Question

我正在使用带有c＃的asp.net开发一个Web应用程序，使用的代码如下所示。

public string fnDisplayManualRecords1(string patid)
{
    string cmdString = "select top 1 (patientid) from Patient_Data where PatientID like '"+patid+"%' order by PatientID desc";
    con = new SqlConnection(str);

    try
    {
        con.Open();
        cmd = new SqlCommand(cmdString, con);
        cmd.Parameters.AddWithValue("@patid", patid);
        string result = cmd.ExecuteScalar().ToString();
        return result;
    }
    catch (Exception ex)
    {

        log.Debug("Error: Inside catch block of fnCreateManualRecords");
        log.Error("Error msg:" + ex);

        log.Error("Stack trace:" + ex.StackTrace);
        //transaction.Rollback();
        return ex.ToString();
    }

    finally
    {
        con.Close();
    }


}

这是一个被调用的函数，如下所示，它适用于正确的数据，但当它捕获异常并且它将在下面显示的文本框中显示异常消息 System.NullReferenceException: Object reference not set to an instance of an object. at myConnection.fnDisplayManualRecords1(String patid) in d:\Shreyas\PMS_CMR\pms_production_manual_updation\App_Code\Connection.cs:line 2157

  string result = obj.fnDisplayManualRecords1(patid);
  txtlast.Text = result.ToString();

现在我只需要将异常消息更改为“No Data Found”而不是上面显示的实际异常消息。

Answer 1

NullReferenceException 的原因是应检查 返回值为null。不要忘记关闭SqlConnection 作为SqlCommand：使用构建，恕我直言，是最佳选择。

public string fnDisplayManualRecords1(string patid) {
  string cmdString = "select top 1 (patientid) from Patient_Data where PatientID like '"+patid+"%' order by PatientID desc";

  using (new SqlConnection(str)) {
    try {
      con.Open();

      using (cmd = new SqlCommand(cmdString, con)) {
        cmd.Parameters.AddWithValue("@patid", patid);

        Object data = cmd.ExecuteScalar();

        // Check if returned value is null: special case  
        if (Object.ReferenceEquals(null, data))
          return "No data found"; // <- Your message here

        return data.ToString(); 
      }
    }
    catch (DataException ex) { // <- Ordinary data (SQL server) errors
      log.Debug("Error: Inside catch block of fnCreateManualRecords");
      log.Error("Error msg:" + ex);
      log.Error("Stack trace:" + ex.StackTrace);

      return ex.ToString();
    }
  }
}

Answer 2

try
{
    // Do stuff
}
catch (Exception ex) 
{
    // Log error

    // Return friendly string
    return "No Data Found";
}

Answer 3

使用自定义消息进行例外处理并将其返回。：）

try
{
    con.Open();
    cmd = new SqlCommand(cmdString, con);
    cmd.Parameters.AddWithValue("@patid", patid);
    string result = cmd.ExecuteScalar().ToString();
    return result;
}
catch (Exception ex)
{

    log.Debug("Error: Inside catch block of fnCreateManualRecords");
    log.Error("Error msg:" + ex);

    log.Error("Stack trace:" + ex.StackTrace);
    //transaction.Rollback();
     //Custom Exception
     Exception sqlException= new Exception("No Data Found");
     return sqlException;
    //return ex.ToString();
}

finally
{
    con.Close();
}

在文本框中显示的异常消息在函数中处理时应该更改为简单的错误消息。

3 个答案: