字符串中的值不正确

我有一个字符串值的问题。该字符串是全局声明的。字符串为name_file_image

我有这样的代码:

            // iterate image files
            foreach (XElement node in xml.Element("graphics").Elements("file"))
            {
                // pick image 
                if (node.Attribute("type").Value == "image")
                {
                    // demoing that we found something                
                    //MessageBox.Show(node.Element("fileurl").Value);
                    string url_image = node.Element("fileurl").Value;
                    string[] array = url_image.Split('/');
                    **name_file_image** = array[array.Length - 1];
                    //MessageBox.Show(**name_file_image**);
                    WebClient webClient = new WebClient();
                    webClient.OpenReadCompleted += new OpenReadCompletedEventHandler(webClient_image);
                    webClient.OpenReadAsync(new Uri(url_image));
                }
            } 
    void webClient_image(object sender, OpenReadCompletedEventArgs e)
    {
        try
        {
            if (e.Result != null)
            {
                // Save image to Isolated Storage

                // Create virtual store and file stream. Check for duplicate JPEG files.
                using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile.GetUserStoreForApplication())
                {
                    if (myIsolatedStorage.FileExists(**name_file_image**))
                    {
                        myIsolatedStorage.DeleteFile(**name_file_image**);
                    }
                    IsolatedStorageFileStream fileStream = new IsolatedStorageFileStream(name_file_image, FileMode.Create, myIsolatedStorage);

                    BitmapImage bitmap = new BitmapImage();
                    bitmap.SetSource(e.Result);
                    WriteableBitmap wb = new WriteableBitmap(bitmap);
                    wb.SaveJpeg(fileStream, wb.PixelWidth, wb.PixelHeight, 0, 85);
                    fileStream.Close();
                    //MessageBox.Show(name_file_image);
                }
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    } 

我从内存中的文件中读取XML，我想用XML中的名称保存图像。但我有个问题。变量字符串总是具有相同的名称。我想代码是不正确的。任何帮助吗?