How do I retrieve AppSettings from the assembly config file?

Question

I would like to retrieve the AppSetting key from the assembly config file called: MyAssembly.dll.config. Here's a sample of the config file:

<configuration>
    <appSettings>
        <add key="MyKey" value="MyVal"/>
    </appSettings>
</configuration>

Here's the code to retrieve it:

var myKey = ConfigurationManager.AppSettings["MyKey"];

Answer 1

Using the OpenMappedExeConfiguration gives you back a "Configuration" object which you can use to peek into the class library's config (and the settings that exist there will override the ones by the same name in the main app's config):

ExeConfigurationFileMap map = new ExeConfigurationFileMap();
map.ExeConfigFilename = "ConfigLibrary.config";

Configuration libConfig = ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None);

AppSettingsSection section = (libConfig.GetSection("appSettings") as AppSettingsSection);
value = section.Settings["Test"].Value;

But those settings that are unique to the main app's config and do not exist in the class library's own config are still accessible via the ConfigurationManager static class:

string serial = ConfigurationManager.AppSettings["Serial"];

That still works - the class library's config only hides those settings that are inside its config file; plus you need to use the "libConfig instance to get access to the class library's own config settings, too .

The two worlds (main app.config, classlibrary.config) can totally and very happily co-exist - not a problem there at all!

Marc