When are settings from app.config actually read?

Question

When are settings from app.config actually read by application?

Suppose I have a windows service and some app settings for it. In code I have a method where some setting is used. Method is being called in every iteration, not just once during all the time. If I change the setting value through the configuration file should I restart the service for it to be "refreshed" inside or will it be accepted the next time without any interaction from my side?

Answer 1

You need to call ConfigurationManager.RefreshSection method to get the latest values read directly from disk. Here's a simple way to test and provide answer to your question:

static void Main(string[] args)
{
    while (true)
    {
        // There is no need to restart you application to get latest values.
        // Calling this method forces the reading of the setting directly from the config.
        ConfigurationManager.RefreshSection("appSettings");
        Console.WriteLine(ConfigurationManager.AppSettings["myKey"]);

        // Or if you're using the Settings class.
        Properties.Settings.Default.Reload();
        Console.WriteLine(Properties.Settings.Default.MyTestSetting);

        // Sleep to have time to change the setting and verify.
        Thread.Sleep(10000);
    }
}

My app.config containing:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <sectionGroup name="userSettings" type="System.Configuration.UserSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >
      <section name="ConsoleApplication2.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" allowExeDefinition="MachineToLocalUser" requirePermission="false" />
    </sectionGroup>
  </configSections>
  <appSettings>
    <add key="myKey" value="Original Value"/>
  </appSettings>
  <userSettings>
    <ConsoleApplication2.Properties.Settings>
      <setting name="MyTestSetting" serializeAs="String">
        <value>Original Value</value>
      </setting>
    </ConsoleApplication2.Properties.Settings>
  </userSettings>
</configuration>

After you start the application, open the app.config within the build folder, and change the value of the appSetting "myKey". You'll see the new value printed out to the console.

To answer the question, yes they are cached on the first time they are each read I think, and to force the read straight from the disk, you need to refresh the section.