arcengine 查询 Recyle参数测试
助中有如此论述，指出recycling参数的主要性：
TheRecyclingparameter controls feature object allocation behavior. Recycling cursors rehydrate a single feature object on each fetch and can be used to optimize read-only access, for example, when drawing. It is illegal to maintain a reference on a feature object returned by a recycling cursor across multiple calls to NextFeature on the cursor. Feature objects returned by a recycling cursor should not be modified.
Non-recycling cursors return a separate feature object on each fetch. The objects returned by a non-recycling cursor may be modified and stored with polymorphic behavior. The geodatabase guarantees 'unique instance semantics' on non-recycling feature objects fetched during an edit session.
Recycling cursors should be used only for drawing and read-only access to object state. Use non-recycling search cursors to fetch objects that are to be updated.
通过下面的函数可以测试该参数的重要性：
Const N = 100000
Sub TestRecycle()
Dim amap As IMxDocument
Set amap = ThisDocument
Dim lyr As IFeatureLayer
Set lyr = amap.FocusMap.Layer(0)
Dim fc As IFeatureCursor
Dim qr As IQueryFilter
Set qr = New QueryFilter
qr.WhereClause = "objectID < " & N
Dim dt As Date
Debug.Print "Recyle: False"
dt = Now
Set fc = lyr.Search(qr, False)
While Not fc.NextFeature Is Nothing
Wend
Debug.Print "Seconds: " & DateDiff("s", dt, Now)
dt = Now
Debug.Print "Recyle: True"
Set fc = lyr.Search(qr, True)
While Not fc.NextFeature Is Nothing
Wend
Debug.Print "Seconds: " & DateDiff("s", dt, Now)
End Sub
结果如下：
N=100000
Recyle: False
Seconds: 3
Recyle: True
Seconds: 1
N=500000
Recyle: False
Seconds: 12
Recyle: True
Seconds: 8
说明在只读查询中，将Recycling参数设为true可以提高函数效率。
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