我和我的团队有一个Windows窗体应用程序，我正在将其从.NET Framework 4.6.2转换为.NET 6。我们通过Microsoft.Extensions.Logging使用NLog写入日志文件和主应用程序窗体上的RichTextBox。（软件包版本：NLog.Extensions.Logging 5.3.2/NLog.Windows.Forms 5.2.0）

<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" autoReload="true" throwExceptions="false" internalLogFile="${basedir}/LogFiles/InternalLog.txt" internalLogLevel="Info">
  <extensions>
    <add assembly="NLog.Windows.Forms"/>
  </extensions>
  <targets>
    <default-wrapper xsi:type="AsyncWrapper" timeToSleepBetweenBatches="500" />
    <target name="file" xsi:type="File" layout="${longdate}|${level}|${message}|${exception}" fileName="${basedir}/LogFiles/file.txt" archiveAboveSize="1048576" archiveEvery="Day" maxArchiveFiles="21" archiveFileName="${basedir}/LogFiles/Errorlog/file.{####}.txt" archiveNumbering="Sequence" encoding="utf-8"/>
    <target name="trace" xsi:type="Trace" layout="${longdate}|${level}|${message}|${exception}" />
    <target name="richTextBox" xsi:type="RichTextBox" layout="${message}${exception}" controlName="rtbStatus" formName="BaseForm" allowAccessoryFormCreation="false" messageRetention="All" maxLines="10000"/>
  </targets>
  <rules>
    <logger name="ErrorLog" minlevel="Info" writeTo="file,trace,richTextBox"/>
  </rules>
</nlog>

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表单本身用于配置和运行从许多其他应用程序接收消息的基础服务。对于用户配置通信的每个应用程序，我们也以编程方式创建FileTarget，以便生成可用于调试的模拟文件。这些附加目标设置如下：

public NLogSimFileLogger(string category, string name)
{
    try
    {
        this._TargetName                        = category + "-" + name;
        FileTarget target                       = new FileTarget();
        target.Layout                           = "${message}";
        target.ReplaceFileContentsOnEachWrite   = false;
        target.ArchiveAboveSize                 = 1048576;
        target.ArchiveEvery                     = FileArchivePeriod.Day;
        target.MaxArchiveFiles                  = 21;
        target.ArchiveFileName                  = "${basedir}/LogFiles/Sims/" + category + "/" + name + "{####}.txt";
        target.ArchiveNumbering                 = ArchiveNumberingMode.Sequence;
        target.FileName                         = "${basedir}/LogFiles/Sims/" + category + "/" + name + ".sim";
        target.KeepFileOpen                     = true;
        target.ConcurrentWrites                 = true;
        target.Name                             = this._TargetName;

        LogManager.Configuration.AddRule(LogLevel.Debug, LogLevel.Fatal, target, this._TargetName);
        LogManager.ReconfigExistingLoggers();

        this._Logger = LoggerFactory.Create(configure => configure.AddNLog(LogManager.Configuration)).CreateLogger(this._TargetName);
    }
    catch(Exception ex)
    {
        ...
    }
}

型
然而，当创建目标时，当试图从NLog. Windows. Forms. RichTextBox内部的SendTheMessageToRichTextBox方法访问TargetRichTextBox时，我们会获得System.NullReferenceException。

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
 ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at NLog.Windows.Forms.RichTextBoxTarget.SendTheMessageToRichTextBox(String logMessage, RichTextBoxRowColoringRule rule, LogEventInfo logEvent)
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle.InvokeMethod(Object target, Span`1& arguments, Signature sig, Boolean constructor, Boolean wrapExceptions)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at System.Delegate.DynamicInvokeImpl(Object[] args)
   at System.Delegate.DynamicInvoke(Object[] args)
   at System.Windows.Forms.Control.InvokeMarshaledCallbackDo(ThreadMethodEntry tme)
   at System.Windows.Forms.Control.InvokeMarshaledCallbackHelper(Object obj)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Forms.Control.InvokeMarshaledCallback(ThreadMethodEntry tme)
   at System.Windows.Forms.Control.InvokeMarshaledCallbacks()
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.TextBoxBase.WndProc(Message& m)
   at System.Windows.Forms.RichTextBox.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, WM msg, IntPtr wparam, IntPtr lparam)
   at Interop.User32.DispatchMessageW(MSG& msg)
   at System.Windows.Forms.Application.ComponentManager.Interop.Mso.IMsoComponentManager.FPushMessageLoop(UIntPtr dwComponentID, msoloop uReason, Void* pvLoopData)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(msoloop reason, ApplicationContext context)
   at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(msoloop reason, ApplicationContext context)
   at System.Windows.Forms.Application.Run(Form mainForm)
   at MyLibrary.SingleInstance..ctor(Form mainForm, SingleInstanceTypes type) in C:\SandBox\Libraries\UI\Lear.UI\SingleInstance.cs:line 104
   at MyApp.Program.Main(String[] args) in C:\Sandbox\LPS3Services\Projects\MessageRouter\LPS.MessageRouter.Monitor\Program.cs:line 38

型
下面是生成的内部日志。

2023-07-28 11:56:40.0448 Info Message Template Auto Format enabled
2023-07-28 11:56:40.0564 Info Loading assembly name: NLog.Windows.Forms
2023-07-28 11:56:40.0767 Info NLog.Windows.Forms, Version=5.0.0.0, Culture=neutral, PublicKeyToken=5120e14c03d0593c. File version: 5.2.0.532. Product version: 5.2.0+2d57aed1aadb6fc0d0ffaa67674ba6ad00baf4cd. GlobalAssemblyCache: False
2023-07-28 11:56:40.1461 Info Registered target NLog.Targets.Wrappers.AsyncTargetWrapper(Name=file)
2023-07-28 11:56:40.1461 Info Registered target NLog.Targets.Wrappers.AsyncTargetWrapper(Name=trace)
2023-07-28 11:56:40.1461 Error Forbidden usage of RetentionStrategy (All) when MaxLines is not set
2023-07-28 11:56:40.1461 Info Registered target NLog.Targets.Wrappers.AsyncTargetWrapper(Name=richTextBox)
2023-07-28 11:56:40.1849 Info Validating config: TargetNames=file, trace, richTextBox, ConfigItems=30, FilePath=.\MyApp\bin\Debug\net6.0-windows\NLog.config
2023-07-28 11:56:40.2046 Info Form BaseForm not found, waiting for ReInitializeAllTextboxes.
2023-07-28 11:56:40.2113 Info Configuration initialized.
2023-07-28 11:56:40.2113 Info NLog, Version=5.0.0.0, Culture=neutral, PublicKeyToken=5120e14c03d0593c. File version: 5.2.2.1914. Product version: 5.2.2+51cc02a2dd780a9a01eb6747de52071d78e2f506. GlobalAssemblyCache: False
2023-07-28 11:56:40.5062 Info Executing ReInitializeAllTextboxes for Form MyApp.MainForm, Text: MainForm
2023-07-28 11:56:40.5062 Info Attaching target richTextBox_wrapped to textbox BaseForm.rtbStatus
2023-07-28 11:56:42.6583 Info Registered target NLog.Targets.FileTarget(Name=OPC-TagLog)
2023-07-28 11:56:42.6583 Info Validating config: TargetNames=file, trace, richTextBox, OPC-TagLog, ConfigItems=38, FilePath=.\MyApp\bin\Debug\net6.0-windows\NLog.config
2023-07-28 11:56:42.6583 Info Closing old configuration.
2023-07-28 11:56:42.7235 Info Validating config: TargetNames=file, trace, richTextBox, OPC-TagLog, ConfigItems=38, FilePath=.\MyApp\bin\Debug\net6.0-windows\NLog.config
2023-07-28 11:56:42.7235 Info Attaching target richTextBox_wrapped to textbox BaseForm.rtbStatus
2023-07-28 11:56:42.8612 Info Registered target NLog.Targets.FileTarget(Name=AS400-AS400 Resolution Connection Data Source0)
2023-07-28 11:56:42.8612 Info Validating config: Targets=5, ConfigItems=46, FilePath=.\MyApp\bin\Debug\net6.0-windows\NLog.config
2023-07-28 11:56:42.8612 Info Closing old configuration.
2023-07-28 11:56:42.8889 Info Validating config: Targets=5, ConfigItems=46, FilePath=.\MyApp\bin\Debug\net6.0-windows\NLog.config
2023-07-28 11:56:42.8889 Info Attaching target richTextBox_wrapped to textbox BaseForm.rtbStatus

型
我们认为在创建新目标后重新初始化RichTextBoxTarget时，另一个线程尝试写入NLog时出现了问题。
我们尝试在创建新的FileTarget时使用LogManager.SuspendLogging，但仍然得到相同的错误。我们还删除了LogManager.ReconfigExistingLoggers行，但这也产生了相同的错误。
这似乎是特定于.NET 6的，因为在升级之前我们没有这个问题。