求要素类中一部分要素的并集

AE中有时候要根据指定的条件求要素类中的要素的并集。生成游标，取每条要素，然后求并，最后释放游标的过程很麻烦。

<pre name="code" class="csharp">用IEnumGeometryBind 接口，可以简化工作。

private IGeometry GetFrameGeometry(IFeatureClass frameClass, IQueryFilter filter)
{

<span style="white-space:pre">	</span>    // <span style="font-family: Arial, Helvetica, sans-serif;">EnumFeatureGeometryClass </span><span style="font-family: Arial, Helvetica, sans-serif;"> 在ESRI.ArcGIS.Geodatabase</span><span style="font-family: Arial, Helvetica, sans-serif;">	</span>命名空间下
IEnumGeometry enumGeometry = new EnumFeatureGeometryClass();
try
{
filter.SubFields = frameClass.ShapeFieldName;
IEnumGeometryBind bind = enumGeometry as IEnumGeometryBind;
bind.BindGeometrySource(filter, frameClass);

enumGeometry.Reset();
IGeometry firstGeometry = enumGeometry.Next();

ITopologicalOperator topo = firstGeometry as ITopologicalOperator;
topo.ConstructUnion(enumGeometry);

return topo as IGeometry;
}
catch (Exception ex)
{
LogHelper.Error.Append(ex);
return null;
}
finally
{
ComReleaser.ReleaseCOMObject(enumGeometry);
}
}