使用NLog.Extensions.Logging（1.6.1）打印多行消息

Question

我正在使用NLog.Extensions.Logging（v1.6.1）开发一个.NET Core 3.1控制台应用程序，并希望打印一条包含多行的消息。我遵循了以前在StackOverflow上提供的一个示例，该示例使用包装器布局渲染器，复制如下。我看到了如何替换新行；但是，多行消息的开头（即第一行）未加前缀（？）

示例的输出看起来像这样：

line 1> Hello world 
line 2> 19:30:45.2313 Hello World , again

先前提供的示例代码：

using System;
using System.Text;
using NLog.Config;
using NLog.LayoutRenderers;
using NLog.LayoutRenderers.Wrappers;
using NLog.Layouts;

namespace My.Namespace
{
    [LayoutRenderer("replace-newlines-withlayout")]
    [ThreadAgnostic]
    public class ReplaceNewLinesFormatLayoutRendererWrapper : WrapperLayoutRendererBase
    {
        private string m_replacementString = " ";

        public ReplaceNewLinesFormatLayoutRendererWrapper()
        {
            // Changed from
            // Replacement = " ";
            Replacement = Layout.FromString(" ");
        }

        // Changed from
        // public string Replacement { get; set; }
        public Layout Replacement { get; set; }

        // Override Append in order to render the replacement.
        protected override void  Append(StringBuilder builder, NLog.LogEventInfo logEvent)
        {
            // Render...
            m_replacementString = Replacement.Render(logEvent);

            // The base functionality of append is fine.
            base.Append(builder, logEvent);
        }   

        // Called from base.Append()
        protected override string Transform(string text)
        {
            // Changed from 
            // return text.Replace(Environment.NewLine, Replacement);

            // Now just put in the rendered replacement string.
            return text.Replace(Environment.NewLine, m_replacementString);
        }
    }
}

NLog.Config

<?xml version="1.0" encoding="utf-8" ?>
<!-- XSD manual extracted from package NLog.Schema: https://www.nuget.org/packages/NLog.Schema-->
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xsi:schemaLocation="NLog NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      autoReload="true"
      internalLogFile="c:\temp\console-example-internal.log"
      internalLogLevel="Info" >

  <!-- the targets to write to -->
  <targets>
    <!-- write logs to file -->
    <target xsi:type="File" name="target1" fileName="c:\temp\console-example.log"
        layout="${replace-newlines-withlayout:replacement=${newline}${time}:${message}}" />
    <target xsi:type="ColoredConsole" name="target2"
        layout="${replace-newlines-withlayout:replacement=${newline}${time}:${message}}" />
    />
  </targets>

  <!-- rules to map from logger name to target -->
  <rules>
    <logger name="*" minlevel="Trace" writeTo="target1,target2" />
  </rules>
</nlog>

示例：

class Program
{
    private static readonly NLog.Logger Logger = NLog.LogManager.GetCurrentClassLogger();

    static void Main(string[] args)
    {
        try
        {
            var ReplaceNewLinesFormatLayoutRendererWrapper = new ReplaceNewLinesFormatLayoutRendererWrapper();
            ReplaceNewLinesFormatLayoutRendererWrapper.Register<NLogTest.ReplaceNewLinesFormatLayoutRendererWrapper>("replace-newlines-withlayout");

            Logger.Info($"Hello world {Environment.NewLine} Hello World , again");
            System.Console.ReadKey();
        }
        catch (Exception ex)
        {
            Logger.Error(ex, "yeah, here again");
        }
    }
}

Answer 1

这里的问题是Transform在Append之前被调用，而您的Transform依赖于Append。

幸运的是，现在有一个更好的Transform可以覆盖，该参数还将包含LogEventInfo作为参数。 （NLog 4.5 +）

因此您可以删除当前的Append和Transform覆盖，并替换为：

protected override string Transform(LogEventInfo logEvent, string text)
{
    // Render...
    var replacementString = Replacement.Render(logEvent);

    // Now just put in the rendered replacement string.
    return text.Replace(Environment.NewLine, replacementString);
}

完整代码（经过一些清洁）：

using System;
using NLog;
using NLog.Config;
using NLog.LayoutRenderers;
using NLog.LayoutRenderers.Wrappers;
using NLog.Layouts;

namespace My.Namespace
{
    [LayoutRenderer("replace-newlines-withlayout")]
    [ThreadAgnostic]
    public class ReplaceNewLinesFormatLayoutRendererWrapper : WrapperLayoutRendererBase
    {
        public Layout Replacement { get; set; } = " ";

        protected override string Transform(LogEventInfo logEvent, string text)
        {
            // Render...
            var replacementString = Replacement.Render(logEvent);

            // Now just put in the rendered replacement string.
            return text.Replace(Environment.NewLine, replacementString);
        }
    }
}