aistudio-wpf-diagram/gong-wpf-dragdrop/src/GongSolutions.WPF.DragDrop/DropTargetInsertionAdorner.cs

using System;
using System.Windows;
using System.Windows.Media;
using System.Windows.Controls;
using GongSolutions.Wpf.DragDrop.Utilities;
using System.Windows.Controls.Primitives;

namespace GongSolutions.Wpf.DragDrop
{
    public class DropTargetInsertionAdorner : DropTargetAdorner
    {
        [Obsolete("This constructor is obsolete and will be deleted in next major release.")]
        public DropTargetInsertionAdorner(UIElement adornedElement)
            : base(adornedElement, (DropInfo)null)
        {
        }

        public DropTargetInsertionAdorner(UIElement adornedElement, DropInfo dropInfo)
            : base(adornedElement, dropInfo)
        {
        }

        /// <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 = this.DropInfo;
            var itemsControl = dropInfo.VisualTarget as ItemsControl;

            if (itemsControl != null)
            {
                // 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.
                ItemsControl itemParent;

                var visualTargetItem = dropInfo.VisualTargetItem;
                if (visualTargetItem != null)
                {
                    itemParent = ItemsControl.ItemsControlFromItemContainer(visualTargetItem);
                }
                else
                {
                    itemParent = 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(), this.AdornedElement), itemContainer.RenderSize);
                    Point point1,
                          point2;
                    double rotation = 0;

                    // I really don't know why I did this
                    //
                    // var viewportWidth = double.MaxValue;
                    // var viewportHeight = double.MaxValue;
                    // if (DropInfo.TargetScrollViewer != null)
                    // {
                    //     if (DropInfo.TargetScrollViewer.ScrollableWidth != 0)
                    //     {
                    //         viewportWidth = DropInfo.TargetScrollViewer.ViewportWidth;
                    //     }
                    //
                    //     if (DropInfo.TargetScrollViewer.ScrollableHeight != 0)
                    //     {
                    //         viewportHeight = DropInfo.TargetScrollViewer.ViewportHeight;
                    //     }
                    // }

                    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 += this.Pen.Thickness;
                            }
                        }

                        var itemRectRight = itemRect.Right; //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 += this.Pen.Thickness;
                            }
                        }
                        else if (dropInfo.VisualTargetFlowDirection == FlowDirection.RightToLeft && dropInfo.InsertIndex != itemsCount)
                        {
                            if (itemsCount > 0)
                            {
                                itemRect.X += itemContainer.RenderSize.Width;
                            }
                            else
                            {
                                itemRect.X += this.Pen.Thickness;
                            }
                        }

                        var itemRectTop = itemRect.Y < 0 ? 0 : itemRect.Y;
                        var itemRectBottom = itemRect.Bottom; //Math.Min(itemRect.Bottom, viewportHeight);

                        point1 = new Point(itemRect.X, itemRectTop);
                        point2 = new Point(itemRect.X, itemRectBottom);
                        rotation = 90;
                    }

                    drawingContext.DrawLine(this.Pen, point1, point2);
                    this.DrawTriangle(drawingContext, point1, rotation);
                    this.DrawTriangle(drawingContext, point2, 180 + rotation);
                }
            }
        }

        private void DrawTriangle(DrawingContext drawingContext, Point origin, double rotation)
        {
            drawingContext.PushTransform(new TranslateTransform(origin.X, origin.Y));
            drawingContext.PushTransform(new RotateTransform(rotation));

            drawingContext.DrawGeometry(this.Pen.Brush, null, m_Triangle);

            drawingContext.Pop();
            drawingContext.Pop();
        }

        static DropTargetInsertionAdorner()
        {
            // Create the pen and triangle in a static constructor and freeze them to improve performance.
            const int triangleSize = 5;

            var firstLine = new LineSegment(new Point(0, -triangleSize), false);
            firstLine.Freeze();
            var secondLine = new LineSegment(new Point(0, triangleSize), false);
            secondLine.Freeze();

            var figure = new PathFigure { StartPoint = new Point(triangleSize, 0) };
            figure.Segments.Add(firstLine);
            figure.Segments.Add(secondLine);
            figure.Freeze();

            m_Triangle = new PathGeometry();
            m_Triangle.Figures.Add(figure);
            m_Triangle.Freeze();
        }

        private static readonly PathGeometry m_Triangle;
    }
}