Change in application configuration without application restart

Question

I have following issue: I'm introducing new feature into application (run as Windows Service) and I would like to have that new feature controlled (on/off) using some kind of configuration file entry (myKey). I can store config entry in app.config but if I want to change it from on->off or otherwise it would require to restart Windows Service, and I want to avoid it. I want my application to run and pick up changes in configuration.

The question is: is there a build in mechanism in .NET that addresses that problem ? I guess I could create my own config file, then use FileSystemWatcher etc... But perhaps .NET allows to use external config files and will reload value ??

ConfigurationManager.AppSettings["myKey"]

Thanks, Pawel

EDIT 1: Thanks for replies. However I wrote following snippet and it doesn't work (I tried creating appSettingSection in both places: before and inside loop):

static void Main(string[] args)
{
    Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
    // AppSettingsSection appSettingSection = (AppSettingsSection)config.GetSection("appSettings");
    for (int i = 0; i < 10; i++)
    {
        ConfigurationManager.RefreshSection("appSettings");
        AppSettingsSection appSettingSection = (AppSettingsSection)config.GetSection("appSettings");
        string myConfigData = appSettingSection.Settings["myConfigData"].Value; // still the same value, doesn't get updated
        Console.WriteLine();
        Console.WriteLine("Using GetSection(string).");
        Console.WriteLine("AppSettings section:");
        Console.WriteLine(
          appSettingSection.SectionInformation.GetRawXml()); // also XML is still the same
        Console.ReadLine();
    }
}

I manually edit config file when application stops on Console.ReadLine().

Sensillum

Answer 1

Once the original app.config file is loaded, it's values are cached so as you know, you'll have to restart the app. The way around this is to create a new config object and read the keys manually like this:

var appConfig = ConfigurationManager.OpenExeConfiguration(Assembly.GetExecutingAssembly().Location);
string myConfigData = appConfig.AppSettings.Settings["myConfigData"].Value;

Michaelamichaele

Thanks! But still: that way every time when I access myConfigData I would have to create new config object in order to be sure that appConfig.AppSettings.Settings["myConfigData"].Value is consistent with underlying value in app.config file? – Sensillum

Just call ConfigurationManager.RefreshSection("appSettings"); before you call appConfig.AppSettings.Settings["myConfigData"].Value; which will force the application to read the new & changed settings. Otherwise, ConfigurationManager inherently caches all values. – Michaelamichaele

@TeomanSoygul RefreshSectioncall updates value retrieved through the ConfigurationManager.AppSettings[] it does not affect a Configuration instance. – Hist

Answer 2

If you process the configuration manually (perhaps not even in the app.config file), then you can periodically check that file for updates.

FileSystemWatcher is... probably overkill, and isn't guaranteed in all scenarios. Personally, I'd just poll the file every (say) 30 seconds.

Benz

Hi, do you mean pooling using solution described by @Teoman Soygul. I thing reloading that setting every 1 minute would satisfy my needs. – Sensillum

@Sensillum well, sort of; although I might not necessarily use the app-config path for it. Any route will work though; this doesn't need to be complex. – Benz

Answer 3

Simply refresh the "appSettings" from current config file before you read the value:

ConfigurationManager.RefreshSection("appSettings"); // Reload app settings from config file
ConfigurationManager.AppSettings["myKey"];          // Read the value as usually

No need to over complicate it by creating another config or configuration or what so ever suggested in your question or other answers!

Specter