在ao的帮助里有个Cut polygons sample，你可以看看
Description:
This sample duplicates the 'Cut Polygon Features' task but uses a polygon edit sketch instead of a polyline edit sketch. This task makes it easier to create doughnut polygons for example. The illustration below shows an edit sketch being drawn over a single selected feature. Finishing the sketch creates a new feature by cutting it out from the selected feature.
'This task sets the edit sketch geometry to polygon type and uses this
'geometry as a cookie cutter on selected features
Option Explicit
Implements IEditTask
Private m_pEditor As IEditor
Private m_pEdSketch As IEditSketch
Private m_pMxDoc As IMxDocument
Private WithEvents EditorEvents As Editor
Private Sub IEditTask_Activate(ByVal Editor As esriEditor.IEditor, ByVal oldTask As esriEditor.IEditTask)
Set m_pEditor = Editor
Set EditorEvents = Editor
Set m_pEdSketch = Editor
Set m_pMxDoc = Editor.Parent.Document
'Call Selection changed to see if the sketch tools should be enabled
EditorEvents_OnSelectionChanged
End Sub
Private Sub IEditTask_Deactivate()
'When the task is deactivated, stop listening for events
Set EditorEvents = Nothing
End Sub
Private Property Get IEditTask_Name() As String
IEditTask_Name = "Cut Polygons by Area" 'Give our task a name
End Property
Private Sub IEditTask_OnDeleteSketch()
End Sub
Private Sub IEditTask_OnFinishSketch()
On Error GoTo handler:
Dim pRefreshArea As IInvalidArea 'Used to specify the area of the display to refresh
Dim pOrigFeature As IFeature 'The selected feature
Dim pNewFeature As IFeature 'New feature created during operation
Dim pEnumFeat As IEnumFeature
Dim pCutGeom As IGeometry 'The geometry that performs the cut - edit sketch
Dim pRemainder As IGeometry 'Difference between edit sketch and orig feature (modified orig feature)
Dim pSubDivision As IGeometry 'Intersection between edit sketch and orig feaure (new feature)
Dim pFeatureClass As IFeatureClass 'The feature class in which to place new features
Dim pTopoOperator As ITopologicalOperator
Dim pFields As IFields
Dim pField As IField
Dim FieldCount As Integer
'Start an edit operation so we can have undo/redo
m_pEditor.StartOperation
'Get ready to invalidate the features
Set pRefreshArea = New InvalidArea
Set pCutGeom = m_pEdSketch.Geometry 'Get the cutting geometry from the edit sketch
Set pTopoOperator = pCutGeom
pTopoOperator.Simplify ' make sure the edit sketch geometry is simple
Set pEnumFeat = m_pEditor.EditSelection 'Get the selected set of editable features
pEnumFeat.Reset
Set pOrigFeature = pEnumFeat.Next 'Get the next feature in the enumeration (the first one in this case)
If pOrigFeature Is Nothing Then GoTo handler 'abort the operation if nothing is selected
'Start a loop for each feature in the selection
Do While Not pOrigFeature Is Nothing
'Only process polygon features
If pOrigFeature.Shape.GeometryType = esriGeometryPolygon Then
pRefreshArea.Add pOrigFeature 'Add the feature to the invalidate object
Set pTopoOperator = pOrigFeature.Shape
Set pSubDivision = pTopoOperator.Intersect(pCutGeom, esriGeometry2Dimension)
If Not pSubDivision.IsEmpty Then
Set pFeatureClass = pOrigFeature.Class
Set pNewFeature = pFeatureClass.CreateFeature 'Create a new Feature in the same feature class
Set pNewFeature.Shape = pSubDivision 'Put the subdivided portion into this feature
'Set the original featuer's shape to the results returned from the difference
Set pRemainder = pTopoOperator.Difference(pCutGeom)
Set pOrigFeature.Shape = pRemainder
'copy the attributes of the orig feature the new feature
Set pFields = pOrigFeature.Fields
For FieldCount = 0 To pFields.FieldCount - 1 'skip OID and geometry
Set pField = pOrigFeature.Fields.Field(FieldCount)
If Not pField.Type = esriFieldTypeGeometry And Not pField.Type = esriFieldTypeOID _
And pField.Editable Then
pNewFeature.Value(FieldCount) = pOrigFeature.Value(FieldCount)
End If
Next FieldCount
pOrigFeature.Store 'Now store the original feature with the remainder geometry
pNewFeature.Store 'Store the subdivided feature
End If
End If 'End check for polygons
Set pOrigFeature = pEnumFeat.Next 'Get the next feature in the selection
Loop
m_pMxDoc.FocusMap.ClearSelection 'Clear the map's selection
'Refresh the display
Set pRefreshArea.Display = m_pEditor.Display
pRefreshArea.Invalidate esriAllScreenCaches 'Update the display
m_pEditor.StopOperation ("Cut Polygon Features") 'Complete the edit operation
Exit Sub
handler:
MsgBox "Unable to perform the cut task."
m_pEditor.AbortOperation 'In the event of an error, abort the operation
End Sub
Private Sub EditorEvents_OnSelectionChanged()
'Only enabled the sketch tools if there is something selected
If m_pEditor.SelectionCount = 0 Then
m_pEdSketch.GeometryType = esriGeometryNull
Else
m_pEdSketch.GeometryType = esriGeometryPolygon 'Set the edit sketch geometry type
End If
End Sub
