NLog load configuration from both file and code

I'm using NLog 4.7.2. I would like to configure it from code. However, I would like to retain the possibility to modify logging configuration without having to restart my application. I know I could roll something on my own (for instance, a switch on the UI that would modify the appropiate rules and call LogManager.ReconfigExistingLoggers()) but I would like to take advantadge of the existing functionality of XML configuration file autoreload.

My intention is to make a default configuration in code and then if something pops up and I need to increase the logging level, I would modify the XML configuration file without restarting the application.

Solution

Updated answer

If using a NLog.config like this:

<nlog autoreload="true" keepVariablesOnReload="true">
   <variable name="AppMinLevel" value="Warn" />
   <targets>
   </targets>
   <rules>
      <logger name="*" minLevel="${var:AppMinLevel}" writeTo="..." />
   </rules>
</nlog>

Then by referencing ${var:AppMinLevel} in the logging-rule, then you can just update the NLog config variable like this:

NLog.LogManager.Variables["AppMinLevel"] = "Debug";
LogManager.ReconfigExistingLoggers();

Old Answer

If using a NLog.config like this:

<nlog autoreload="true">
   <variable name="minlevel" value="Warn" />
</nlog>

Then perform initial setup of LoggingConfiguration like this:

SetupNLogConfig();
LogManager.ConfigurationReloaded += (sender, args) => {
   SetupNLogConfig();
}

And have SetupNLogConfig like this:

void SetupNLogConfig()
{
     var config = LogManager.Configuration ?? new NLog.Config.LoggingConfiguration();
     Layout minLevel = config.Variables["minlevel"] ?? "Warn";
     string minLevelString = minLevel.Render(LogEventInfo.CreateNullEvent());
     LogLevel minLevelValue = LogLevel.FromString(minLevelString);

     // Targets where to log to: File and Console
     var logfile = new NLog.Targets.FileTarget("logfile") { FileName = "file.txt" };
     var logconsole = new NLog.Targets.ConsoleTarget("logconsole");
        
     // Rules for mapping loggers to targets            
     config.AddRule(minLevelValue, LogLevel.Fatal, logconsole);
     config.AddRule(minLevelValue, LogLevel.Fatal, logfile);
        
     // Re-Apply config           
     NLog.LogManager.Configuration = config;
}

Then you can modify the minlevel-variable in NLog.config and it should re-configure with the updated value.