How can I force a drop-down combo to drop its list down?
This is done by using a Windows message called CB_SHOWDROPDOWN.
I recommend that you look in the WinAPI help under messages to see what else you can do
with them.
The nice thing about messaging in Windows is that the calls are all handled through the
Windows API SendMessage routine, which requires four parameters:
- Parameters of SendMessage function
- Window Handle (can be an object handle)
- Message specifies the message to be sent (in our case, CB_SHOWDROPDOWN)
- wParam, a 16-bit message-dependent parameter
- lParam, a 32-bit message-dependent parameter (see WinHelp for specifics on what goes
into wParam and lParam)
The gist of this is that Windows messages are performed in a very standard way, so if
you haven't done them much, I encourage you to investigate ways to employ them in your
code.
To get a combo-box list to automatically drop down when you enter it, put the following
code into the OnEnter event:
procedure TForm1.ComboBox1Enter(Sender: TObject);
begin
SendMessage(ComboBox1.handle, CB_SHOWDROPDOWN, Integer(True), 0);
end;
Likewise, you can close the drop-down when you exit by putting the following code into
the OnExit event of the combo box:
procedure TForm1.ComboBox1Exit(Sender: TObject);
begin
SendMessage(ComboBox1.handle, CB_SHOWDROPDOWN, Integer(False), 0);
end;
This is probably how the Intuit guys did it with Quicken. So go for it!
Copyright © 1995, 1996, 1997 Brendan V. Delumpa All Rights
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