set connection string in app.config in c#

Question

Why my code doesn't work

app.config

<connectionStrings>
    <add name="string.name"
        connectionString=""
        providerName="System.Data.SqlClient" />
</connectionStrings>

in c#

private void addnewstring()
    {         
        Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
        config.AppSettings.Settings.Remove("string.name");            
        config.AppSettings.Settings.Add("string.name", "new connection string");            
        config.Save(ConfigurationSaveMode.Modified);
        ConfigurationManager.RefreshSection("connectionStrings");                       
    }

code in c# doesn't change connection string in app.config

Answer 1

You need to be modifying the ConnectionStrings - your code is just accessing the Settings. Try this :

  Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
  config.ConnectionStrings.ConnectionStrings.Remove("string.name");
  config.ConnectionStrings.ConnectionStrings.Add(new ConnectionStringSettings("string.name", "new connection string"));
  config.Save(ConfigurationSaveMode.Modified);
  ConfigurationManager.RefreshSection("connectionStrings");

Answer 2

Try this, shold be work

var config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
var connectionStringsSection = (ConnectionStringsSection)config.GetSection("connectionStrings");
connectionStringsSection.ConnectionStrings["string.name"].ConnectionString = "new connection string";
config.Save();
ConfigurationManager.RefreshSection("connectionStrings");