VB中怎么做窗口伸缩

就是一个窗口，放上一个按钮，
按一下，隐藏窗口的一半，再按一下，又显示出来成一个完整大小都窗口

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If Me.Height = 300 Then Me.Height = 600 Else Me.Height = 300

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if me.left=0 then
    me.left=-300
else
    me.left=0
endif

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VB code:
Dim a As Double

Private Sub Command1_Click()
If Command1.Caption = "收缩" Then
Form1.Height = a / 2
Command1.Caption = "伸展"
Exit Sub
End If
If Command1.Caption = "伸展" Then
Form1.Height = a
Command1.Caption = "收缩"
Exit Sub
End If
End Sub

Private Sub Form_Load()
a = Form1.Height
Command1.Caption = "收缩"
End Sub

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谢谢，但使用了都不是我要的效果。