How to Permanently Change App.Config Values in C#?

App.Config Configuration Value Modification

When attempting to modify the value of an App.Config parameter using the following code:

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

one may encounter an issue where the modification is not persisted in the App.Config file. To rectify this, it is crucial to avoid the sole use of AppSettings.Set. While AppSettings.Set modifies the value in memory, it does not persist these changes in the configuration file.

To implement a persistent change, one must utilize the following code:

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");
    }
}

This code snippet includes the following key steps:

1. Opening the App.Config file for editing using ConfigurationManager.OpenExeConfiguration.
2. Identifying the specific key to be modified using configuration.AppSettings.Settings[key].
3. Modifying the value of the identified key to the desired value.
4. Saving the changes to the App.Config file using configuration.Save().
5. Refreshing the appSettings section to ensure the changes are implemented.

When debugging the application, it is important to launch the executable from the output directory rather than the debugger to prevent the App.Config file from being overwritten during each build. The modification can be verified by opening the YourApplicationName.exe.config file in Notepad located in the output directory.

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