Why Doesn't Changing App.Config Values with ConfigurationManager.AppSettings.Set Persist the Changes?

App.Config Value Cannot Be Changed

The App.Config file is an XML file that stores configuration settings for a .NET application. These settings can be accessed at runtime using the ConfigurationManager class.

One common issue is that changes made to the AppSettings section using ConfigurationManager.AppSettings.Set do not persist to the actual App.Config file. This is because AppSettings.Set only changes the values in memory and does not save them to the file.

To persist the changes, one must explicitly save them using Configuration.Save(). Here's an example in C#:

using System.Configuration;

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

This code not only changes the value in memory but also saves it to the App.Config file.

Additional Notes:

• Ensure that the executable is not run from within the Visual Studio debugger, as this can overwrite the App.Config file.
• The updated App.Config file can be found in the application's output directory with the name YourApplicationName.exe.config.

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