DotNet Core Console 程式使用NLog

參考：https://github.com/NLog/NLog/wiki/Tutorial

步驟：

1. 使用Nuget安裝NLog.Extensions.Logging

Install-Package NLog.Extensions.Logging

2.編寫代碼（到這步運行代碼，不報錯，但是也不會有log輸出，因為沒有設置配置文件）

3. 編寫配置文件

   在項目下新增加NLog.config 文件，並設置其能copy到運行目錄。將一下內容粘到裡面，重新運行程式就可以看到輸出到file.txt的log.

    <?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">
    
      <targets>
        <target name="logfile" xsi:type="File" fileName="file.txt" />
      </targets>
    
      <rules>
        <logger name="*" minlevel="Info" writeTo="logfile" />
      </rules>
</nlog>

4. 增加輸出源，將Log輸出到屏幕上,按照以下內容對配置文件做修改

    <?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">
    
      <targets>
        <target name="logfile" xsi:type="File" fileName="file.txt" />
        <target name="console" xsi:type="Console" />
      </targets>
    
      <rules>
        <logger name="*" minlevel="Info" writeTo="logfile" />
        <logger name="*" minlevel="Info" writeTo="console" />
      </rules>
</nlog>

5. 如果想發送郵件，可以安裝NLog.MailKit

Install-Package NLog.MailKit

6.在配置文件中添加發送郵件的設置部分（參考https://github.com/nlog/NLog/wiki/Mail-target）

    <?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"
          internalLogFile="d:\Nlog_log.txt" internalLogLevel="Error">
      <variable name="smtpServer" value="***"/>
      <variable name="smtpUserName" value="***"/>
      <variable name="smtpPassword" value="***"/>
      <variable name="from" value="***"/>
      <variable name="to" value="***"/>
    
      <targets>
        <target name="logfile" xsi:type="File" fileName="logs\${date:format=yyyyMMdd}_log.txt" layout="${date:format=yyyy-MM-dd HH\:mm\:ss} ${message}" />
        <target name="console" xsi:type="Console" layout="${date:format=yyyy-MM-dd HH\:mm\:ss} [${level}] ${message}"/>
        <target name="infoMail" xsi:type="Mail"
                  smtpServer="${smtpServer}"
                  smtpUserName="${smtpUserName}"
                  smtpPassword="${smtpPassword}"
                  from="${from}"
                  to="${to}"
                  subject="info log"
                  body="${message}"
                  html="true"/>
        <target name="errorMail" xsi:type="Mail"
                  smtpServer="${smtpServer}"
                  smtpUserName="${smtpUserName}"
                  smtpPassword="${smtpPassword}"
                  from="${from}"
                  to="${to}"
                  subject="error log"
                  body="${message}"/>
      </targets>
    
      <rules>
        <logger name="***" minlevel="Info" writeTo="infoMail" />
        <logger name="***" minlevel="Error" writeTo="logfile" />
        <logger name="Main" minlevel="Info" writeTo="console" />
        <logger name="Main" minlevel="Error" writeTo="errorMail" />
      </rules>
    
      <extensions>
        <add assembly="NLog.MailKit"/>
      </extensions>
</nlog>