App.Config Value Modification Quandary

In the provided code snippet, an attempt is made to modify a value in the App.Config file. However, this modification is not persisting as expected. To identify the source of this problem, let's delve into the provided code and explore potential issues.

The code segment:

lang = "Russian";
private void Main_FormClosing(object sender, FormClosingEventArgs e)
{
     System.Configuration.ConfigurationManager.AppSettings.Set("lang", lang);
}

indeed modifies the value of the "lang" key in the App.Config file. However, as highlighted in the response, this modification occurs solely in memory and is not persisted to the physical configuration file.

The key to resolving this issue lies in recognizing that ConfigurationManager.AppSettings.Set("lang", lang) only makes temporary, in-memory changes. To persist these changes to the App.Config file, additional steps are necessary.

The response introduces a revised code snippet specifically tailored for a console application:

class Program
{
    static void Main(string[] args)
    {
        UpdateSetting("lang", "Russian");
    }

    private static void UpdateSetting(string key, string value)
    {
        Configuration configuration = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
        configuration.AppSettings.Settings[key].Value = value;
        configuration.Save();

        ConfigurationManager.RefreshSection("appSettings");
    }
}

Within this code:

1. ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None) is used to open the App.Config file in a writable state.
2. The desired key-value pair is then modified using configuration.AppSettings.Settings[key].Value = value.
3. Most importantly, the configuration.Save() method is invoked to persist these changes to the App.Config file.
4. Finally, ConfigurationManager.RefreshSection("appSettings") is utilized to refresh the loaded App.Config section, ensuring that any subsequent retrieval operations read the updated values.

By leveraging this updated code, the value modifications made to the App.Config file are now successfully persisted, resolving the issue and allowing for the desired language setting change.