Question

我决定在SQL中保存所有设置。如果我想读取前。来自SQL DB的comport，而不是我收到错误： “c＃名称”comportnumber“在当前上下文中不存在” 我应该改变什么来解决它？

    SqlCeConnection conn = new SqlCeConnection("Data Source = \\Program Files\\myprogram\\db.sdf; Password ='mypassword'");
        conn.Open();
            SqlCeCommand cmd = new SqlCeCommand("SELECT * FROM [COMPORT]", conn);
            SqlCeDataReader rdr = cmd.ExecuteReader();
            cmd.Connection = conn;
            cmd.ExecuteNonQuery();
            while (rdr.Read())
            {
                string comportnumber = rdr.GetString(0);
            }
        serialPort1.PortName = comportnumber;
        conn.Close();
        serialPort1.Close();
        if (!serialPort1.IsOpen)
            serialPort1.Open();

Answer 1

您的问题的问题是您的comportnumber变量的范围仅限于while循环中相对较小的括号部分。只需移动声明即可。但是你也有其他问题 - 请注意我是如何重组代码的。

string comportnumber = "";
using (SqlCeConnection conn = new SqlCeConnection("Data Source = \\Program Files\\myprogram\\db.sdf; Password ='mypassword'"))
using (SqlCeCommand cmd = new SqlCeCommand("SELECT * FROM [COMPORT]", conn))
{
    conn.Open();
    using (SqlCeDataReader rdr = cmd.ExecuteReader())
    {    
        while (rdr.Read())
        {
            comportnumber = rdr.GetString(0);
        }
    }
}
serialPort1.PortName = comportnumber;
serialPort1.Close();

if (!serialPort1.IsOpen)
    serialPort1.Open();

Answer 2

如你所知，comportnumber只存在于while循环的范围内。尝试将其更改为：

string comportnumber = string.Empty;
while (rdr.Read())
{
    comportnumber = rdr.GetString(0);
}
serialPort1.PortName = comportnumber;

当前上下文中不存在名称“comportnumber”

2 个答案: