static void

NLog logging

Github Wiki

Log writing

class Program
{
    private static readonly Logger Logger = LogManager.GetCurrentClassLogger();

    static void Main()
    {
        var x = 1;
        Logger.Warn("Danger, Will Robinson!");
        Logger.Error("Danger, {0}!", x);
        try
        {
            throw new InvalidOperationException("Oops");
        }
        catch (InvalidOperationException ex)
        {
            Logger.Error(ex, "Exception logged");
        }
    }
}

Logging Traces

Many libraries log to Trace:
System.Diagnostics.Trace.TraceWarning("Danger!");
It's nice not to take a dependency on logging when people have different preferences.

NLog includes a trace listener, so just hook it up in web/app.config

<configuration>
  <system.diagnostics>
    <trace autoflush="true">
      <listeners>
        <add name="MyNLogTraceListener" type="NLog.NLogTraceListener, NLog" />
      </listeners>
    </trace>
  </system.diagnostics>
</configuration>

The only limitation is the layout ${logger} symbol is just the executing assembly, not the class where logging occurred. Not a great problem, as you may be more specific in your ${message}: Trace.TraceInformation("Runner.Run started")

NLog.config

You can configure in the app/web.config but creating a NLog.config is the most common strategy.

Simple

<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      autoReload="true">
  <targets>
    <target name="logfile"
            xsi:type="File"
            fileName="../logs/file.txt"
            layout="${longdate} ${pad:padding=5:inner=${level}} ${logger} ${message} ${exception:format=tostring}"
            />
  </targets>
  <rules>
    
    <logger name="*" minlevel="Warn" writeTo="logfile" />
  </rules>
</nlog>

autoReload="true" - changing the file will immediately reload this config
<logger takes all sources (*) with a minimum level (order: Trace, Debug, Info, Warn, Error, Fatal) and sends them to named logger.
<target is xsi:type="File" (as opposed to console or email etc)
layout contains $() tokens. For date/time, ${longdate} seems best. It's useful to have ${message} AND ${exception:format=tostring} if you log an exception object

Multiple rules and targets

<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      autoReload="true">
  <targets>
    <target name="console" xsi:type="Console" />
    <target name="testconsolefile" xsi:type="File" fileName="testconsolefile.txt" />
    <target name="logfile"
            xsi:type="File"
            fileName="../logs/file.txt"
            layout="${longdate} ${pad:padding=5:inner=${level}} ${logger} ${message} ${exception:format=tostring}"
            />
  </targets>
  <rules>
    <logger name="*" minlevel="Warn" writeTo="logfile" />
    
    <logger name="TestConsole.*" minlevel="Debug" writeTo="testconsolefile" />
  </rules>
</nlog>

Rolling Files

<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      autoReload="true">
  <targets async="true">
    <target name="logfile"
            xsi:type="File"
            fileName="../logs/file.log"
            layout="${longdate} ${pad:padding=5:inner=${level}} ${logger} ${message} ${exception:format=tostring}"
            archiveFileName="../logs/file.{#}.log"
            archiveEvery="Day"
            archiveNumbering="Sequence"
            archiveDateFormat="yyyyMMdd"
            maxArchiveFiles="14"
            />
  </targets>
  <rules>
    <logger name="*" minlevel="Warn" writeTo="logfile" />
  </rules>
</nlog>

<targets async="true"> creates an "AsyncWrapper" implicitly, so log writes are async and buffered.
Like the log4net's RollingFileAppender
- By size:- archiveAboveSize="1048576" = 1Mb
- By time:- archiveEvery="Day"
- archiveNumbering="Sequence" or Date or DateAndSequence
- Rolling over is slow
- maxArchiveFiles is default 9