IFeatureLayer Search函数参数测试

<P>帮助中有如此论述，指出recycling参数的主要性：</P>
<P>The <EM>Recycling</EM> parameter 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.</P>
<P>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.</P>
<P>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. </P>
<P><STRONG>通过下面的函数可以测试该参数的重要性：</STRONG></P>
<P><STRONG>Const N = 100000<BR></STRONG><STRONG></STRONG></P>
<P><STRONG>Sub TestRecycle()<BR>Dim amap As IMxDocument<BR>Set amap = ThisDocument</STRONG></P>
<P><STRONG>  Dim lyr As IFeatureLayer<BR>  Set lyr = amap.FocusMap.Layer(0)<BR>  Dim fc As IFeatureCursor<BR>  <BR>  Dim qr As IQueryFilter<BR>  Set qr = New QueryFilter<BR>  qr.WhereClause = "objectID < " ; N<BR>  Dim dt As Date<BR>  <BR>  Debug.Print "Recyle: False"<BR>  dt = Now<BR>  Set fc = lyr.Search(qr, False)<BR>  While Not fc.NextFeature Is Nothing<BR>  <BR>  Wend<BR>Debug.Print "Seconds: " ; DateDiff("s", dt, Now)<BR>  <BR>  dt = Now<BR>  Debug.Print "Recyle: True"<BR>  Set fc = lyr.Search(qr, True)<BR>  While Not fc.NextFeature Is Nothing<BR>  <BR>  Wend<BR>Debug.Print "Seconds: " ; DateDiff("s", dt, Now)<BR>  <BR>End Sub</STRONG></P>
<P><STRONG>结果如下：</STRONG></P>
<P><STRONG>N=100000</STRONG></P>
<P>Recyle: False<BR>Seconds: 3<BR>Recyle: True<BR>Seconds: 1</P>
<P><STRONG>N=500000</STRONG></P>
<P>Recyle: False<BR>Seconds: 12<BR>Recyle: True<BR>Seconds: 8</P>
<P>说明在只读查询中，将Recycling参数设为true可以提高函数效率。</P>