private async void LoadListingInformationAsync()
        {
            try
            {
                // Query the Windows Phone Store for the in-app products defined for the currently-running app.
                var listingInformation = await CurrentApp.LoadListingInformationAsync();
                foreach (var v in listingInformation.ProductListings)
                {
                    Products.Add(new ProductViewModel() { Title = v.Value.Name, ProductId = v.Value.ProductId, ImageUri = v.Value.ImageUri });
                }
            }
            catch
            {
                // An exception is expected to be raised by CurrentApp.LoadListingInformationAsync() 
                //when it is not called from an app installed from the Windows Phone Store.
            }
        }

private async void PurchaseProduct(string productId)
{
    try
    {
        // Kick off purchase; don‘t ask for a receipt when it returns
        await CurrentApp.RequestProductPurchaseAsync(productId, false);

        // Now that purchase is done, give the user the goods they paid for
        // (DoFulfillment is defined later)
        //DoFulfillment();
    }
    catch (Exception ex)
    {
        // When the user does not complete the purchase (e.g. cancels or navigates back from the Purchase Page), 
        // an exception with an HRESULT of E_FAIL is expected.
    }
}

public void DoFulfillment()
{
    var productLicenses = CurrentApp.LicenseInformation.ProductLicenses;
    DistributeProduct(productLicenses);
}

private void DistributeProduct(IReadOnlyDictionary<string, ProductLicense> productLicenses)
{
    var bagOfSilver = new Regex(@"Bag\.Silver\.(\d+)");
    foreach (ProductLicense license in productLicenses.Values)
    {
        if (license.IsConsumable && license.IsActive)
        {
            var m = bagOfSilver.Matches(license.ProductId);
            if ((m.Count == 2) && (m[1].Success))
            {
                m_silverCount += int.Parse(m[1].Value);
                CurrentApp.ReportProductFulfillment(license.ProductId);
            }
        }
    }
}

public async Task<bool> LoadLevelAsync(string levelProductId)
{
    var license = CurrentApp.LicenseInformation.ProductLicenses[levelProductId];
    if (!license.IsActive)
    {
        // User doesn‘t own this level
        return false;
    }
    if (!IsLevelDownloaded(levelProductId))
    {
        var receiptXml = await CurrentApp.GetProductReceiptAsync(levelProductId);
        await DownloadLevelAsync(receiptXml);
    }
    // TODO: Load the level
    return true;
}

private async Task DownloadLevelAsync(string receiptXml)
{
    var webReq = (HttpWebRequest)WebRequest.Create(sc_DownloadUrl);
    webReq.Method = "POST";
    AddStringToWebRequestStream(webReq, receiptXml);
    WebResponse response = await webReq.GetResponseAsync();
    // TODO: Save the level to disk
}