValue;
var viewportHeight = DropInfo.TargetScrollViewer?.ViewportHeight ?? double.MaxValue;
if (dropInfo.VisualTargetOrientation == Orientation.Vertical)
{
if ((dropInfo.InsertIndex == itemsCount) || lastItemInGroup)
{
if (itemsCount > 0)
{
itemRect.Y += itemContainer.RenderSize.Height;
}
else
{
if ((itemsControl as ListView)?.View is GridView)
{
var header = itemsControl.GetVisualDescendent <GridViewHeaderRowPresenter>();
if (header != null)
{
itemRect.Y += header.RenderSize.Height;
}
}
else if (itemsControl is DataGrid)
{
var header = itemsControl.GetVisualDescendent <DataGridColumnHeadersPresenter>();
if (header != null)
{
itemRect.Y += header.RenderSize.Height;
}
}
itemRect.Y += Pen.Thickness;
}
}
var itemRectRight = Math.Min(itemRect.Right, viewportWidth);
var itemRectLeft = itemRect.X < 0 ? 0 : itemRect.X;
point1 = new Point(itemRectLeft, itemRect.Y);
point2 = new Point(itemRectRight, itemRect.Y);
}
else
{
if (dropInfo.VisualTargetFlowDirection == FlowDirection.LeftToRight && dropInfo.InsertIndex == itemsCount)
{
if (itemsCount > 0)
{
itemRect.X += itemContainer.RenderSize.Width;
}
else
{
itemRect.X += Pen.Thickness;
}
}
else if (dropInfo.VisualTargetFlowDirection == FlowDirection.RightToLeft && dropInfo.InsertIndex != itemsCount)
{
if (itemsCount > 0)
{
itemRect.X += itemContainer.RenderSize.Width;
}
else
{
itemRect.X += Pen.Thickness;
}
}
var itemRectTop = itemRect.Y < 0 ? 0 : itemRect.Y;
var itemRectBottom = Math.Min(itemRect.Bottom, viewportHeight);
point1 = new Point(itemRect.X, itemRectTop);
point2 = new Point(itemRect.X, itemRectBottom);
rotation = 90;
}
drawingContext.DrawLine(Pen, point1, point2);
DrawTriangle(drawingContext, point1, rotation);
DrawTriangle(drawingContext, point2, 180 + rotation);
}
}
}
