[求助]OpenDialog打开ESRI GRID文件(c#+ae)问题

我想利用OpenDialog打开ESRI GRID文件，却实现不了？请教大虾帮助。c#+ae代码如下：

OpenFileDialog filedlg_addraster = new OpenFileDialog();
filedlg_addraster.Filter = "ESRI GRID||All Files|*.*";
if (filedlg_addraster.ShowDialog() == DialogResult.OK)
           {
               string m_FileName = Path.GetFileName(filedlg_addraster.FileName);
               string m_FilePath = Path.GetDirectoryName(filedlg_addraster.FileName);
               IWorkspaceFactory iWsFactory = new RasterWorkspaceFactoryClass();
               IRasterWorkspace iRasWs;
               if(iWsFactory.IsWorkspace(m_FilePath))
               {
                   iRasWs = (IRasterWorkspace)iWsFactory.OpenFromFile(m_FilePath, 0);
                   IRasterDataset iRasDs = iRasWs.OpenRasterDataset(m_FileName);                
                   IRasterLayer iRLayer = new RasterLayerClass();                    
                   iRLayer.CreateFromDataset(iRasDs);
                   ILayer iLayer = iRLayer;
                   axMapControl1.AddLayer(iLayer, 0);
               }