请问有关:鼠标右键弹出菜单问题!

Question

我用以下的程序运行的结果是：当我在表头中按下鼠标右键时弹出菜单。
而我是想在某条记录的某个字段中按下鼠标右键时，弹出菜单；请问
各位大虾，该怎么改？谢谢！procedure TfrmMain.DBGrid1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var
    clientpoint,screenpoint:Tpoint;begin
    if button=mbright then
    begin
       clientpoint.x:=x;
       clientpoint.y:=y;
       screenpoint:=dbgrid1.ClientToScreen(clientpoint);
       inc(clickcount);
       if odd(clickcount) then
          popupmenu2.Popup(screenpoint.x,screenpoint.y);
       end;
end;