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Asked: 2026-05-14T00:38:25+00:00

The Scene: A (smallish) Form hosting a UserControl. The Plot: Whenever UserControl raises a

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The Scene: A (smallish) Form hosting a UserControl.

The Plot: Whenever UserControl raises a hover event, display some (graphical) information in a tool tip fashion. When the user moves the mouse, fade them away again.

Notes: I’d like to display more than one “tooltip”, with each tooltip being a UserControl displaying information in a graphical manner. Not just text in a yellow box! Also, I’m using the Windows.Forms library.

This is what I have so far:

private void myControl_Hovered(object sender, MyEventArgs e)
{            
    var tooltip = new MyToolTip();
    Controls.Add(tooltip);
    tooltip.UpdateDisplay(e.Data);
    tooltip.Show();
}

But it shows up in the background (I can handle that) and, sadly, is confined to the window…

EDIT: Here is what I ended up doing…

I could not get the ToolTip control provided with .NET to work. This is mainly, because I’m trying to show tooltips for “hot spots” in a user drawn control (think a plot of function points, show additional items for the points). The ToolTip control would really like to only show when a user first enters a control – manually showing it does not seem to work. I tried. Long and hard.

So, this ToolTipWindow class can be used to show a control in a frameless window. I have added an Offset property, so it can be shown at an offset to the current mouse position.

/// <summary>
/// A tooltip class to display some information from a control.
/// </summary>
internal class ToolTipWindow: Form
{
    /// <summary>
    /// The offset from the mouse pointer to show the window at.
    /// </summary>
    public Point Offset { get; set;}

    internal ToolTipWindow(Control controlToDisplay)
    {
        FormBorderStyle = FormBorderStyle.None;
        TopMost = true;
        ShowInTaskbar = false;
        Opacity = 0.9;
        Width = controlToDisplay.Width;
        Height = controlToDisplay.Height;
        Controls.Add(controlToDisplay);
        controlToDisplay.Show();
    }

    /// <summary>
    /// Move the window to an offset of mouse pointer.
    /// </summary>
    protected override void OnShown(EventArgs e)
    {
        base.OnShown(e);
        Location = new Point(MousePosition.X + Offset.X, MousePosition.Y + Offset.Y);
    }

    /// <summary>
    /// Move the window to an offset of mouse pointer.
    /// </summary>
    protected override void OnVisibleChanged(EventArgs e)
    {
        base.OnVisibleChanged(e);
        if (Visible)
        {
            Location = new Point(MousePosition.X + Offset.X, MousePosition.Y +     Offset.Y);    
        }
    }
}

To show the tooltip, you can catch the MouseHover and MouseMove events. Check first, if you are above a “hot spot” and show the tooltip. In MouseMove, hide the tooltips if you are not above a “hot spot”. Also, on closing the window, make sure you also close all tooltip windows!

Note: The MouseHover event will only show up the first time the mouse enters a control. If you want it to show up repeatedly (as in the case of detecting “hot spots”), you should add code like the following to the control containing the “hot spots”:

    #region AddReHoverExperience
    // ReSharper disable InconsistentNaming
    // found this code here: http://www.pinvoke.net/default.aspx/user32.TrackMouseEvent

    [DllImport("user32.dll")]
    static extern int TrackMouseEvent(ref TRACKMOUSEEVENT lpEventTrack);
    [StructLayout(LayoutKind.Sequential)]

    public struct TRACKMOUSEEVENT

    {
        public UInt32 cbSize;
        public UInt32 dwFlags;
        public IntPtr hwndTrack;
        public UInt32 dwHoverTime;
    }

    TRACKMOUSEEVENT tme;
    private const uint TME_HOVER = 0x1;

    protected override void OnMouseHover(EventArgs e)
    {            
        base.OnMouseHover(e);
        OnMouseEnter(e);
    }

    protected override void OnMouseEnter(EventArgs e)
    {
        base.OnMouseEnter(e);
        tme = new TRACKMOUSEEVENT
                  {
                      hwndTrack = Handle, 
                      dwFlags = TME_HOVER, 
                      dwHoverTime = 500
                  };
        tme.cbSize = (uint)Marshal.SizeOf(tme);
        TrackMouseEvent(ref tme);
    }
    // ReSharper restore InconsistentNaming
    #endregion AddReHoverExperience
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1 Answer

  1. Editorial Team

    Your code has a serious problem, it adds a control to the user control every time the mouse hovers but never removes them.

    First, make very sure that the built-in ToolTip component doesn’t already solve your problem. It should, it behaves the way your describe. Note that it has the OwnerDraw property, it allows you to customize its appearance.

    Creating your own is tricky. A tool tip is a fairly unusual window, it isn’t a child control like all other WF controls. It is a top-level window, which allows it to overlap other windows and extend past the client area of the container window. The only class in Windows Forms that behaves this way is the Form class. Using a borderless form to implement your custom tool tip is possible.

    The trickiest part is ensuring that it moves when the parent form of your user control moves. You’ll have to iterate the Parent property of the UC until you find a Form, then subscribe the LocationChanged, VisibleChanged and FormClosing events. You’ll also should wire the UC’s ParentChanged and HandleDestroyed events.

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