Support keyboard tooltips in TreeNode (#4466)

src/System.Windows.Forms/src/PublicAPI.Unshipped.txt

@@ -0,0 +1,2 @@
+~override System.Windows.Forms.TreeView.OnGotFocus(System.EventArgs e) -> void
+~override System.Windows.Forms.TreeView.OnLostFocus(System.EventArgs e) -> void

src/System.Windows.Forms/src/System/Windows/Forms/Control.cs

@@ -14061,6 +14061,9 @@ static bool IsKeyDown(Keys key, ReadOnlySpan<byte> stateArray)
             }
         }
 
+        internal virtual ComCtl32.ToolInfoWrapper<Control> GetToolInfoWrapper(ComCtl32.TTF flags, string caption, ToolTip tooltip)
+            => new ComCtl32.ToolInfoWrapper<Control>(this, flags, caption);
+
         private readonly WeakReference<ToolStripControlHost> toolStripControlHostReference
             = new WeakReference<ToolStripControlHost>(null);
 

src/System.Windows.Forms/src/System/Windows/Forms/ListView.cs

@@ -3503,6 +3503,17 @@ internal int GetNativeGroupId(ListViewItem item)
             }
         }
 
+        internal unsafe override ComCtl32.ToolInfoWrapper<Control> GetToolInfoWrapper(TTF flags, string caption, ToolTip tooltip)
+        {
+            // The "ShowItemToolTips" flag is required so that when the user hovers over the ListViewItem,
+            // their own tooltip is displayed, not the ListViewItem tooltip.
+            var wrapper = new ComCtl32.ToolInfoWrapper<Control>(this, flags, ShowItemToolTips ? null : caption);
+            if (ShowItemToolTips)
+                wrapper.Info.lpszText = (char*)(-1);
+
+            return wrapper;
+        }
+
         internal void GetSubItemAt(int x, int y, out int iItem, out int iSubItem)
         {
             var lvhi = new LVHITTESTINFO

src/System.Windows.Forms/src/System/Windows/Forms/ToolTip.cs

@@ -991,14 +991,7 @@ private unsafe ToolInfoWrapper<Control> GetTOOLINFO(Control control, string capt
                 flags |= TTF.RTLREADING;
             }
 
-            bool noText = (control is TreeView tv && tv.ShowNodeToolTips)
-                || (control is ListView lv && lv.ShowItemToolTips);
-
-            var info = new ToolInfoWrapper<Control>(control, flags, noText ? null : caption);
-            if (noText)
-                info.Info.lpszText = (char*)(-1);
-
-            return info;
+            return control.GetToolInfoWrapper(flags, caption, this);
         }
 
         private ToolInfoWrapper<IWin32WindowAdapter> GetWinTOOLINFO(IWin32Window hWnd)
@@ -1995,15 +1988,6 @@ private void WmMove()
                 return;
             }
 
-            // Treeview handles its own ToolTips.
-            if (window is TreeView treeView)
-            {
-                if (treeView.ShowNodeToolTips)
-                {
-                    return;
-                }
-            }
-
             // Reposition the tooltip when its about to be shown since the tooltip can go out of screen
             // working area bounds Reposition would check the bounds for us.
             var r = new RECT();

src/System.Windows.Forms/src/System/Windows/Forms/TreeNode.IKeyboardToolTip.cs

@@ -0,0 +1,66 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using System.Drawing;
+
+namespace System.Windows.Forms
+{
+    public partial class TreeNode : IKeyboardToolTip
+    {
+        bool IKeyboardToolTip.AllowsChildrenToShowToolTips() => AllowToolTips;
+
+        bool IKeyboardToolTip.AllowsToolTip() => true;
+
+        bool IKeyboardToolTip.CanShowToolTipsNow() => AllowToolTips;
+
+        string IKeyboardToolTip.GetCaptionForTool(ToolTip toolTip) => ToolTipText;
+
+        Rectangle IKeyboardToolTip.GetNativeScreenRectangle() => RectangleToScreen(Bounds);
+
+        IList<Rectangle> IKeyboardToolTip.GetNeighboringToolsRectangles()
+        {
+            TreeNode nextNode = NextVisibleNode;
+            TreeNode prevNode = PrevVisibleNode;
+            List<Rectangle> neighboringRectangles = new List<Rectangle>();
+
+            if (nextNode is not null)
+            {
+                neighboringRectangles.Add(RectangleToScreen(nextNode.Bounds));
+            }
+
+            if (prevNode is not null)
+            {
+                neighboringRectangles.Add(RectangleToScreen(prevNode.Bounds));
+            }
+
+            return neighboringRectangles;
+        }
+
+        IWin32Window IKeyboardToolTip.GetOwnerWindow() => TreeView;
+
+        bool IKeyboardToolTip.HasRtlModeEnabled() => TreeView?.RightToLeft == RightToLeft.Yes;
+
+        bool IKeyboardToolTip.IsBeingTabbedTo() => Control.AreCommonNavigationalKeysDown();
+
+        bool IKeyboardToolTip.IsHoveredWithMouse() => TreeView?.AccessibilityObject.Bounds.Contains(Control.MousePosition) ?? false;
+
+        void IKeyboardToolTip.OnHooked(ToolTip toolTip) => OnKeyboardToolTipHook(toolTip);
+
+        void IKeyboardToolTip.OnUnhooked(ToolTip toolTip) => OnKeyboardToolTipUnhook(toolTip);
+
+        bool IKeyboardToolTip.ShowsOwnToolTip() => AllowToolTips;
+
+        private bool AllowToolTips => TreeView?.ShowNodeToolTips ?? false;
+
+        internal virtual void OnKeyboardToolTipHook(ToolTip toolTip) { }
+
+        internal virtual void OnKeyboardToolTipUnhook(ToolTip toolTip) { }
+
+        private Rectangle RectangleToScreen(Rectangle bounds)
+        {
+            return TreeView?.RectangleToScreen(bounds) ?? Rectangle.Empty;
+        }
+    }
+}

src/System.Windows.Forms/src/System/Windows/Forms/TreeNode.cs

@@ -5,6 +5,7 @@
 #nullable disable
 
 using System.Collections;
+using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics;
 using System.Drawing;
@@ -24,7 +25,7 @@ namespace System.Windows.Forms
     [TypeConverterAttribute(typeof(TreeNodeConverter))]
     [Serializable]  // This class participates in resx serialization.
     [DefaultProperty(nameof(Text))]
-    public class TreeNode : MarshalByRefObject, ICloneable, ISerializable
+    public partial class TreeNode : MarshalByRefObject, ICloneable, ISerializable
     {
         internal const int SHIFTVAL = 12;
         private const TVIS CHECKED = (TVIS)(2 << SHIFTVAL);
@@ -1796,6 +1797,7 @@ public void ExpandAll()
                 children[i].ExpandAll();
             }
         }
+
         /// <summary>
         ///  Locate this tree node's containing tree view control by scanning
         ///  up to the virtual root, whose treeView pointer we know to be
@@ -1812,6 +1814,22 @@ internal TreeView FindTreeView()
             return node.treeView;
         }
 
+        internal List<TreeNode> GetSelfAndChildNodes()
+        {
+            List<TreeNode> nodes = new List<TreeNode>() { this };
+            AggregateChildNodesToList(this);
+            return nodes;
+
+            void AggregateChildNodesToList(TreeNode parentNode)
+            {
+                foreach (TreeNode child in parentNode.Nodes)
+                {
+                    nodes.Add(child);
+                    AggregateChildNodesToList(child);
+                }
+            }
+        }
+
         /// <summary>
         ///  Helper function for getFullPath().
         /// </summary>
@@ -2035,11 +2053,11 @@ internal void Remove(bool notify)
 
             // unlink our children
             //
-
             for (int i = 0; i < childCount; i++)
             {
                 children[i].Remove(false);
             }
+
             // children = null;
             // unlink ourself
             if (notify && parent != null)
@@ -2063,6 +2081,8 @@ internal void Remove(bool notify)
                 return;
             }
 
+            KeyboardToolTipStateMachine.Instance.Unhook(this, tv.KeyboardToolTip);
+
             if (handle != IntPtr.Zero)
             {
                 if (notify && tv.IsHandleCreated)
@@ -2287,9 +2307,6 @@ internal unsafe void UpdateImage()
         /// <summary>
         ///  ISerializable private implementation
         /// </summary>
-        void ISerializable.GetObjectData(SerializationInfo si, StreamingContext context)
-        {
-            Serialize(si, context);
-        }
+        void ISerializable.GetObjectData(SerializationInfo si, StreamingContext context) => Serialize(si, context);
     }
 }

src/System.Windows.Forms/src/System/Windows/Forms/TreeNodeCollection.cs

@@ -367,6 +367,15 @@ private int AddInternal(TreeNode node, int delta)
 
             // If the TreeView is sorted, index is ignored
             TreeView tv = owner.TreeView;
+
+            if (tv is not null)
+            {
+                foreach (TreeNode treeNode in node.GetSelfAndChildNodes())
+                {
+                    KeyboardToolTipStateMachine.Instance.Hook(treeNode, tv.KeyboardToolTip);
+                }
+            }
+
             if (tv != null && tv.Sorted)
             {
                 return owner.AddSorted(node);
@@ -516,6 +525,15 @@ public virtual void Insert(int index, TreeNode node)
 
             // If the TreeView is sorted, index is ignored
             TreeView tv = owner.TreeView;
+
+            if (tv is not null)
+            {
+                foreach (TreeNode treeNode in node.GetSelfAndChildNodes())
+                {
+                    KeyboardToolTipStateMachine.Instance.Hook(treeNode, tv.KeyboardToolTip);
+                }
+            }
+
             if (tv != null && tv.Sorted)
             {
                 owner.AddSorted(node);

src/System.Windows.Forms/src/System/Windows/Forms/TreeView.cs

@@ -5,6 +5,7 @@
 #nullable disable
 
 using System.Collections;
+using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics;
 using System.Drawing;
@@ -863,6 +864,8 @@ public int ItemHeight
             }
         }
 
+        internal ToolTip KeyboardToolTip { get; } = new ToolTip();
+
         /// <summary>
         ///  The LabelEdit property determines if the label text
         ///  of nodes in the tree view is editable.
@@ -1639,7 +1642,9 @@ protected override void Dispose(bool disposing)
             }
 
             // Dispose unmanaged resources.
+            UnhookNodes();
             _toolTipBuffer.Dispose();
+            KeyboardToolTip.Dispose();
 
             base.Dispose(disposing);
         }
@@ -1806,6 +1811,22 @@ private void ImageListChangedHandle(object sender, EventArgs e)
             }
         }
 
+        private void NotifyAboutGotFocus(TreeNode treeNode)
+        {
+            if (treeNode is not null)
+            {
+                KeyboardToolTipStateMachine.Instance.NotifyAboutGotFocus(treeNode);
+            }
+        }
+
+        private void NotifyAboutLostFocus(TreeNode treeNode)
+        {
+            if (treeNode is not null)
+            {
+                KeyboardToolTipStateMachine.Instance.NotifyAboutLostFocus(treeNode);
+            }
+        }
+
         private void StateImageListRecreateHandle(object sender, EventArgs e)
         {
             if (IsHandleCreated)
@@ -2130,6 +2151,7 @@ protected override void OnMouseHover(EventArgs e)
                 {
                     OnNodeMouseHover(new TreeNodeMouseHoverEventArgs(tn));
                     prevHoveredNode = tn;
+                    NotifyAboutLostFocus(SelectedNode);
                 }
             }
 
@@ -2508,6 +2530,7 @@ private unsafe IntPtr TvnSelecting(NMTREEVIEW* nmtv)
             {
                 case TVC.BYKEYBOARD:
                     action = TreeViewAction.ByKeyboard;
+                    NotifyAboutLostFocus(SelectedNode);
                     break;
                 case TVC.BYMOUSE:
                     action = TreeViewAction.ByMouse;
@@ -2530,18 +2553,20 @@ private unsafe void TvnSelected(NMTREEVIEW* nmtv)
 
             if (nmtv->itemNew.hItem != IntPtr.Zero)
             {
+                TreeNode node = NodeFromHandle(nmtv->itemNew.hItem);
                 TreeViewAction action = TreeViewAction.Unknown;
                 switch (nmtv->action)
                 {
                     case TVC.BYKEYBOARD:
                         action = TreeViewAction.ByKeyboard;
+                        NotifyAboutGotFocus(node);
                         break;
                     case TVC.BYMOUSE:
                         action = TreeViewAction.ByMouse;
                         break;
                 }
 
-                OnAfterSelect(new TreeViewEventArgs(NodeFromHandle(nmtv->itemNew.hItem), action));
+                OnAfterSelect(new TreeViewEventArgs(node, action));
             }
 
             // TreeView doesn't properly revert back to the unselected image
@@ -2862,6 +2887,20 @@ protected OwnerDrawPropertyBag GetItemRenderStyles(TreeNode node, int state)
             return retval;
         }
 
+        internal unsafe override ComCtl32.ToolInfoWrapper<Control> GetToolInfoWrapper(TTF flags, string caption, ToolTip tooltip)
+        {
+            // The "ShowNodeToolTips" flag is required so that when the user hovers over the TreeNode,
+            // their own tooltip is displayed, not the TreeView tooltip.
+            // The second condition is necessary for the correct display of the keyboard tooltip,
+            // since the logic of the external tooltip blocks its display
+            bool isExternalTooltip = ShowNodeToolTips && tooltip != KeyboardToolTip;
+            var wrapper = new ComCtl32.ToolInfoWrapper<Control>(this, flags, isExternalTooltip ? null : caption);
+            if (isExternalTooltip)
+                wrapper.Info.lpszText = (char*)(-1);
+
+            return wrapper;
+        }
+
         private unsafe bool WmShowToolTip(ref Message m)
         {
             User32.NMHDR* nmhdr = (User32.NMHDR*)m.LParam;
@@ -3034,6 +3073,18 @@ private unsafe void WmNotify(ref Message m)
             }
         }
 
+        protected override void OnGotFocus(EventArgs e)
+        {
+            base.OnGotFocus(e);
+            NotifyAboutGotFocus(SelectedNode);
+        }
+
+        protected override void OnLostFocus(EventArgs e)
+        {
+            base.OnLostFocus(e);
+            NotifyAboutLostFocus(SelectedNode);
+        }
+
         /// <summary>
         ///  Shows the context menu for the Treenode.
         /// </summary>
@@ -3059,6 +3110,17 @@ private void ContextMenuStripClosing(object sender, ToolStripDropDownClosingEven
             User32.SendMessageW(this, (User32.WM)TVM.SELECTITEM, (IntPtr)TVGN.DROPHILITE);
         }
 
+        private void UnhookNodes()
+        {
+            foreach (TreeNode rootNode in Nodes)
+            {
+                foreach (TreeNode node in rootNode.GetSelfAndChildNodes())
+                {
+                    KeyboardToolTipStateMachine.Instance.Unhook(node, KeyboardToolTip);
+                }
+            }
+        }
+
         private void WmPrint(ref Message m)
         {
             base.WndProc(ref m);