IRasterStretch接口的BackgroundValues 怎么用啊，我把代码贴出来了

<p><font face="Verdana">IRasterStretch接口的BackgroundValues 怎么用啊，我把代码贴出来了</font>，就是想批量的改显示属性，可是设置代替背景色有问题，大家帮我看看啊</p>
<p> </p>
<p><font face="Verdana">Function tttt()</font></p>
<p><font face="Verdana"></font> </p>
<p><font face="Verdana">Dim pMxDocument As IMxDocument<br/>Set pMxDocument = ThisDocument<br/>Dim pMap As IMap<br/>Set pMap = pMxDocument.FocusMap<br/>Dim LayerCount As Long<br/>LayerCount = pMap.LayerCount<br/>Dim pRLayer As IRasterLayer<br/>Dim pRaster As IRaster</font></p>
<p><font face="Verdana"> </font></p>
<p><font face="Verdana">Dim pRasterStretch As IRasterStretch<br/>Set pRasterStretch = New RasterRGBRenderer<br/> </font></p>
<p><font face="Verdana"></font> </p>
<p><font face="Verdana">Dim pRasterRGBRenderer2 As IRasterRGBRenderer2<br/>Dim pRasterRenderer As IRasterRenderer</font></p>
<p><font face="Verdana">Set pRasterRGBRenderer2 = New RasterRGBRenderer<br/>Set pRasterRenderer = pRasterRGBRenderer2</font></p>
<p><font face="Verdana">Dim pColor As IRgbColor</font></p><font face="Verdana">
<p><br/>Dim val As Double</p>
<p> <br/> Dim instance As RasterRGBRenderer<br/> <br/> </p>
<p><br/>For i = 0 To LayerCount - 1<br/>    Set pRLayer = pMap.Layer(i)<br/>    Set pRaster = pRLayer.Raster<br/>         <br/>    Set pRasterRenderer.Raster = pRaster<br/>    <br/>    <br/>    <br/>     <br/>    Set pRasterStretch = pRasterRenderer<br/>    pRasterStretch.StretchType = esriRasterStretch_NONE<br/>    pRasterStretch.Background = True<br/>   <br/>   <br/>  <br/>    <br/>    <br/>    Set pColor = New RgbColor<br/> <br/>    pColor.NullColor = True<br/>    <br/>    <br/>     <br/>    Set pRasterStretch.BackgroundColor = pColor<br/>    </p>
<p>    pRasterStretch.BackgroundValues = 1<br/>    <br/>    <br/>    pRasterRenderer.Update<br/>    <br/>    Set pRLayer.Renderer = pRasterRenderer<br/>    <br/>    Set pRasterRenderer = pRLayer.Renderer<br/>    val = pRasterStretch.BackgroundValues</p>
<p>Next i</p>
<p><br/>Dim pActiveView As IActiveView<br/>Set pActiveView = pMxDocument.ActivatedView<br/>pActiveView.Activate 0</p>
<p> </p>
<p>End Function<br/></font></p>