如何在活动结束时检索照片ID？

Question

  

可能重复：
  How to retrieve post ID for a post i’ve just made via the Facebook API

我正在尝试使用Facebook C＃SDK，并希望找到用于在我的应用中将照片发布到墙上时使用的变量。我知道我需要找到照片的ID，但我运气不好。我尝试使用_lastMessageID，但它没有用。这是我正在使用的代码中没有在postingPictureUrl中的必要变量：

    private async void PostToWall_Click(object sender, RoutedEventArgs e)
    {
        try
        {
            dynamic parameters = new ExpandoObject();
            parameters.message = txtMessage.Text;

            StorageFile imageFile = await Windows.Storage.StorageFile.GetFileFromApplicationUriAsync(new Uri("ms-appx:///Images/photo.png"));
            IRandomAccessStream fileStream = await imageFile.OpenAsync(FileAccessMode.Read);
            var reader = new Windows.Storage.Streams.DataReader(fileStream.GetInputStreamAt(0));
            await reader.LoadAsync((uint)fileStream.Size);
            byte[] pixels = new byte[fileStream.Size];
            reader.ReadBytes(pixels);
            parameters.picture = new FacebookMediaObject
            {
                ContentType = "image/png",
                FileName = "photo.png",

            }.SetValue(pixels);
            dynamic result = await _fb.PostTaskAsync("me/photos", parameters);
            _lastMessageId = result.id;
            txtMessage.Text = string.Empty;
            btnDeleteLastMessage.IsEnabled = true;
            string postedPictureUrl = string.Format("https://graph.facebook.com/{0}/photos?&access_token={2}", _userId, _fb.AccessToken"); //this is where I need to retrieve the id of the photo...
            myPostedPainting.Source = new BitmapImage(new Uri(postedPictureUrl));
        }
        catch (FacebookApiException ex)
        {
            // handle error message
        }
    }