[求助]IRawPixels.Write方法

<H2>IRawPixels.Write方法</H2>
<DIV>IRawPixels.Write Method<BR>If transactioning is enabled, this write is persisted temporarily to a memory cache that allows undo support; otherwise, the data is persisted directly to disk at this time.<BR>If transactioning is enabled,是什么意思？怎么就能让它enable，我想调用这个方法后，结果在内存里暂时存在，但是我现在write完之后，都是永久保存，怎么样可以暂时保存？谢谢。</DIV>

<P> IPoint op=new PointClass();<BR>      op.X=100;<BR>      op.Y=20;<BR>      ISpatialReferenceFactory isrf=new SpatialReferenceEnvironmentClass();<BR>      ISpatialReference isr=isrf.CreateGeographicCoordinateSystem((int)esriSRGeoCSType.esriSRGeoCS_WGS1984);<BR>      IWorkspaceFactory iwf = new RasterWorkspaceFactoryClass();<BR>      IRasterWorkspace2 irws = (IRasterWorkspace2)iwf.OpenFromFile("c:\\temp", 0);<BR>      IRasterDataset irds = irws.CreateRasterDataset("test", "GRID", op, 252, 202, 0.0995, 0.0995, 1, rstPixelType.PT_FLOAT, isr, true);<BR>      IRaster ir = irds.CreateDefaultRaster();<BR>      IRasterBandCollection rbc = (IRasterBandCollection)ir;<BR>      IRawPixels irpixels = (IRawPixels)rbc.Item(0);<BR>      IRasterProps irProps = (IRasterProps)irpixels;<BR>      IPnt rasterOP = new PntClass();<BR>      rasterOP.SetCoords(0, 0);<BR>      IPnt rasterSize = new PntClass();<BR>      rasterSize.SetCoords(irProps.Width, irProps.Height);<BR>      IPixelBlock3 pixBlock =(IPixelBlock3) irpixels.CreatePixelBlock(rasterSize);</P>
<P>      pixBlock.set_PixelData(0, (System.Object)dat[0]);<BR>      System.Object cachePointer = irpixels.AcquireCache();<BR>      irpixels.Write(rasterOP, (IPixelBlock)pixBlock);<BR>      irpixels.ReturnCache(cachePointer);<BR>     <BR>      cachePointer = null;</P>
<P>      irProps = null;<BR>      irpixels = null;<BR>      rbc = null;<BR>      ir = null;<BR>      irds = null;<BR>      GC.Collect();</P>
<P>      IRasterLayer m_raster = new RasterLayerClass();<BR>      m_raster.CreateFromFilePath("c:\\temp\\test");<BR>      axMapControl1.AddLayer(m_raster);   <BR>      If transactioning is enabled是启用事务机制  System.Object cachePointer = irpixels.AcquireCache();<BR>      irpixels.Write(rasterOP, (IPixelBlock)pixBlock);<BR>      irpixels.ReturnCache(cachePointer);</P>
<P>System.Object cachePointer = irpixels.AcquireCache();是开始，irpixels.ReturnCache(cachePointer);是结束。不要这2句直接write的话，就直接保存。</P>
<P>不过在我这里我发现有点问题，就是不管是直接write还是用事务机制，如果不解除除对新建Raster的的各个AO对象的引用（就是代码中的cachePointer = null;.....;GC.Collect();，当然等到程序结束也是可以的，那时候对所有AO对象的引用自然就解除了) ，对Pixel值的更改是不会被保存的，就好像用缓存写了文件最后忘记Flush了一样，不知道是不是Bug。我用的win2003+ArcGIS desktop 9.2+ArcEngine 9.2.</P>
<P>我猜LZ的意思是想在内存中建立一个临时的Raster，那应该在CreateRasterDataset("test", "GRID", op, 252, 202, 0.0995, 0.0995, 1, rstPixelType.PT_FLOAT, isr, true)时把"GRID"换成"MEM"就可以了。<BR><BR>     </P>