How to configure nlog to use IHostingEnvironment.ContentRootPath in FileTarget

Question

I am trying to add NLog for my asp.net core application. So I configured it exactly as described here https://github.com/NLog/NLog.Extensions.Logging . Also I added https://github.com/NLog/NLog.Web with default configuration too. So far so good, everything working as expected.

Now I want to store my log files not in harcoded folder specified in example c:\temp\nlog-own-${shortdate}.log but in folder which depends on current project. In my previous ASP.NET project I used something like this ${basedir}\App_Data\Logs\nlog-own-${shortdate}.log. Now It is also worked but placed files in bin directory. But I want to configure to place those files in IHostingEnvironment.ContentRootPath folder. Basically I want something like this

    private static Logger Logger = LogManager.GetCurrentClassLogger();
    private IHostingEnvironment _HostingEnvironment;
    public UserController(IHostingEnvironment env)
    {
        _HostingEnvironment = env;
    }

    public IActionResult Index()
    {
        var fileTarget = Logger.Factory.Configuration.FindTargetByName<NLog.Targets.FileTarget>("ownFile-web");
        fileTarget.FileName = new SimpleLayout(
            @"${basedir}\App_Data\Logs\nlog-own-${shortdate}.log"
                .Replace("${basedir}", _HostingEnvironment.ContentRootPath)
        );
        Logger.Info("Index page says hello");

        return View(new UserListArgs());
    }

but in more elegant way.

Answer 1

Something like this:

Update: in NLog 4.4 this is possible in one line (LayoutRenderer.Register)

Since NLog 4.4

public void Configure(IApplicationBuilder app, IHostingEnvironment env, 
                      ILoggerFactory loggerFactory)
{

    //add NLog to ASP.NET Core
    loggerFactory.AddNLog(); 

    //needed for non-NETSTANDARD platforms: configure nlog.config in your project root
    env.ConfigureNLog("nlog.config");

    LayoutRenderer.Register("basedir", (logEvent) => env.ContentRootPath);

    ...
 }

Before NLog 4.4

[LayoutRenderer("basedir")]
public class AspNetCoreBaseDirLayoutRenderer : LayoutRenderer
{
    public static IHostingEnvironment Env {get;set;}

    protected override void Append(StringBuilder builder, LogEventInfo logEvent)
    {
        builder.Append(env.ContentRootPath);
    }
}

Register:

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
  {
      //add NLog to ASP.NET Core
      loggerFactory.AddNLog();


      //needed for non-NETSTANDARD platforms: configure nlog.config in your project root
      env.ConfigureNLog("nlog.config");
      ...

      //overwrite ${basedir}
      AspNetCoreBaseDirLayoutRenderer.Env = env;
      ConfigurationItemFactory.Default.LayoutRenderers
          .RegisterDefinition("basedir", typeof(AspNetCoreBaseDirLayoutRenderer ));
      ...