GetRelativePath获取相对路径

         public static string GetRelativePath(string baseDirPath, string subFullPath)
         {
             // ForceBasePath to a path
             if (!baseDirPath.EndsWith("\\"))
                 baseDirPath += "\\";
             var baseUri = new Uri(baseDirPath);
             var fullUri = new Uri(subFullPath);
             var relativeUri = baseUri.MakeRelativeUri(fullUri);
             // Uri's use forward slashes so convert back to backward slashes
             return relativeUri.ToString().Replace("/", "\\");
         }