如何从C#中的应用程序配置获取连接字符串 [英] how to get connection string from app config in c#

问题描述

我的app.config文件:

My app.config file:

<configuration>
    <connectionStrings>
        <add name="MegaPixelBizConn"
            connectionString="Data Source=PSHERATH-PC;Initial Catalog=MegaPixelBiz;Integrated Security=True"
            providerName="System.Data.SqlClient" />
    </connectionStrings>
</configuration>

然后我创建了DBConnection文件:

Then I created DBConnection file:

class DBConnection
    {
        #region Database connection method
        public SqlConnection Connect()
        {
            SqlConnection conn = new SqlConnection();
            conn.ConnectionString = ConfigurationManager.ConnectionStrings["MegaPixelBizConn"].ToString();

            try
            {
                conn.Open();
            }
            catch
            {
            }
            return conn;
        }
        #endregion
    }

这是我的登录表格:

SqlCommand cmd;
        DataSet ds = new DataSet();
        DBConnection db = new DBConnection();

        private void btnLogin_Click(object sender, EventArgs e)
        {
            try
            {
                if (txtUserName.Text == "" || txtPassword.Text == "")
                {
                    lblError.Visible = true;
                    lblError.Text = "*Enter UserName and Password";
                    //MessageBox.Show(" Enter UserName and Password .");
                    return;
                }
                else
                {
                    string sql = "SELECT * FROM login_info WHERE userName = '" + txtUserName.Text + "' and password = '" + txtPassword.Text + "'";
                    cmd = new SqlCommand(sql, db.Connect());
                    SqlDataAdapter da = new SqlDataAdapter(cmd);
                    da.Fill(ds);
                    int i = ds.Tables[0].Rows.Count;
                    if (i == 1)
                    {
                        this.Hide();
                        Home hm = new Home();
                        hm.Show();
                        ds.Clear();

                    }
                    else
                    {
                        lblError.Text = "*Not Registered User or Invalid Name/Password";
                        //MessageBox.Show("Not Registered User or Invalid Name/Password");
                        txtPassword.Text = "";
                    }
                }


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


        }

但是当我的项目运行时，会出现以下错误:你调用的对象是空的."请给我一个解决方案.我使用所有合适的参考书

But when my project run, this error come: "Object reference not set to an instance of an object." please give me a solution. I use all suitable references

推荐答案

尝试

SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["ConnectionStringNameFromWebConfig"].ConnectionString);

应该可以

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