IFeatureCursor和ICursor的转换问题

现有两个接口ICursor和IFeatureCursor，分别由类Cursor和FeatureCursor实现。其关系如图所示：<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

<?xml:namespace prefix = v ns = "urn:schemas-microsoft-com:vml" /><shapetype id="_x0000_t75" stroked="f" filled="f" path="m@4@5l@4@11@9@11@9@5xe" o:preferrelative="t" o:spt="75" coordsize="21600,21600"><stroke joinstyle="miter"></stroke><formulas><f eqn="if lineDrawn pixelLineWidth 0"></f><f eqn="sum @0 1 0"></f><f eqn="sum 0 0 @1"></f><f eqn="prod @2 1 2"></f><f eqn="prod @3 21600 pixelWidth"></f><f eqn="prod @3 21600 pixelHeight"></f><f eqn="sum @0 0 1"></f><f eqn="prod @6 1 2"></f><f eqn="prod @7 21600 pixelWidth"></f><f eqn="sum @8 21600 0"></f><f eqn="prod @7 21600 pixelHeight"></f><f eqn="sum @10 21600 0"></f></formulas><path o:connecttype="rect" gradientshapeok="t" o:extrusionok="f"></path><lock aspectratio="t" v:ext="edit"></lock></shapetype><shape id="_x0000_i1025" style="WIDTH: 174.75pt; HEIGHT: 369.75pt" type="#_x0000_t75"><imagedata o:title="Cursor和FeatureCursor" src="file:///C:/DOCUME~1/ADMINI~1/LOCALS~1/Temp/msohtml1/01/clip_image001.png"></imagedata></shape>

现有如下用法：

try

{

pQueryFilter.SubFields = "";

pQueryFilter.WhereClause = "FID = " + this.dataGridView1.Rows[e.RowIndex].Cells[0].Value.ToString();

//从SelectionSet中选出来,不要从从这个图层中选择,这样可以减少搜索时间

pSelectionSet.Search(pQueryFilter, false, out pCursor);

//下面这个转换莫名其妙，因为IFeatureCursor继承于ICursor

pFeatureCursor = pCursor as IFeatureCursor;

pFeature = pFeatureCursor.NextFeature();

if (pFeature != null)

{

pGeometry = pFeature.Shape;

this.axMapControl1.FlashShape(pGeometry, 3, 200, obj);

}

}

catch

{

}

习惯上认为IFeatureCursor可以通过QI转换为ICursor，但是这里为什么可以反过来进行呢？这个地方想的一直不是很明白，希望了解的朋友能不吝赐教。