如何将值注入NLog.config？

Question

I use a NLog.config, but some values I want to change from outside. Eg target:adress could change so I want to set it each time the software starts.

I imagine some thing like

var logger = new LoggerFactory().AddNLog().CreateLogger<Program>();
logger.target.adress = "myNewAdress";

How can I set values to my NLog.config?

Answer 1

You could edit the config in C# like this:

var configuration = LogManager.Configuration;
var fileTarget = configuration.FindTargetByName<FileTarget>("myTargetName");
fileTarget.FileName = "${basedir}/file.log";
LogManager.Configuration = configuration; //apply

Please note that combining the config file (nlog.config) and changing it in code, the reload of nlog.config could undo your changes. If you combine both, then reapply the changes on the reload event. Eg

public void UpdateConfig()
{
    var configuration = LogManager.Configuration;
    var fileTarget = configuration.FindTargetByName<FileTarget>("myTargetName");
    fileTarget.FileName = "${basedir}/file.log";
    LogManager.Configuration = configuration; //apply
}

// On start of your program
UpdateConfig();

LogManager.ConfigurationReloaded += (sender, e) =>
{
    //Re apply if config reloaded
    UpdateConfig();
};

See also: https://github.com/NLog/NLog/wiki/Configure-from-code

Answer 2

I recommend that one makes use of the NLog context layoutrenderers instead of modifying target properties at runtime. It ofcourse requires that the target-property supports NLog Layout.

Example of NLog.config:

<nlog>
    <targets>
       <target type="file" name="file" fileName="${gdc:item=LogDir}\LogFile.txt}" />
    </targets>
    <rules>
       <logger minLevel="Trace" writeTo="file" />
    </rules>
</nlog>

Then at runtime you can change the GDC-variables:

NLog.GlobalDiagnosticsContext.Set("LogDir", "C:\\Temp");

${gdc} Can also be combined with WhenEmpty , so one can provide a fallback default value, when nothing has been asigned from code.

See also: https://github.com/NLog/NLog/wiki/LogEvent-Context-Information