https://www.cnblogs.com/lzrabbit/archive/2012/03/23/2413180.html
https://blog.csdn.net/guyswj/article/details/81940188

一、引用log4net
二、在AssemblyInfo.cs中添加

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

三、新增配置文件log4net.config

<?xml version="1.0" encoding="utf-8"?>

<configuration>
  <configSections>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net"/>
  </configSections>
  <log4net debug="true">
    <appender name="ErrorAppender" type="log4net.Appender.RollingFileAppender">
      <!--日志路径-->
      <param name="File" value="bin\\log\\logError\\" />
      <!--是否向文件中追加日志-->
      <param name="AppendToFile" value="true" />
      <!--按照何种方式产生多个日志文件(日期[Date],文件大小[Size],混合[Composite])-->
      <param name="RollingStyle" value="Composite" />
      <!--日志文件名格式为:2008-08-31.log-->
      <param name="DatePattern" value="yyyy-MM-dd&quot;.log&quot;" />
      <!--日志保留天数-->
      <param name="MaxSizeRollBackups" value="20" />
      <!--每个文件的大小。只在混合方式与文件大小方式下使用。超出大小后在所有文件名后自动增加正整数重新命名，数字最大的最早写入。可用的单位:KB|MB|GB。不要使用小数,否则会一直写入当前日志-->
      <param name="MaximumFileSize" value="1024KB" />
      <!--日志文件名是否是固定不变的-->
      <param name="StaticLogFileName" value="false" />
      <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
      <layout type="log4net.Layout.PatternLayout">
        <param name="ConversionPattern" value="%d %p %m "/>
      </layout>
    </appender>
    <appender name="InfoAppender" type="log4net.Appender.RollingFileAppender">
      <param name="File" value="bin\\log\\logInfo\\" />
      <param name="AppendToFile" value="true" />
      <param name="RollingStyle" value="Date" />
      <param name="DatePattern" value="yyyy-MM-dd&quot;.log&quot;" />
      <param name="MaxSizeRollBackups" value="20" />
      <param name="MaximumFileSize" value="1024KB" />
      <param name="StaticLogFileName" value="false" />
      <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
      <layout type="log4net.Layout.PatternLayout">
        <param name="ConversionPattern" value="%d %m %n"  />
      </layout>
    </appender>
    <logger name="logerror">
      <level value="ALL" />
      <appender-ref ref="ErrorAppender" />
    </logger>
    <logger name="loginfo">
      <level value="ALL" />
      <appender-ref ref="InfoAppender" />
    </logger>
  </log4net>
</configuration>

四、封装LogHelper类

public class LogHelper
{
    public readonly log4net.ILog loginfo = log4net.LogManager.GetLogger("loginfo");
    public readonly log4net.ILog logerror = log4net.LogManager.GetLogger("logerror");

    public void Info(string msg)
    {
        if (loginfo.IsInfoEnabled)
        {
        loginfo.Info(msg);
        }
    }

    public void Error(string msg, Exception e)
    {
        if (logerror.IsErrorEnabled)
        {
        logerror.Error(msg, e);
        }
    }
    //public void Debug(string msg, Exception e)
    //{
    //    //if (logdebug.IsErrorEnabled)
    //    //{
    //    logerror.Debug(msg, e);
    //    //}
    //}
}

五、调用示例

LogHelper logHelper = new LogHelper();
logHelper.Info(string.Format("当前的时间{0}", DateTime.Now.ToString()));
logHelper.Error("errorakkpkey", new Exception("log4net测试致命信息"));