ILog.cs / Log.cs - NLog service wrapper

ExampleBase.cs

using System;
using System.Threading;
using NLog;
using App.Diagnostics;

namespace App {

    public abstract class ExampleBase {
        private static readonly Lazy<ILogger> GenericLogger = new Lazy<ILogger>(LogManager.GetCurrentClassLogger, LazyThreadSafetyMode.PublicationOnly);
        protected ILog Log { get; private set; }


        /// <summary>
        /// Optionally allows subclasses to pass in an NLog ILogger instance or will otherwise use the Lazy initialized static logger for this class
        /// </summary>
        /// <param name="logger">An NLog ILogger class instance.</param>
        protected ExampleBase(ILogger logger = null) { Log = new Log(logger ?? GenericLogger.Value); }
    }

}

ExampleConcrete.cs

using NLog;
using App.Diagnostics;

namespace App {
    public abstract class ExampleConcrete : ExampleBase {
        public ExampleConcrete() : base(LogManager.GetCurrentClassLogger()) {
            // This will only execute the log message when LogLevel debugging is enabled in NLog config.
            Log.Debug(() => "Constructed!!!");
        }
    }
}

ILog.cs

using System;
using System.Runtime.CompilerServices;

namespace App.Diagnostics {
    public interface ILog {
        /// <summary>
        /// Records trace info if enabled.  Accepts an optional operation that returns a string message to save processing if trace logging is disabled. Ignore the other parameters, they are received by reflection.
        /// </summary>
        void Trace(Func<string> message = null, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = 0);

        /// <summary>
        /// Records debug info if enabled.  Accepts an optional operation that returns a string message to save processing if debug logging is disabled. Ignore the other parameters, they are received by reflection.
        /// </summary>
        void Debug(Func<string> message = null, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = 0);

        /// <summary>
        /// Records info if enabled.  Accepts an optional operation that returns a string message to save processing if info logging is disabled. Ignore the other parameters, they are received by reflection.
        /// </summary>
        void Info(Func<string> message = null, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = 0);

        /// <summary>
        /// Records warn info if enabled.  Accepts an operation that returns a string message to save processing if warn logging is disabled. Ignore the other parameters, they are received by reflection.
        /// </summary>
        void Warn(Func<string> message, Exception ex = null, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = 0);

        /// <summary>
        /// Records warn info if enabled for an exception. Ignore the parameters, they are received by reflection.
        /// </summary>
        void Warn(Exception ex, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = 0);

        /// <summary>
        /// Records error info if enabled.  Accepts an operation that returns a string message to save processing if error logging is disabled. Ignore the other parameters, they are received by reflection.
        /// </summary>
        void Error(Func<string> message, Exception ex = null, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = 0);

        /// <summary>
        /// Records error info if enabled for an exception.  Ignore the parameters, they are received by reflection.
        /// </summary>
        void Error(Exception ex, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = 0);

        /// <summary>
        /// Records fatal info if enabled.  Accepts an operation that returns a string message to save processing if fatal logging is disabled. Ignore the other parameters, they are received by reflection.
        /// </summary>
        void Fatal(Func<string> message, Exception ex, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = 0);

        /// <summary>
        /// Records fatal info if enabled for an exception.  Ignore the parameters, they are received by reflection.
        /// </summary>
        void Fatal(Exception ex, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = 0);
    }
}

Log.cs

using System;
using System.Runtime.CompilerServices;
using NLog;

namespace App.Diagnostics {
    public class Log : ILog {
        private readonly ILogger _logger;
        public Log(ILogger logger) { _logger = logger; }

        public void Trace(Func<string> message = null, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = default(int)) {
            if (_logger.IsTraceEnabled) _logger.Trace(FormatLog(message?.Invoke(), memberName, filePath, lineNumber));
        }

        public void Debug(Func<string> message = null, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = default(int)) {
            if (_logger.IsDebugEnabled) _logger.Debug(FormatLog(message?.Invoke(), memberName, filePath, lineNumber));
        }

        public void Info(Func<string> message = null, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = default(int)) {
            if (_logger.IsInfoEnabled) _logger.Info(FormatLog(message?.Invoke(), memberName, filePath, lineNumber));
        }

        public void Warn(Func<string> message, Exception ex = null, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = default(int)) {
            if (_logger.IsWarnEnabled) _logger.Warn(ex, FormatLog(message(), memberName, filePath, lineNumber));
        }

        public void Warn(Exception ex, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = default(int)) {
            if (_logger.IsWarnEnabled) _logger.Warn(ex, FormatLog(null, memberName, filePath, lineNumber));
        }

        public void Error(Func<string> message, Exception ex = null, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = default(int)) {
            if (_logger.IsErrorEnabled) _logger.Error(ex, FormatLog(message(), memberName, filePath, lineNumber));
        }

        public void Error(Exception ex, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = default(int)) {
            if (_logger.IsErrorEnabled) _logger.Error(ex, FormatLog(null, memberName, filePath, lineNumber));
        }

        public void Fatal(Func<string> message, Exception ex, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = default(int)) {
            if (_logger.IsFatalEnabled) _logger.Fatal(ex, FormatLog(message(), memberName, filePath, lineNumber));
        }

        public void Fatal(Exception ex, [CallerMemberName] string memberName = null, [CallerFilePath] string filePath = null, [CallerLineNumber] int lineNumber = default(int)) {
            if (_logger.IsFatalEnabled) _logger.Fatal(ex, FormatLog(null, memberName, filePath, lineNumber));
        }

        /// <summary>
        /// Can be overridden to allow specification of a custom log format.
        /// </summary>
        protected virtual string FormatLog(string message, string memberName = null, string filePath = null, int lineNumber = default(int))
            => $"{(message == null ? string.Empty : $"{message} | ")}Member => {memberName} | FilePath => {filePath} | LineNumber => {lineNumber}";
    }
}