如何返回输出参数 [英] How to return an output parameter

问题描述

我正在尝试从此方法返回输出参数但有问题。



我尝试过：

I'm trying to return an output parameter from this method but having issue.

What I have tried:

public void GetStaffName(string id, out string Name)
    {
        try
        {
           // dt = new DataTable();
            if (con.State != ConnectionState.Open)
            {
                con.Open();
            }
            string query = "select * from stafflist where staffidno = @staffidno";
            SqlCommand sqlCmd = new SqlCommand(query, con);
            sqlCmd.Parameters.AddWithValue("@staffidno", id);
            SqlDataReader dr = sqlCmd.ExecuteReader();
            

            while (dr.Read())
            {
                string Name = dr["emp_name"].ToString();
               // return Name;
            }
             

        }
        catch (Exception ex)
        {
            throw ex;
        }
        finally
        {
            con.Close();
        }

    }

推荐答案

这几乎是你需要做的 - 除了你需要在每个代码路径上为它分配一个值，因为它是一个输出参数，并且可能是循环甚至不会执行一次。并且声明一个同名的变量是行不通的！

所以试试：

That's pretty much what you need to do - except that you need to assign a value to it on every code path because it is an output parameter and it's possible that the while loop won't execute even once. and declaring a variable of the same name won't work!
So try:

public void GetStaffName(string id, out string Name)
    {
    Name = "";
    try
        {
        if (con.State != ConnectionState.Open)
            {
            con.Open();
            }
        string query = "select * from stafflist where staffidno = @staffidno";
        using (SqlCommand sqlCmd = new SqlCommand(query, con))
            {
            sqlCmd.Parameters.AddWithValue("@staffidno", id);
            SqlDataReader dr = sqlCmd.ExecuteReader();
            if (dr.Read())
                {
                Name = dr["emp_name"].ToString();
                }
            }
        }
    catch (Exception ex)
        {
        throw ex;
        }
    finally
        {
        con.Close();
        }
    }

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