VB画图求助

我在窗体上隐藏了一个picturebox,事件驱动后，picturebox为可见，后再在picturebox里定义坐标系，接着用line画图为什么画不出来啊？
谢谢帮助

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picture1.line

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.auotredraw=true

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Private Sub Combo1_click()

Select Case Combo1.Text
Case "电机电压"
Picture2.Visible = True
Picture2.Scale (0, Picture2.ScaleHeight)-(Picture2.ScaleWidth, 0)
Picture2.Line (Picture2.ScaleWidth / 2, Picture2.ScaleHeight)-(Picture2.ScaleWidth / 2, 0), vbBlack
谢谢楼上回复
程序是这样的，像楼上说的改动后还是不能显示啊

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VB code:
Option Explicit

Private Sub Combo1_click()
Select Case Combo1.Text
Case "电机电压"
Picture2.Visible = True
Picture2.Scale (0, 0)-(Picture2.ScaleWidth, Picture2.ScaleHeight)
Picture2.Line (Picture2.ScaleWidth / 2, Picture2.ScaleHeight)-(Picture2.ScaleWidth / 2, 0), vbBlack
End Select
End Sub

Private Sub Form_Load()
Combo1.AddItem "电机电压"
Picture2.AutoRedraw = True
End Sub

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Picture2.AutoRedraw = True这一句是关键

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Picture2.Visible = True
Picture2.Scale (0, Picture2.ScaleHeight)-(Picture2.ScaleWidth, 0)
Picture2.Line (Picture2.ScaleWidth / 2, Picture2.ScaleHeight)-(Picture2.ScaleWidth / 2, 0), vbBlack
Picture2.Refresh '加这句试试

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Picture2.Scale调整的是picture绘图区左上坐标,和大小(比例,刻度)