清空 TDateTimePicker 日期值的處理方式

procedure TForm1.DateTimePicker1KeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  if Key=VK_DELETE then
    DateTimePicker1.Format:=' ';
end;

procedure TForm1.DateTimePicker1Change(Sender: TObject);
begin
  DateTimePicker1.Format:=ShortDateFormat;
end;


在取用TDateTimePicker時，需檢查Format決定是空值還是日期值