怎么读取ZIP包里的二级或更深层文件夹中的资源

WebClient wc = new WebClient();
            wc.OpenReadCompleted += new OpenReadCompletedEventHandler(wc_OpenReadCompleted);
            wc.DownloadProgressChanged += new DownloadProgressChangedEventHandler(wc_DownloadProgressChanged);
            wc.DownloadStringCompleted += new DownloadStringCompletedEventHandler(wc_DownloadStringCompleted);
            wc.OpenReadAsync(new Uri(@"demo.zip", UriKind.Relative), "demo.jpg");


void wc_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
        {
            String sURI = (e.UserState as String);
            StreamResourceInfo sri = new StreamResourceInfo(e.Result, null);
            StreamResourceInfo imageStream = Application.GetResourceStream(sri, new Uri(sURI, UriKind.Relative));
            BitmapImage imgsrc = new BitmapImage();
            imgsrc.SetSource(imageStream.Stream);
            T_Image.Source = imgsrc;
        }