为什么如下的程序不能让我的image动？请指点
void __fastcall TForm1::FormKeyDown(TObject *Sender, WORD &Key,
      TShiftState Shift)
{
    switch(Key)
    {
      case VK_UP:
        this->Image1->Top-=20;
        break;
      case VK_DOWN:
        this->Image1->Top+=20;
        break;
      case VK_LEFT:
        this->Image1->Left-=20;
        break;
      case VK_RIGHT:
        this->Image1->Left+=20;
        break;
   }
}