[求助]怎样用ienvelop接口？

给定一个文件（shp、dwg或者其他）路径，怎样用ienvelope接口获得边界信息？<br>
是不是要先建个workspace？小弟不才，还请指教！能不能帮忙写段程序啊！

我是这么写的<br>
<br>
IWorkspaceFactory outputWorkspaceFactory = new ESRI.ArcGIS.DataSourcesFile.ShapefileWorkspaceFactoryClass();<br>
            IFeatureWorkspace outputFeatureWorkspace =
outputWorkspaceFactory.OpenFromFile(System.IO.Path.GetDirectoryName(textBox2.Text),
0) as IFeatureWorkspace;<br>
            IFeatureClass outputFeatureClass =
outputFeatureWorkspace.OpenFeatureClass(System.IO.Path.GetFileNameWithoutExtension(textBox2.Text));<br>
            IEnvelope env = new EnvelopeClass();<br>
            xmax = env.XMax;<br>
<br>
到最后一步的报错：The operation was attempted on an empty geometry.

搞定了，就是最后没有给env赋值！见笑了！