/*获取指定时间区间中用户所有的交易记录*/
 public AllTransactionInfo GetTransactionHistory(string userID, string password, DateTime? startDate, DateTime? endDate) {
     UserService userService = new UserService();
     UserInfo userInfo = userService.Login(userID, password);
     if (userInfo.ErrorMessage == null) {
         return userService.GetTransactionHistory(startDate, endDate);
     }
     else {
         AllTransactionInfo allTransactionInfo = new AllTransactionInfo();
         allTransactionInfo.ErrorMessage = userInfo.ErrorMessage;
         return allTransactionInfo;
     }
 }