procedure TForm1.FormKeyDown(Sender: TObject;
var Key: Word;
Shift: TShiftState);
begin
if Key = 17 then
ShowMessage('是Ctrl键!');
end;
或者
procedure TForm1.FormKeyDown(Sender: TObject;
var Key: Word;
Shift: TShiftState);
begin
if Key = VK_CONTROL then
ShowMessage('是Ctrl键!');
end;