private string BuildRequest(string orderNo, string productName, int totalFee, string customerIP, EnumWePayTradeType tradeType)
{
SortedDictionary <string, string> dicParam = CreateParam(orderNo, productName, totalFee, customerIP, tradeType);
string signString = CreateURLParamString(dicParam);
string key = tradeType == EnumWePayTradeType.APP ? WepayConfig.WEPAY_APP_KEY : WepayConfig.WEPAY_WEB_KEY;
string preString = signString + "&key=" + key;
string sign = MD5Helper.Sign(preString, WepayConfig.WEPAY_CHARTSET).ToUpper();
dicParam.Add("sign", sign);
return(BuildForm(dicParam));
}