Dependency Injection wth NLog

Question

I\'ve got a .NET Core web app that I\'m trying to add logging to via NLog. In previous projects, I\'ve just used something like the following at the top of every class:

Answer 1

I think I've figured out an acceptable solution, although not exactly the way I asked the question.

First of all, I create a "LoggerFactory", which has a single method called "GetLogger" (which creates the concrete NLog Logger and accepts a class name as a parameter), and I inject this factory instead of the logger directly.

LoggerFactory:

public class LoggerFactory : ILoggerFactory
{
    public ILogger GetLogger(string fullyQualifiedClassName)
    {
        return new NLogLogger(fullyQualifiedClassName);
    }
}

NLogLogger:

public class NLogLogger : ILogger, INLogLogger
{
    NLog.Logger mylogger;
    public NLogLogger(string fullyQualifiedClassName)
    {
        mylogger = NLog.LogManager.GetLogger(fullyQualifiedClassName);
    }
}

Startup.cs:

services.AddScoped<BLL.Logging.ILoggerFactory>();

The in my controller class, I've got:

    private BLL.Logging.ILogger logger;//my NLogLogger inherits this interface

    public HomeController(BLL.Logging.ILoggerFactory loggerFactory)
    {
        logger = loggerFactory.GetLogger(this.GetType().FullName);
    }

So what I've effectively now done, is rather than injecting the actual Logger itself (Which @Steven indicated would not be possible the way I was trying to do it), I've instead injected the utility to create an instance of a logger which wraps NLog.

I've still got the responsibility to create the logger within the class, but at least I've decoupled from the underlying logging framework (NLog).

Answer 2

Using DI specify ILogger<T> type instead of Logger, where T is the class type that uses the logger, so NLog will know about the class. For example:

public class TodoController : Controller
{
    private readonly ILogger _logger;

    public TodoController(ILogger<TodoController> logger)
    {
        _logger = logger;
    }
}

References:

• Getting started with ASP.NET Core (csproj vs2017)
• Getting started with ASP.NET Core 2
• Getting started with ASP.NET Core 3