ToolTip.Popup event not firing with ToolTip.Show() in .NET Framework

Question

I have an old WinForms application with a normal TreeView, where I need to show customized tooltips for individual nodes.

I am using a ToolTip component (OwnerDraw=true and IsBalloon=false), and I show the tooltip programmatically with ToolTip.Show() from the MouseMove event of the TreeView. The Popup event handler (correctly) calculates and sets the tooltip size, and the Draw event handler (correctly) draws the tooltip.

My problem is that the Popup event does not fire - only the Draw event, resulting in that the displayed tooltip is much too small for the contents (I need to use a large fixed-width font: Consolas, 12).

I have already asked a question about this, thinking that I was doing something wrong, but I have now found that this works fine (for me) with .NET 8, but not with .NET Framework. I have tested .NET Framework 4.8 (which is what I have to use), 4.7.2, and 4.6.2 - the Popup event is not triggered with any of them.

From the .NET documentation on the ToolTip.Popup event (this is for 4.6.2, but it is the same for the others):

The Popup event is raised whenever a ToolTip is displayed, either through an explicit call to one of the Show methods or when the ToolTip class implicitly displays a ToolTip.

That part about it being raised for "an explicit call to one of the Show methods" does not seem to be true, or am I missing something?

I am not allowed to show my source code, but in his answer to my previous question, @Olivier Jacot-Descombes included the following code, which is very much like how I am doing it, and this is also the code I have been using for my tests since then:

public partial class FormTreeNodeToolTip : Form
{
    private static readonly Font _font = new Font("Consolas", 16, FontStyle.Regular);
    private TreeNode _currentNode;

    public FormTreeNodeToolTip()
    {
        InitializeComponent();

        treeView1.Nodes.Add(new TreeNode("First node"));
        treeView1.Nodes.Add(new TreeNode("Second node with longer text"));
        treeView1.Nodes.Add(new TreeNode("Third node"));
    }

    private void ToolTip1_Draw(object sender, DrawToolTipEventArgs e)
    {
        e.Graphics.Clear(Color.LightYellow);
        e.Graphics.DrawString(e.ToolTipText, _font, Brushes.Blue, e.Bounds);
    }

    private void TreeView1_NodeMouseHover(object sender, TreeNodeMouseHoverEventArgs e)
    {
        _currentNode = e.Node;
        Point cursor = treeView1.PointToClient(Cursor.Position);
        toolTip1.Show(e.Node.Text, treeView1, cursor.X + 20, cursor.Y + 20, 800);
    }

    private void ToolTip1_Popup(object sender, PopupEventArgs e)
    {
        e.ToolTipSize = TextRenderer.MeasureText(_currentNode.Text, _font);
    }

    private void TreeView1_MouseMove(object sender, MouseEventArgs e)
    {
        if (treeView1.GetNodeAt(e.Location) != _currentNode) {
            _currentNode = null;
            toolTip1.Hide(treeView1);
        }
    }

    private void TreeView1_MouseLeave(object sender, EventArgs e)
    {
        toolTip1.Hide(treeView1);
    }
}

I should add that I have tried using different events for showing the tooltip, setting ToolTip.Active to false and back to true when hiding/showing a tooltip, actively removing the "old" tooltip with ToolTip.SetToolTip() and ToolTip.RemoveAll(), and similar. Nothing I do makes any difference - the Popup event still does not fire.

So, is this a bug in .NET Framework, or am I missing something? What (if anything) can I do to make this work?

UPDATE 1:

Adding the form's designer code on request:

private void InitializeComponent()
{
    this.components = new System.ComponentModel.Container();
    this.toolTip1 = new System.Windows.Forms.ToolTip(this.components);
    this.treeView1 = new System.Windows.Forms.TreeView();
    this.SuspendLayout();
    // 
    // toolTip1
    // 
    this.toolTip1.OwnerDraw = true;
    this.toolTip1.Draw += new System.Windows.Forms.DrawToolTipEventHandler(this.ToolTip1_Draw);
    this.toolTip1.Popup += new System.Windows.Forms.PopupEventHandler(this.ToolTip1_Popup);
    // 
    // treeView1
    // 
    this.treeView1.Location = new System.Drawing.Point(0, 0);
    this.treeView1.Name = "treeView1";
    this.treeView1.Size = new System.Drawing.Size(306, 231);
    this.treeView1.TabIndex = 0;
    this.treeView1.NodeMouseHover += new System.Windows.Forms.TreeNodeMouseHoverEventHandler(this.TreeView1_NodeMouseHover);
    this.treeView1.MouseLeave += new System.EventHandler(this.TreeView1_MouseLeave);
    this.treeView1.MouseMove += new System.Windows.Forms.MouseEventHandler(this.TreeView1_MouseMove);
    // 
    // Form1
    // 
    this.AutoScaleDimensions = new System.Drawing.SizeF(9F, 20F);
    this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
    this.ClientSize = new System.Drawing.Size(710, 304);
    this.Controls.Add(this.treeView1);
    this.Name = "Form1";
    this.Text = "Form1";
    this.ResumeLayout(false);

}

UPDATE 2:

Added a few lines to the constructor in the example to add a couple of nodes in the TreeView. I did not think to mention that this simple example just shows the node's caption as tooltip, so the longer the caption string, the more obvious it becomes that the tooltip has an incorrect size.

Clarification:

This is not how the actual application works. There, the multi-line tooltip text for a node is decided based on other stuff, and needs to be assembled at the moment it is displayed.

It must also be displayed with a fixed-width font (we use Consolas 12, the example uses Consolas 16 to make the problem more visible even with short tooltips).

What does the subscription code look like (from the generated designer file)? — Matthew Watson
– Matthew Watson, Commented Aug 15 at 7:45
@MatthewWatson, added the whole InitializeComponent() method to the question now - it is not that big. — Boise
– Boise, Commented Aug 15 at 8:42
I cannot reproduce this with a simple form - I have the tooltip set to owner-draw and the tooltip appears after the ToolTip1_Popup() method is called. (Note that I am running it on .NET 4.8 but using an SDK-style project, not a legacy-style project.) — Matthew Watson
– Matthew Watson, Commented Aug 15 at 10:20
So does it work OK for you when you just have a Form with no other components and you subscribe to Form1_MouseHover to show the tooltip? — Matthew Watson
– Matthew Watson, Commented Aug 15 at 10:27
@MatthewWatson, I did not get around to testing your suggestion before I saw Solution 2 from shingo which solved my problem. But thank yo anyway! — Boise
– Boise, Commented Aug 16 at 7:38

shingo · Accepted Answer · 2025-08-15 14:42:18Z

5

Solution 1

TreeView natively supports showing tooltip, see TreeView.ShowNodeToolTips and TreeNode.ToolTipText, so you don't need to use an additional tooltip control.

Reason

This may be a bug*, but it was fixed by this PR anyway:

Before: ((tvhip.flags & TVHT.ONITEM) != 0)

After: tvhip.flags.HasFlag(TVHT.ONITEM)

When you show the tooltip, a WM_NOTIFY+TTN_SHOW message will be sent to the TreeView control first. Due to its ability to show tooltip on its own, a method called WmShowToolTip within the TreeView class will also handle this message. The original intention of this method is to detect the flag TVHT_ONITEM (0x46), but the previous code resulted in the flag TVHT_ONITEMLABEL (0x4) also being considered successful. As a result, the message is processed by the TreeView control, so tooltip fails to trigger the Popup event.

*The intention of the WmShowToolTip method may be to move external the tooltip to the top when the user manually shows them on the TreeView to prevent them from being obscured. If that's the case, perhaps it's not a bug and the current one is.

Solution 2

As explained above, in order to pass this message down, you need to rewrite the default WndProc method:

public class MyTreeView : TreeView
{
    protected override void WndProc(ref Message m)
    {
        const int WM_NOTIFY = 0x4e;
        const int WM_REFLECT = 0x2000;
        const int TTN_SHOW = -521;

        if (m.Msg == WM_NOTIFY)
        {
            var nmhdr = (NMHDR)m.GetLParam(typeof(NMHDR));
            if (nmhdr.code == TTN_SHOW)
            {
                m.Result = SendMessage(nmhdr.hwndFrom, WM_REFLECT + WM_NOTIFY, m.WParam, m.LParam);
                return;
            }
        }

        base.WndProc(ref m);
    }

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    private static extern IntPtr SendMessage(IntPtr hwnd, int msg, IntPtr wparam, IntPtr lparam);

    struct NMHDR
    {
        public IntPtr hwndFrom;
        public IntPtr idFrom;
        public int code;
    }
}

Solution 3

Since this issue only exists in the TreeView control, you can choose to show the tooltip on another control. E.G. you can place the treeview in a panel or UserControl (and set Dock = Fill), and then:

toolTip1.Show(e.Node.Text, panel1, cursor.X + 20, cursor.Y + 20, 800);

edited Aug 15 at 14:42

answered Aug 15 at 11:23

shingo

29.8k7 gold badges37 silver badges70 bronze badges

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3 Comments

Boise Aug 15 at 12:57

I am aware that the TreeView can show tooltips for nodes, but as I expressed in the question, I need to customize the tooltip. That is, the built-in node tooltip is unfortunately not good enough. Very interesting explanation (even if it does not help me) - thankyou!

shingo Aug 15 at 14:43

Added 2 solutions.

Boise Aug 16 at 7:11

Wow - thankyou! Your Solution 2 is just what I needed: Fixing the actual issue of the TreeView control by subclassing it, makes more sense to me than showing the tooltip on a "dummy" control and then having to explain that workaround. Thanks again, @shingo!

dr.null · Accepted Answer · 2025-09-08 06:24:23Z

You need to disable the built-in ToolTip to prevent processing its messages. This is necessary to prevent the TreeView from forcing the built-in ToolTip to display the clipped labels for example. This requires adding the TVS_NOTOOLTIPS style to the TreeView styles.

To show, hide, and calculate the size of the ToolTip window correctly, as shingo suggested in his answer (Solution 3), use the parent control of the TreeView as the associated control with the custom ToolTip.

While handling the TreeView mouse move, and to make the ToolTip popups less annoying, call the TreeView.HitTest method instead of the TreeView.GetNodeAt method to display the ToolTip only when the cursor is over the TreeViewHitTestLocations.Label portion of a TreeNode. Also, you might want to avoid showing the ToolTip when moving the cursor fast over the labels. You can achieve that by comparing the nodes of two TreeViewHitTestInfo calls separated by a delay task. A hit-test info of the e.Location before the delay, and another of the translated Cursor.Position after.

Use the TextRenderer To measure and draw strings on windows. Don't measure with Gdi and draw with Gdi+ as the OP shows. Different tools and different results.

Here's a working example.

[DesignerCategory("code")]
public class TreeViewEx : TreeView
{
    private readonly ToolTip toolTip;
    private TreeNode toolTipNode;
    private readonly Font toolTipFont;
    private readonly TextFormatFlags flags =
        TextFormatFlags.Default | 
        TextFormatFlags.WordBreak;        

    protected override CreateParams CreateParams
    {
        get
        {
            const int TVS_NOTOOLTIPS = 0x80;
            var pm = base.CreateParams;
            pm.Style |= TVS_NOTOOLTIPS;
            return pm;
        }
    }

    public TreeViewEx()
    {
        toolTipFont = new Font("Consolas", 16, FontStyle.Regular);
        toolTip = new ToolTip()
        {
            OwnerDraw = true,
            BackColor = Color.LightYellow,
        };
        toolTip.Popup += HandleToolTipPopup;
        toolTip.Draw += HandleToolTipDraw;
    }

    protected override void Dispose(bool disposing)
    {
        if (disposing)
        {
            toolTip.Dispose();
            toolTipFont.Dispose();
        }
        base.Dispose(disposing);
    }

    protected override async void OnMouseMove(MouseEventArgs e)
    {
        base.OnMouseMove(e);
        TreeViewHitTestInfo ht1 = HitTest(e.Location);
        await Task.Delay(500);
        TreeViewHitTestInfo ht2 = HitTest(PointToClient(Cursor.Position));

        if (ht1.Node == ht2.Node &&
            ht2.Location == TreeViewHitTestLocations.Label)                
        {
            if (ht2.Node != toolTipNode)
            {
                toolTipNode = ht2.Node;
                Point pos = PointToClient(Cursor.Position);
                pos.X += Cursor.Size.Width;
                pos.Y += Cursor.Size.Height * 2;
                toolTip.Show(toolTipNode.Text, Parent, pos);
            }
        }
        else
        {
            toolTipNode = null;
            toolTip.Hide(Parent);
        }
    }

    protected override void OnMouseLeave(EventArgs e)
    {
        base.OnMouseLeave(e);
        toolTipNode = null;
        toolTip.Hide(Parent);
    }

    private void HandleToolTipPopup(object sender, PopupEventArgs e)
    {
        if (toolTipNode != null)
        {
            using (var g = e.AssociatedControl.CreateGraphics())
            {
                e.ToolTipSize = TextRenderer.MeasureText(
                    g,
                    toolTipNode.Text,
                    toolTipFont,
                    e.AssociatedControl.Size,
                    flags);                    
            }
        }
    }

    private void HandleToolTipDraw(object sender, DrawToolTipEventArgs e)
    {
        e.DrawBackground();
        e.DrawBorder();
        TextRenderer.DrawText(
            e.Graphics, 
            e.ToolTipText, 
            toolTipFont, 
            e.Bounds, 
            Color.Blue, 
            flags);
    }
}

If the custom TreeView is not an option for some reason, you need to move the code to the corresponding handlers in your Form and do the necessary changes. Everything remains the same except adding the TVS_NOTOOLTIPS style part. You need to override the Form.OnHandleCreated method, p/invoke the GetWindowLongPtr and SetWindowLongPtr methods like this.

public partial class SomeForm : Form
{
    protected override void OnHandleCreated(EventArgs e)
    {
        base.OnHandleCreated(e);
        var style = GetWindowLongPtr(treeView1.Handle, GWL_STYLE).ToInt32();
        style |= TVS_NOTOOLTIPS;
        SetWindowLongPtr(treeView1.Handle, GWL_STYLE, new IntPtr(style));
    }

    const int GWL_STYLE = -16;
    const int TVS_NOTOOLTIPS = 0x80;

    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr GetWindowLongPtr(IntPtr hWnd, int nIndex);

    [DllImport("user32.dll", SetLastError = true)]
    static extern IntPtr SetWindowLongPtr(IntPtr hWnd, int nIndex, IntPtr dwNewLong);
}

Thank you dr.null for this very detailed answer! I decided to use Solution 2 in the answer from shingo, but this is excellent stuff to read for anyone struggling with similar problems. And your comments on the demo code are great, but that was just a minimal example to demonstrate the problem. The "real" code does not have those issues.

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