高手来帮我看看这段代码

<P>rivate Sub Command1_Click()<BR>       <BR>     Dim pActiveView As IActiveView<BR>     Dim pExtentStack As IExtentStack<BR>   <BR>     If MapControl1.Map Is Nothing Then Exit Sub<BR>     <BR>     <BR>     <BR>     Set pActiveView = MapControl1.Map<BR>     <BR>     Set pExtentStack = pActiveView.ExtentStack<BR>    If pExtentStack.CanRedo = True Then<BR>    <BR>     pExtentStack.CanRedo<BR> <BR>   <BR>  End If<BR>End Sub</P>
<P>Private Sub Command2_Click()<BR>   <BR>     Dim pActiveView As IActiveView<BR>     Dim pExtentStack As IExtentStack<BR>   <BR>     If MapControl1.Map Is Nothing Then Exit Sub<BR>     <BR>     Set pActiveView = MapControl1.Map<BR>     <BR>     Set pExtentStack = pActiveView.ExtentStack<BR>    If pExtentStack.CanUndo Then<BR> <BR>     pExtentStack.CanUndo<BR>     <BR>  End If</P>
<P>End Sub</P>
<P>本意是想实现前进和后退两个功能的  可就是不行 我已经弄了好久了  痛苦呀~~~~~~~~</P>