Author: Tomas Rutkauskas

I'm trying to make a component that acts in certain cases like a combobox, i.e. 
when the user presses a button, a list box is shown and the user can select an 
item. The problem I have is that I need the list to hide itself whenever the user 
clicks the mouse outside the list (including clicks in non-windowed controls).

Answer:

One way you can do this is by listening for CM_CANCELMODE messages in the parent of 
your drop-down list (presumably an edit control or something similar). You will 
probably then have to work out whether the message originated from a click on the 
drop-down list or elsewhere. In the code below, FPopup points to the list component:
1   
2   procedure TMyPopupEdit.CMCancelMode(var message: TCMCancelMode);
3   var
4     P: TPoint;
5     R: TRect;
6   begin
7     {Get the top-left coordinate of the Sender and see if it is within the popup
8     control. If not, close the popup without changing the text in the edit box.}
9     P.X := message.Sender.Left;
10    P.Y := message.Sender.Top;
11    R := Rect(0, 0, FPopup.Width, FPopup.Height);
12    if not PtInRect(R, P) then
13      if FPopupVisible then
14        PopupCloseUp(FPopup, False);
15  end;