真的不會(編號:8684)

我建了個從image1陣列,是從0~17的,用來當做遊戲的子彈
imgSpirit是代表飛機,以下是部分程式碼........
Private Sub Form_KeyDown(KeyCode As Integer, Shift As Integer)
Select Case KeyCode
  Case vbKeySpace
   isdown = True
   isfire = True
   If isfire = True Then start = imgSpirit.Left + imgSpirit.Width / 2
    n = n + 1
   End Select
End Sub
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Private Sub tmrAni_Timer()
If isdown = True Then      '是否按了發射飛彈事件
    If isfire = True Then
      Image1.Item(n).Move start, imgSpirit.Top
      Image1.Item(n).Visible = True
      isfire = False
    End If
      isdown = False
End If

Image1.Item(n).Top = Image1.Item(n).Top - 2           

End Sub
請問該要加些什麼程式碼,才能使之前每個發射出去的飛彈都能
持續前進,多謝