var pfn = Package.Current.Id.FamilyName;

await Launcher.LaunchUriAsync(new Uri("ms-windows-store://review/?PFN=" + pfn));

public async Task<bool> ShowRatingReviewDialog()

{

    StoreSendRequestResult result = await StoreRequestHelper.SendRequestAsync(

        StoreContext.GetDefault(), , String.Empty);

    if (result.ExtendedError == null)

    {

        JObject jsonObject = JObject.Parse(result.Response);

        if (jsonObject.SelectToken("status").ToString() == "success")

        {

            // The customer rated or reviewed the app.

            return true;

        }

    }

    // There was an error with the request, or the customer chose not to

    // rate or review the app.

    return false;

}