Hey Adam, I totally get your frustration—most modern logging tutorials fixate on .NET Core, but .NET Framework 4.7.1 still has robust, battle-tested logging options. Let’s break down the most practical approaches for your MVC 5 project:

Option 1: log4net (Widely Used & Flexible) #

log4net is a stalwart in .NET Framework logging, with tons of customization options. Here’s how to set it up:

1. Install the NuGet Package
   Open the Package Manager Console and run:

   Install-Package log4net
   

2. Add a log4net Configuration File
   Create a new file named log4net.config in your project root with this basic setup (adjust outputs as needed):

   <?xml version="1.0" encoding="utf-8" ?>
   <log4net>
     <appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender">
       <layout type="log4net.Layout.PatternLayout">
         <conversionPattern value="%date [%thread] %-5level %logger - %message%newline" />
       </layout>
     </appender>
     <appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
       <file value="logs/app.log" />
       <appendToFile value="true" />
       <rollingStyle value="Size" />
       <maxSizeRollBackups value="5" />
       <maximumFileSize value="10MB" />
       <staticLogFileName value="true" />
       <layout type="log4net.Layout.PatternLayout">
         <conversionPattern value="%date [%thread] %-5level %logger - %message%newline" />
       </layout>
     </appender>
     <root>
       <level value="INFO" />
       <appender-ref ref="ConsoleAppender" />
       <appender-ref ref="RollingFileAppender" />
     </root>
   </log4net>
   

   Don’t forget to set this file’s Copy to Output Directory property to "Copy if newer" (right-click the file → Properties).

3. Initialize log4net
   Add this line to your AssemblyInfo.cs (under Properties folder) to load the config on startup:

   [assembly: log4net.Config.XmlConfigurator(ConfigFile = "log4net.config", Watch = true)]
   

4. Use It in Controllers
   Inject the logger into your controller and start logging:

   using log4net;
   
   public class HomeController : Controller
   {
       private static readonly ILog _logger = LogManager.GetLogger(typeof(HomeController));
   
       public ActionResult Index()
       {
           _logger.Info("Home/Index page loaded");
           _logger.Warn("This is a warning message");
           _logger.Error("An error occurred!", new Exception("Sample exception"));
           return View();
       }
   }
   

Option 2: NLog (Lightweight & Easy to Configure) #

NLog is another popular choice with simple setup and great performance:

1. Install NuGet Packages
   Run these commands in the Package Manager Console:

   Install-Package NLog.Web
   Install-Package NLog.Config
   

2. Configure NLog
   The NLog.config file will be added automatically—tweak it to your needs (here’s a basic version):

   <?xml version="1.0" encoding="utf-8" ?>
   <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="file" xsi:type="File" fileName="logs/nlog-${shortdate}.log"
               layout="${longdate} ${level} ${message} ${exception:format=ToString}" />
     </targets>
   
     <rules>
       <logger name="*" minlevel="Info" writeTo="console,file" />
     </rules>
   </nlog>
   

   Again, set Copy to Output Directory to "Copy if newer".

3. Initialize NLog
   Update your Global.asax.cs Application_Start method:

   using NLog.Web;
   
   protected void Application_Start()
   {
       // Initialize NLog
       NLog.Web.NLogBuilder.ConfigureNLog("NLog.config");
       AreaRegistration.RegisterAllAreas();
       RouteConfig.RegisterRoutes(RouteTable.Routes);
       // ... other startup code
   }
   

4. Log in Controllers
   Use the logger like this:

   using NLog;
   
   public class HomeController : Controller
   {
       private static readonly Logger _logger = LogManager.GetCurrentClassLogger();
   
       public ActionResult Index()
       {
           _logger.Info("Home page accessed");
           _logger.Error("Error in Index action", new Exception("Test error"));
           return View();
       }
   }
   

Option 3: System.Diagnostics (No External Dependencies) #

If you don’t want to add third-party packages, use .NET’s built-in System.Diagnostics:

1. Configure Trace Listeners in Web.config
   Add this section to your Web.config to set up file logging:

   <system.diagnostics>
     <trace autoflush="true" indentsize="4">
       <listeners>
         <add name="fileListener" 
              type="System.Diagnostics.TextWriterTraceListener" 
              initializeData="logs/trace.log" />
         <remove name="Default" />
       </listeners>
     </trace>
   </system.diagnostics>
   

2. Log Messages
   Use Trace static methods in your controller:

   using System.Diagnostics;
   
   public class HomeController : Controller
   {
       public ActionResult Index()
       {
           Trace.TraceInformation("Index page loaded at {0}", DateTime.Now);
           Trace.TraceWarning("Low memory warning");
           Trace.TraceError("Critical error occurred!", new Exception("Sample exception"));
           return View();
       }
   }
   

   Note: You’ll need to manually create the logs folder in your output directory, or configure the listener to create it automatically.

Quick Tips #

• Always set configuration files to copy to the output directory—this is a common pitfall.
• Adjust log levels (Info, Warn, Error, Debug) based on your needs; Debug logs are great for development but should be turned off in production.
• For more advanced scenarios, you can integrate logging with dependency injection (using Unity, Autofac, etc.) to avoid static logger instances.

内容的提问来源于stack exchange，提问作者Adam