C# - formatting of local database connection string (.sdf file)

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C#

database

connectionstring

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hi, i am able to connect to my local db file .sdf directly with my winform app. but unable to do so when i am using an connstring. here is what i have tried

1. using app.config file

var config =  ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            var connectionStringsSection = (ConnectionStringsSection)config.GetSection("connectionStrings");
            connectionStringsSection.ConnectionStrings["DEVID"].ConnectionString = textBox6.Text;
            config.Save();
            ConfigurationManager.RefreshSection("connectionStrings");
            SqlCeConnection con = new SqlCeConnection();
            string DEVID = ConfigurationManager.ConnectionStrings["DEVID"].ConnectionString;
            con.ConnectionString = DEVID; // getting error as "object reference not set"
//SqlCeConnection con = new SqlCeConnection(DEVID); // in my app.config file i set my connection string = "Data Source=C:\Users\john\Documents\Visual Studio 2010\Projects\AECCS\AECCS\Database1.sdf

2. using direct string variable

//SqlCeConnection con = new SqlCeConnection(@"Data Source=C:\Users\john\Documents\Visual Studio 2010\Projects\AECCS\AECCS\Database1.sdf"); // this is the actual conn string value
            string connstring1 = "\"Data Source=" + textBox6.Text + "\"";
            string connstring2 = "@"+connstring1;
            textBox2.Text = connstring2; // matches exactly with my actual connection string, but still not getting to connect with .sdf file
SqlCeConnection con = new SqlCeConnection(connstring2); // getting error as format of initialization string does not conform at index 0""

please help me out to solve the issue

What I have tried:

//SqlCeConnection con = new SqlCeConnection(@"Data Source=C:\Users\john\Documents\Visual Studio 2010\Projects\AECCS\AECCS\Database1.sdf"); // this is the actual conn string value
string connstring1 = "\"Data Source=" + textBox6.Text + "\"";
string connstring2 = "@"+connstring1;
textBox2.Text = connstring2; // matches exactly with my actual connection string, but still not getting to connect with .sdf file
SqlCeConnection con = new SqlCeConnection(connstring2); // getting error as "format of initialization string does not conform at index 0"