1，引用Log4Net.dll 。當前為2.0.8.0版，可添加Nuget包。我的辦法是從下載的包中直接引用相應.net版本的dll以減小項目體積

2，在App.config中增加<log4net>節,內容為：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
    </startup>
  <
 
log4net>
    <logger name="logerror">
      <level value="ERROR" />
      <appender-ref ref="ErrorAppender" />
    </logger>
    <logger name="loginfo">
      <level value="INFO" />
      <appender-ref ref="InfoAppender" />
    </logger>
    <appender 
 
name="ErrorAppender" type="log4net.Appender.RollingFileAppender">
      <param name="File" value="Log\\LogError\\" />
      <param name="AppendToFile" value="true" />
      <param name="MaxSizeRollBackups" value="100" />
      <param name="MaxFileSize" value="10240" />
      <param 
 
name="StaticLogFileName" value="false" />
      <param name="DatePattern" value="yyyyMMdd&quot;.txt&quot;" />
      <param name="RollingStyle" value="Date" />
      <layout type="log4net.Layout.PatternLayout">
        <param name="ConversionPattern" value="%n異常時間：%d %n異常級別：%-5p%n異常內容：%m%n" />
      </layout>
      <!--&lt; &gt; = <> %n = 回車-->
    </appender>
    <appender name="InfoAppender" type="log4net.Appender.RollingFileAppender">
      <param name="File" value="Log\\LogInfo\\" />
      <param name="AppendToFile" value="true" />
      <param name="MaxFileSize" value="10240" />
      <param name="MaxSizeRollBackups" value="100" />
      <param name="StaticLogFileName" value="false" />
      <param name="DatePattern" value="yyyyMMdd&quot;.txt&quot;" />
      <param name="RollingStyle" value="Date" />
      <layout type="log4net.Layout.PatternLayout">
        <param name="ConversionPattern" value="日誌時間：%d %n日誌級別：%-5p  %n日誌內容：%m%n%n" />
      </layout>
    </appender>
  </log4net>
</configuration>

3，項目AssemblyInfo.cs文件中增加一行代碼，用以註冊log4net.config文件

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

4，項目中添加日誌類

 public class LogHelper
    {
        private LogHelper()
        {
        }

        public static readonly log4net.ILog loginfo = log4net.LogManager.GetLogger("loginfo");

        public static readonly log4net.ILog logerror = log4net.LogManager.GetLogger("logerror");

        public static void SetConfig()
        {
            log4net.Config.XmlConfigurator.Configure();
        }

        public static void SetConfig(FileInfo configFile)
        {
            log4net.Config.XmlConfigurator.Configure(configFile);
        }

        public static void WriteLog(string info)
        {
            if (loginfo.IsInfoEnabled)
            {
                loginfo.Info(info);
            }
        }

        public static void WriteLog(string info, Exception se)
        {
            if (logerror.IsErrorEnabled)
            {
                logerror.Error(info, se);
            }
        }
    }

5，測試

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TestLog4Net
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                LogHelper.WriteLog("程序啟動，正常記錄！");
                int a = Convert.ToInt32("zzz");
            }
            catch (Exception ex)
            {
                LogHelper.WriteLog("錯誤", ex);
            }
        }
    }
}

6，測試結果：運行目錄下生成log文件夾，其下兩個文件夾：LogError，LogInfo，其內是以日期為文件名的Txt日誌

Log4Net配置使用簡記