IFeatureClass的Search方法大家经常用到，很多人对Search方法的其中一个参数bool Recycling不是很理解。目前网上关于这个参数的意义的解释有两个版本：1.第一版本是IsNotNull大牛的：http://bbs.esrichina-bj.cn/ESRI/viewthread.php?tid=13461他提出的观点的是：参数Recycling为True的时候是传引用，为False的时候为传值2.第二个版本是Echo兄的：http://gis.cnblogs.com/home.aspx?page=3他提出的观点是：参数Recycling为True的时候游标对象(Ifeaturecursor)是只包含一条记录,为False的时候游标对象(Ifeaturecursor)为10条记录（假设Featureclass有10条记录）我经过测试提出个人的观点：1.pFeatureCursor存储的是所有符合条件的Feature对象的引用，2.Recycling的意思是回收，参数Recycling为True的时当执行这个方法IFeature pFeature=pFeatureCursor.NextFeature()上一条记录的值在内存中所占的地址就会被销毁回收，为False的时候当执行这个方法IFeature pFeature=pFeatureCursor.NextFeature()上一条记录的值依然存在在内存中。Ok，接下来以实例证明本观点：1.参数Recycling设置为True IFeatureClass pFeatureClass = (this.axMapControl1.get_Layer(0) as IFeatureLayer).FeatureClass; IFeatureCursor pFeatureCursor = pFeatureClass.Search(null, true); //IFeatureCursor pFeatureCursor = pFeatureClass.Search(null, false); List<IFeature> pFeatures = new List<IFeature>(); IFeature pFeature = pFeatureCursor.NextFeature(); while (pFeature != null) { pFeatures.Add(pFeature); pFeature = pFeatureCursor.NextFeature(); } for (int i = 0; i < pFeatures.Count; i++) { MessageBox.Show(((pFeatures.Shape as IPolygon) as IArea).Area.ToString()); }分析：pFeatures集合存储了指向FeatureClass上所有Feature的引用，但是由于Recycling参数设置为TRUE也就是说每执行一个NextFeautre方法上一条记录的Feature值在内存中被回收，所以到最后遍历pFeatures集合的时候所有的IFeature引用指向的Feature对象都为Null。所以会引发一下错误（如下图所示）：错误.jpg
2.参数Recycling设置为False IFeatureClass pFeatureClass = (this.axMapControl1.get_Layer(0) as IFeatureLayer).FeatureClass; //IFeatureCursor pFeatureCursor = pFeatureClass.Search(null, true); IFeatureCursor pFeatureCursor = pFeatureClass.Search(null, false); List<IFeature> pFeatures = new List<IFeature>(); IFeature pFeature = pFeatureCursor.NextFeature(); while (pFeature != null) { pFeatures.Add(pFeature); pFeature = pFeatureCursor.NextFeature(); } for (int i = 0; i < pFeatures.Count; i++) { MessageBox.Show(((pFeatures.Shape as IPolygon) as IArea).Area.ToString()); }分析：pFeatures集合存储了指向FeatureClass上所有Feature的引用，但是由于Recycling参数设置为False也就是说每执行一个NextFeautre方法上一条记录的Feature值在内存中依然存在，所以到最后遍历pFeatures集合的时候所有的IFeature引用指向的Feature对象都依然存在。所以会执行的很Happy（如下图所示）：正确.jpg
转自 fxlcoco：http://www.gisall.com/?uid-4359-action-viewspace-itemid-587
因此在性能方面，参见：http://www.cnblogs.com/wall/archive/2008/05/07/1186203.html
帮助中有如此论述，指出recycling参数的主要性：
The Recycling 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.
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 IMxDocumentSet 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 WendDebug.Print "Seconds: " & DateDiff("s", dt, Now) dt = Now Debug.Print "Recyle: True" Set fc = lyr.Search(qr, True) While Not fc.NextFeature Is Nothing WendDebug.Print "Seconds: " & DateDiff("s", dt, Now) End Sub
结果如下：
N=100000
Recyle: FalseSeconds: 3Recyle: TrueSeconds: 1
N=500000
Recyle: FalseSeconds: 12Recyle: TrueSeconds: 8
说明在只读查询中，将Recycling参数设为true可以提高函数效率。
转载于:https://www.cnblogs.com/willwayer/archive/2010/01/05/1639615.html
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