如何用代码设置图层在特定比例尺下显示？（急）

如题

<P>Option Explicit</P><P>Implements ICommand
Implements ICommandSubType</P><P>Private m_pHookHelper As IHookHelper
Private m_pMapControl As IMapControl3
Private m_lSubType As Long</P><P>Private Sub Class_Initialize()
  
  Set m_pHookHelper = New HookHelper
  
End Sub</P><P>Private Sub Class_Terminate()
  
  Set m_pHookHelper = Nothing
  
End Sub</P><P>Private Property Get ICommand_Enabled() As Boolean
  
  Dim bEnabled As Boolean
  bEnabled = True</P><P>  Dim pLayer As ILayer
  Set pLayer = m_pMapControl.CustomProperty</P><P>  If (m_lSubType = 3) Then
    If (pLayer.MaximumScale = 0) And (pLayer.MinimumScale = 0) Then bEnabled = False
  End If
  
  ICommand_Enabled = bEnabled
  
End Property
 
Private Property Get ICommand_Checked() As Boolean
  
  ICommand_Checked = False
  
End Property
 
Private Property Get ICommand_Name() As String
  
  ICommand_Name = "ScaleThresholds"
  
End Property</P><P>Private Property Get ICommand_Caption() As String
  
  If (m_lSubType = 1) Then
    ICommand_Caption = "Set Maximum Scale"
  ElseIf (m_lSubType = 2) Then
    ICommand_Caption = "Set Minimum Scale"
  Else
    ICommand_Caption = "Remove Scale Thresholds"
  End If</P><P>End Property
 
Private Property Get ICommand_Tooltip() As String
  
  'Not implemented
  
End Property
 
Private Property Get ICommand_Message() As String
  
  'Not implemented
  
End Property
 
Private Property Get ICommand_HelpFile() As String
  
  'Not implemented
  
End Property
 
Private Property Get ICommand_HelpContextID() As Long
  
  'Not implemented
  
End Property
 
Private Property Get ICommand_Bitmap() As esriSystem.OLE_HANDLE
  
  'Not implemented</P><P>End Property
 
Private Property Get ICommand_Category() As String
  
  'Not implemented
  
End Property
 
Private Sub ICommand_OnCreate(ByVal hook As Object)</P><P>  Set m_pHookHelper.hook = hook
  Set m_pMapControl = m_pHookHelper.hook
  
End Sub
 
Private Sub ICommand_OnClick()
  
  Dim pLayer As ILayer
  Set pLayer = m_pMapControl.CustomProperty
  If (m_lSubType = 1) Then pLayer.MaximumScale = m_pMapControl.MapScale
  If (m_lSubType = 2) Then pLayer.MinimumScale = m_pMapControl.MapScale
  If (m_lSubType = 3) Then
    pLayer.MaximumScale = 0
    pLayer.MinimumScale = 0
  End If
  m_pMapControl.Refresh esriViewDrawPhase.esriViewGeography</P><P>End Sub</P><P>Private Sub ICommandSubType_SetSubType(ByVal SubType As Long)</P><P>  m_lSubType = SubType</P><P>End Sub</P><P>Private Function ICommandSubType_GetCount() As Long</P><P>  ICommandSubType_GetCount = 3</P><P>End Function</P>

<P>thanks</P><img src="images/post/smile/dvbbs/em01.gif" /><img src="images/post/smile/dvbbs/em02.gif" />