How Can I Persistently Modify App.Config Values in My Application?

App.Config Value Modification

App.Config files provide a convenient way to store configuration settings for applications. However, modifying these values within an application can be challenging.

In an example provided by the user, they attempted to update the "lang" key's value from "English" to "Russian" within their App.Config file. However, their code only made the change in memory and did not persist it.

Cause of Issue

The AppSettings.Set method only modifies the in-memory configuration settings. It does not write the changes back to the App.Config file.

Solution

To persist changes to the App.Config file, the following steps need to be taken:

1. Open the App.Config file for editing using ConfigurationManager.OpenExeConfiguration.
2. Locate the key whose value you want to modify using configuration.AppSettings.Settings[key].
3. Update the value of the key.
4. Save the changes to the App.Config file using configuration.Save.

Example

The following C# code demonstrates how to update the "lang" setting:

using System.Configuration;

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: In Visual Studio, changes made to App.Config files during debugging will be overwritten. To test the persistence, build the application and run it from the output directory.

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