连接字符串属性尚未初始化 C# 和 XML

Question

我正在尝试测试连接并将凭据保存在配置文件中，但我不断收到此错误“尚未初始化 ConnectionString 属性”

这是 C# 代码

private void button1_Click(object sender, EventArgs e)
    {
        try
        {
            StringBuilder str = new StringBuilder("server=");
            str.Append(textBox1.Text);
            str.Append(";database=");
            str.Append(textBox2.Text);
            str.Append(";UID=");
            str.Append(textBox3.Text);
            str.Append(";password=");
            str.Append(textBox4.Text);
            string strcon = str.ToString();
            updateConfigFile(strcon);

            SqlConnection con = new SqlConnection();

            //Refresh Connection String each time else
            //it will use previous connection string.
            ConfigurationManager.RefreshSection("connectionStrings");
            con.ConnectionString = ConfigurationManager.ConnectionStrings["con"].ConnectionString;

            //Check the new connection string is working or not
            con.Open();
            SqlCommand cmd = new SqlCommand("select * from egtab3");
            cmd.ExecuteNonQuery();
            MessageBox.Show("Connected Sucessfully");
            con.Close();

        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }

    public void updateConfigFile(string con)
    {
        //Updating Config File
        XmlDocument xmldoc = new XmlDocument();

        //Loading the Config File
        xmldoc.Load(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
        foreach (XmlElement xElement in xmldoc.DocumentElement)
        {
            if (xElement.Name == "connectionStrings")
            {
                //Setting the connection string
                xElement.FirstChild.Attributes[4].Value = con;
            }
        }
        //writing the connection string in config file
        xmldoc.Save(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
    }

这是xml代码

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<connectionStrings>
<add name="con" providerName="using System.Data.SqlClient" 
connectionString=""/>
</connectionStrings>
</configuration>

Answer 1

在从配置获取之前添加更新

private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                StringBuilder str = new StringBuilder("server=");
                str.Append(textBox1.Text);
                str.Append(";database=");
                str.Append(textBox2.Text);
                str.Append(";UID=");
                str.Append(textBox3.Text);
                str.Append(";password=");
                str.Append(textBox4.Text);

                updateConfigFile(str);

                SqlConnection con = new SqlConnection();

                //Refresh Connection String each time else
                //it will use previous connection string.
                ConfigurationManager.RefreshSection("connectionStrings");
                con.ConnectionString = ConfigurationManager.ConnectionStrings["con"].ConnectionString;

                //Check the new connection string is working or not
                con.Open();
                SqlCommand cmd = new SqlCommand("select * from egtab3");
                cmd.ExecuteNonQuery();
                MessageBox.Show("Connected Sucessfully");
                con.Close();

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }