public async Task <List <Currency> > GetCurrencyAsync()
        {
            List <Currency> currencyList = new List <Currency>();

            using (var client = new HttpClient()){
                var response = await client.GetAsync(tcmbUrl);

                using (HttpContent content = response.Content){
                    var result = await content.ReadAsStreamAsync();

                    CustomXmlSerializer <Currency> serializer = new CustomXmlSerializer <Currency>();
                    currencyList = serializer.Build("Tarih_Date").GetList(result);
                }
            }
            currencyList.ForEach(p => {
                p.CurrencyDate = date;
            });
            return(currencyList);
        }