Hello,

I'm implementing an undo/redo drop-down menu similar to the undo/redo
menus in VS.NET 2003. The idea is that when the drop-down arrow is
pressed, a floating ListBox control appears under the pressed button,
and disappears when the user chooses an action to undo or clicks
anywhere else in the form - meaning that when the ListBox is open, I
need to handle every MouseDown event on the form.

I tried attaching an event handler to the MouseDown event of the
ListBox and then setting ListBox.Capture = true, but unfortunately that
didn't do the trick (why I couldn't figure out). Mouse events were
raised for every control on the form that handles them, and my
ListBox.MouseDown handler was only called when the mouse was over the
list box - i.e., capture wasn't working. Next I tried P/invoking
SetCapture and ReleaseCapture, but with the same result (unless the
mouse button was still pressed, in which case ALL system mouse events
were captured - far from ideal).

After lots of searching I found a message on this group saying that
only in a MouseLeave event handler will Control.Capture = true actually
make any difference - that turned out to be true and I finally got
capture to work. The only problem was that since the ListBox first
appears when the cursor is still on the drop-down button, capture
wasn't set until the cursor was moved over and out of the ListBox.

I finally solved it by some ugly cursor position fiddling. I
(programmatically) move the cursor position over the ListBox and then
move it back. I'm sharing this here in case someone gets stuck on a
similar problem. Also, if anyone has a better solution I'd love to see
it.

// Called from the toolbar's ButtonDropDown event handler
private void OpenHistoryList(ToolBarButton button)
{
    // Get the entry list associated with this history button
    HistoryEntryList entryList = (HistoryEntryList) button.Tag;

    // Add the list to the form
    ListBox listbox = new ListBox();
    this.Controls.Add(listbox);

    // Retrieve sizes from the configuration file
    int width =
int.Parse(ConfigurationSettings.AppSettings["History.Width"]);
    int height =
int.Parse(ConfigurationSettings.AppSettings["History.Height"]);

    // Set the list coordinates
    listbox.Location = new Point(button.Rectangle.X, button.Rectangle.Y +
button.Rectangle.Height);
    listbox.Width = width;
    listbox.Height = height;

    // Add the action descriptions to the list
    foreach(HistoryEntry entry in entryList)
    {
        listbox.Items.Add(entry.Description);
    }

    listbox.BringToFront();
    listbox.Focus();
    listbox.MouseDown += new MouseEventHandler(CloseHistoryList);
    listbox.MouseLeave += new EventHandler(CaptureHistoryList);

    // Fiddle with mouse position to generate a MouseLeave event
automatically
    Point currentPos = Cursor.Position;
    Rectangle listCoords =
listbox.RectangleToScreen(listbox.ClientRectangle);
    Cursor.Position = new Point(listCoords.Left+1, listCoords.Top+1);
    Application.DoEvents();
    Cursor.Position = currentPos;
}

private void CloseHistoryList(object sender, MouseEventArgs e)
{
    // Get the listbox's coordinates
    ListBox listbox = (ListBox) sender;
    Rectangle listCoords =
listbox.RectangleToScreen(listbox.ClientRectangle);

    // Check whether the click was within the listbox's bounds
    if (
        e.X < listCoords.X || e.X > listCoords.X + listCoords.Width ||
        e.Y< listCoords.Y || e.Y > listCoords.Y + listCoords.Height
    )
    {
        // Remove the listbox from the form, release mouse capture and
dispose of the listbox
        this.Controls.Remove(listbox);
        listbox.Capture = false;
        listbox.Dispose();
    }

}

private void CaptureHistoryList(object sender, EventArgs e)
{
    ListBox listbox = (ListBox) sender;
    listbox.Capture = true;
}

Hope that's useful

-Doron