1. 在 App.config 文件 增加

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <configSections>
        <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
    </configSections>
    <log4net>
        <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
            <param name="Encoding" value="utf-8"/>
            <file value="Log\\"/>
            <appendToFile value="true"/>
            <rollingStyle value="Date"/>
            <datePattern value="yyyyMMdd'.log'"/>
            <staticLogFileName value="false"/>
            <layout type="log4net.Layout.PatternLayout">
                <conversionPattern value="%date [%thread] %-5level %logger - %message%newline"/>
            </layout>
        </appender>
        <root>
            <level value="DEBUG"/>
            <appender-ref ref="RollingLogFileAppender"/>
        </root>
    </log4net>
</configuration>

2. 在 AssemblyInfo.cs 增加

[assembly: log4net.Config.XmlConfigurator(Watch = true)]

3. 在类中增加

public static readonly ILog log = LogManager.GetLogger(typeof(UrlWatchManagerWindow));

4. 参考 Apache log4net™ Manual – Configuration