How Can I Persistently Change App.Config Values in C#?

Changing App.Config Values

Problem:

An attempt to modify a key-value pair in the App.Config using System.Configuration.ConfigurationManager.AppSettings.Set does not persist the change to the configuration file.

Code:

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

Reason:

AppSettings.Set only modifies the configuration settings in memory; it does not update the actual configuration file.

Solution:

To persist the changes, use the UpdateSetting function:

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");
    }
}

Note:

• When debugging, build the project and launch the executable from the output directory, as Visual Studio overwrites the App.Config file during debugging.
• To verify the changes, open the YourApplicationName.exe.config file in the output directory.

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