aistudio-wpf-diagram/Others/gong-wpf-dragdrop/src/GongSolutions.WPF.DragDrop/Utilities/HitTestUtilities.cs

using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Controls.Primitives;

namespace GongSolutions.Wpf.DragDrop.Utilities
{
    public static class HitTestUtilities
    {
        public static bool HitTest4Type<T>(object sender, Point elementPosition)
            where T : UIElement
        {
            var uiElement = GetHitTestElement4Type<T>(sender, elementPosition);
            return uiElement != null && uiElement.Visibility == Visibility.Visible;
        }

        private static T GetHitTestElement4Type<T>(object sender, Point elementPosition)
            where T : UIElement
        {
            var visual = sender as Visual;
            if (visual == null)
            {
                return null;
            }
            var hit = VisualTreeHelper.HitTest(visual, elementPosition);
            if (hit == null)
            {
                return null;
            }
            var uiElement = hit.VisualHit.GetVisualAncestor<T>();
            return uiElement;
        }

        public static bool HitTest4GridViewColumnHeader(object sender, Point elementPosition)
        {
            if (sender is ListView)
            {
                // no drag&drop for column header
                var columnHeader = GetHitTestElement4Type<GridViewColumnHeader>(sender, elementPosition);
                if (columnHeader != null && (columnHeader.Role == GridViewColumnHeaderRole.Floating || columnHeader.Visibility == Visibility.Visible))
                {
                    return true;
                }
            }
            return false;
        }

        public static bool HitTest4DataGridTypes(object sender, Point elementPosition)
        {
            if (sender is DataGrid)
            {
                // no drag&drop for column header
                var columnHeader = GetHitTestElement4Type<DataGridColumnHeader>(sender, elementPosition);
                if (columnHeader != null && columnHeader.Visibility == Visibility.Visible)
                {
                    return true;
                }
                // no drag&drop for row header
                var rowHeader = GetHitTestElement4Type<DataGridRowHeader>(sender, elementPosition);
                if (rowHeader != null && rowHeader.Visibility == Visibility.Visible)
                {
                    // no drag&drop for row header gripper
                    var thumb = GetHitTestElement4Type<Thumb>(sender, elementPosition);
                    if (thumb != null)
                    {
                        return true;
                    }
                }
                // drag&drop only for data grid row
                var dataRow = GetHitTestElement4Type<DataGridRow>(sender, elementPosition);
                return dataRow == null || Equals(dataRow.DataContext, CollectionView.NewItemPlaceholder);
            }
            return false;
        }

        public static bool HitTest4DataGridTypesOnDragOver(object sender, Point elementPosition)
        {
            if (sender is DataGrid)
            {
                // no drag&drop on column header
                var columnHeader = GetHitTestElement4Type<DataGridColumnHeader>(sender, elementPosition);
                if (columnHeader != null && columnHeader.Visibility == Visibility.Visible)
                {
                    return true;
                }
            }
            return false;
        }

        /// <summary>
        /// thx to @osicka from issue #84
        /// 
        /// e.g. original source is part of a popup (e.g. ComboBox drop down), the hit test needs to be done on the original source.
        /// Because the popup is not attached to the visual tree of the sender.
        /// This function test this by looping back from the original source to the sender and if it didn't end up at the sender stopped the drag.
        /// </summary>
        public static bool IsNotPartOfSender(object sender, MouseButtonEventArgs e)
        {
            var visual = e.OriginalSource as Visual;
            if (visual == null)
            {
                return false;
            }
            var hit = VisualTreeHelper.HitTest(visual, e.GetPosition((IInputElement)visual));

            if (hit == null)
            {
                return false;
            }
            else
            {
                var depObj = e.OriginalSource as DependencyObject;
                if (depObj == null)
                {
                    return false;
                }
                if (depObj == sender)
                {
                    return false;
                }

                var item = VisualTreeHelper.GetParent(depObj.FindVisualTreeRoot());
                //var item = VisualTreeHelper.GetParent(e.OriginalSource as DependencyObject);

                while (item != null && item != sender)
                {
                    item = VisualTreeHelper.GetParent(item);
                }
                return item != sender;
            }
        }
    }
}