Shrlalgo.RvKits/WPFDark/Internals/TreeViewHelper.cs

using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;

namespace WPFDark.Internals
{
    // https://stackoverflow.com/questions/1131161/how-can-i-make-wpf-trigger-for-ismouseover-on-treeviewitem-not-affect-all-parent
    internal static class TreeViewHelper
    {
        //
        // The TreeViewItem that the mouse is currently directly over (or null).
        //
        private static TreeViewItem? _currentItem;

        //
        // IsMouseDirectlyOverItem:  A DependencyProperty that will be true only on the 
        // TreeViewItem that the mouse is directly over.  I.e., this won't be set on that 
        // parent item.
        //
        // This is the only public member, and is read-only.
        //

        // The property key (since this is a read-only DP)
        private static readonly DependencyPropertyKey IsMouseDirectlyOverItemKey =
            DependencyProperty.RegisterAttachedReadOnly("IsMouseDirectlyOverItem",
                typeof(bool),
                typeof(TreeViewHelper),
                new FrameworkPropertyMetadata(null, CalculateIsMouseDirectlyOverItem));

        // The DP itself
        public static readonly DependencyProperty IsMouseDirectlyOverItemProperty =
            IsMouseDirectlyOverItemKey.DependencyProperty;

        // A strongly-typed getter for the property.
        public static bool GetIsMouseDirectlyOverItem(DependencyObject obj)
        {
            return (bool) obj.GetValue(IsMouseDirectlyOverItemProperty);
        }

        // A coercion method for the property
        private static object CalculateIsMouseDirectlyOverItem(DependencyObject item, object value)
        {
            // This method is called when the IsMouseDirectlyOver property is being calculated
            // for a TreeViewItem.  

            return item == _currentItem ? true : false;
        }

        //
        // UpdateOverItem:  A private RoutedEvent used to find the nearest encapsulating
        // TreeViewItem to the mouse's current position.
        //

        private static readonly RoutedEvent UpdateOverItemEvent = EventManager.RegisterRoutedEvent(
            "UpdateOverItem", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(TreeViewHelper));

        //
        // Class constructor
        //

        static TreeViewHelper()
        {
            // Get all Mouse enter/leave events for TreeViewItem.
            EventManager.RegisterClassHandler(typeof(TreeViewItem), UIElement.MouseEnterEvent,
                new MouseEventHandler(OnMouseTransition), true);
            EventManager.RegisterClassHandler(typeof(TreeViewItem), UIElement.MouseLeaveEvent,
                new MouseEventHandler(OnMouseTransition), true);

            // Listen for the UpdateOverItemEvent on all TreeViewItem's.
            EventManager.RegisterClassHandler(typeof(TreeViewItem), UpdateOverItemEvent,
                new RoutedEventHandler(OnUpdateOverItem));
        }


        //
        // OnUpdateOverItem:  This method is a listener for the UpdateOverItemEvent.  When it is received,
        // it means that the sender is the closest TreeViewItem to the mouse (closest in the sense of the tree,
        // not geographically).

        static void OnUpdateOverItem(object sender, RoutedEventArgs args)
        {
            // Mark this object as the tree view item over which the mouse
            // is currently positioned.
            _currentItem = sender as TreeViewItem;

            // Tell that item to re-calculate the IsMouseDirectlyOverItem property
            _currentItem?.InvalidateProperty(IsMouseDirectlyOverItemProperty);

            // Prevent this event from notifying other tree view items higher in the tree.
            args.Handled = true;
        }

        //
        // OnMouseTransition:  This method is a listener for both the MouseEnter event and
        // the MouseLeave event on TreeViewItems.  It updates the _currentItem, and updates
        // the IsMouseDirectlyOverItem property on the previous TreeViewItem and the new
        // TreeViewItem.

        static void OnMouseTransition(object sender, MouseEventArgs args)
        {
            lock (IsMouseDirectlyOverItemProperty)
            {
                if (_currentItem != null)
                {
                    // Tell the item that previously had the mouse that it no longer does.
                    DependencyObject oldItem = _currentItem;
                    _currentItem = null;
                    oldItem.InvalidateProperty(IsMouseDirectlyOverItemProperty);
                }

                // Get the element that is currently under the mouse.
                IInputElement currentPosition = Mouse.DirectlyOver;

                // See if the mouse is still over something (any element, not just a tree view item).
                if (currentPosition != null)
                {
                    // Yes, the mouse is over something.
                    // Raise an event from that point.  If a TreeViewItem is anywhere above this point
                    // in the tree, it will receive this event and update _currentItem.

                    RoutedEventArgs newItemArgs = new RoutedEventArgs(UpdateOverItemEvent);
                    currentPosition.RaiseEvent(newItemArgs);
                }
            }
        }
    }
}