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?

mservidio · Accepted Answer · 2012-02-08T18:31:05.870

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.

And if I get setting like this: Properties.Settings.Default.MyValue? — 26071986, Feb 08 '12 at 18:17
@26071986 - I'ved updated my answer to reflect the code for when using the Settings class. — mservidio, Feb 08 '12 at 18:25
As a note for those testing this, _on my machine_ this only works without the debugger attached. — Austin Salonen, Mar 27 '12 at 16:46

Bronumski · Answer 2 · 2012-02-08T17:58:36.760

Either when you load it up via the configuration manager (ConfigurationManager.GetSection("x/y");) or when you try to access the properties.

There is a slight grey area here because when you get the configuration out via the config manager:

var config = (MyConfigSection)ConfigurationManager.GetSection("MyConfigSection");

You get a configuration object back if you have provided the configuration section type in the configurationSections element at the top of the config file. If you do not actually provide the actual config you will still get an object back.

However if you have a required field that is not set it will not throw an exception till you call the property. I have worked this out whilst trying to unit test my custom configuration sections.

When are settings from app.config actually read?

2 Answers2

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