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("/", "\\");
        }