我在form1上有四个edit,输完后我想用下上箭头键进行上移下移？怎么办？

procedure TForm1.Edit1KeyDown(Sender: TObject; var Key: Word; 
Shift: TShiftState); 
begin 
if key=vk_down then perform(WM_NEXTDLGCTL,0,0) else 
if key=vk_up then perform(WM_NEXTDLGCTL,1,0); 
end;