Added FileLevel and FileName settings.

Author: Sergey-Vlasov

Source/ExcelDna.Integration/Logging.cs

@@ -143,6 +143,16 @@ public static void Initialize()
                         IntegrationTraceSource.Listeners.Add(new LogDisplayTraceListener("LogDisplay", settings.LogDisplayLevel));
                     }
 
+                    if (!string.IsNullOrWhiteSpace(settings.FileName))
+                    {
+                        Trace.AutoFlush = true;
+
+                        TextWriterTraceListener textWriterTraceListener = new TextWriterTraceListener(settings.FileName, "FileWriter");
+                        if (settings.FileLevel.HasValue)
+                            textWriterTraceListener.Filter = new DiagnosticsFilter(settings.FileLevel.Value);
+                        IntegrationTraceSource.Listeners.Add(textWriterTraceListener);
+                    }
+
                     AppDomain currentDomain = AppDomain.CurrentDomain;
                     //currentDomain.UnhandledException += UnhandledExceptionHandler;
                     currentDomain.DomainUnload += AppDomainUnloadEvent;

Source/ExcelDna.Integration/LoggingSettings.cs

@@ -9,6 +9,8 @@ internal class LoggingSettings
         public SourceLevels SourceLevel { get; }
         public TraceEventType? LogDisplayLevel { get; }
         public TraceEventType? DebuggerLevel { get; }
+        public TraceEventType? FileLevel { get; }
+        public string FileName { get; }
 
         public LoggingSettings()
         {
@@ -19,6 +21,11 @@ public LoggingSettings()
 
             if (Enum.TryParse(GetCustomSetting("DEBUGGER_LEVEL", "DebuggerLevel"), out TraceEventType debuggerLevelResult))
                 DebuggerLevel = debuggerLevelResult;
+
+            if (Enum.TryParse(GetCustomSetting("FILE_LEVEL", "FileLevel"), out TraceEventType fileLevelResult))
+                FileLevel = fileLevelResult;
+
+            FileName = GetCustomSetting("FILE_NAME", "FileName");
         }
 
         private static string GetCustomSetting(string environmentName, string registryName)