IFeatureClass.Search(IQuery Filter,bool Recycling)中的Recycling

     IFeatureClass的Search方法在AE开发中经常用到，但是对Search方法的其中一个参数bool Recycling一直不是很理解，用的时候也很随意，感觉true与false没啥区别。
ArcObjects API Reference for .NET帮助文档上这么解释:

The recycling parameter controls row 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. Features returned by a recycling cursor should not be modified. Non-recycling cursors return a separate feature object on each fetch. The features 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. In other words, if the feature retrieved by a search cursor has already been instantiated and is being referenced by the calling application, then a reference to the existing feature object is returned.

Non-recycling feature cursors returned from the Search method *MUST* be used when copying features from the cursor into an insert cursor of another class.  This is because a recycling cursor reuses the same geometry and under some circumstances all of the features inserted into the insert cursor may have the same geometry.  Using a non-recycling cursor ensures that each geometry is unique.

上面这段话大至意思为在查询时能使用true优化，其它情况最好使用false。在复制要素类时使用true会丢失图形。

下面是实际测试：将面图层的图斑融合为一个组合图斑

准备了一个面图层：

代码：

private void FeatureCursorTest(IFeatureClass featureClass)
{
    using (ComReleaser comReleaser = new ComReleaser())
    {
        object missing = Type.Missing;
        //IFeatureCursor cursor = featureClass.Search(null, true);
        IFeatureCursor cursor = featureClass.Search(null, false);
        comReleaser.ManageLifetime(cursor);
        IFeature feature = null;
        IGeometryCollection geometries = new GeometryBagClass();
        ITopologicalOperator unionedGeometry = new PolygonClass();
        while ((feature = cursor.NextFeature()) != null)
        {
            geometries.AddGeometry(feature.Shape, ref missing, ref missing);
        }
        unionedGeometry.ConstructUnion(geometries as IEnumGeometry);
        IFeature unionedFeature = featureClass.CreateFeature();
        unionedFeature.Shape = unionedGeometry as IGeometry;
        unionedFeature.Store();
    }
}

结果：

确实，在Recycling为true时只保留了最后一个几何图形。就像网上很多大神说的传值和传址吧。即参数Recycling为True的时候理解为传引用，为False的时候理解为传值。在使用true时，如果feature已存在则会使用该对象，而false确保每次返回唯一图形。