Skip to main content

Configuring NLog Logging

This is a guide to setting up logging from within your Excel-DNA add-in, using the NLog library. I used Visual Studio 2012 and C# to put together the example, but nothing here should be specific to the particular versions or language used.

1. Create a new C# Class Library

Start Visual Studio, select New Project... and make a new C# Class Library project. I targeted the .NET Framework 4.5 since that is the default, but .NET Framework 4 should also work fine. I called my library NLogTest.

2. Install the Excel-DNA NuGet package

Open the NuGet Package Manager Console (Tools -> Library Package Manager -> Package Manager Console) and enter "Install-Package Excel-DNA". This will install the Excel-DNA package and display the Readme.txt file when complete.

3. Test basic add-in functionality

From inside the displayed Readme.txt file, copy the C# sample snippet into the file Class1.cs:

using ExcelDna.Integration;

public static class MyFunctions
[ExcelFunction(Description = "My first .NET function")](ExcelFunction(Description-=-_My-first-.NET-function_))
public static string HelloDna(string name)
return "Hello " + name;

(You can also rename the Class1.cs file if you want to.)

Notice that the NuGet package has set up the following aspects:

  • Added a NLogTest-AddIn.dna file.
  • Added a post-build step that will copy the ExcelDna.xll to the output directory as NLogTest-AddIn.xll.
  • Added a post-build step that will run ExcelDnaPack to pack the add-in to produce NLogTest-AddIn-packed.xll in the output directory.
  • Configured debugging to start Excel and load add-in.

Now press F5 to build and start debugging. This should load Excel and the add-in, and make the HelloDna function available. Try it in a cell as "=HelloDna("World!")

Exit Excel to stop debugging.

Install the NLog library

Back in the Package Manager Console, install the NLog package: "Install-Package NLog". This should add a reference to the NLog library.

Add a configuration file

The name of the actual Excel add-in is NLogTest-AddIn.xll (this is the name set up by the Excel-DNA NuGet package). A configuration file for this add-in will be called NLogTest-AddIn.xll.config. We add such a file to the project: Right-click on the Project in the Solution Explorer, and select Add -> New Item.... Select Application Configuration File, and set the filename to NLogTest-AddIn.xll.config. This name must match the .xll name exactly (plus an extra .config extension). Right-click on the new file in the Solution Explorer, pick Properties, and set the file to: Copy to Output Directory: Copy if newer. This will ensure the file is copied to the output when changed.

Add the NLog configuration entries

The configuration file might look like this:

<?xml version="1.0" encoding="utf-8" ?>
<section name="nlog" type="NLog.Config.ConfigSectionHandler, NLog"/>
<nlog xmlns="" xmlns:xsi="">
<target name="logfile" xsi:type="File" fileName="${basedir}/LogFile.txt"/>
<logger name="*" minLevel="Info" writeTo="logfile"/>

Add some logging to your function

using ExcelDna.Integration;
using NLog;

public static class MyFunctions
private static readonly Logger logger = LogManager.GetCurrentClassLogger();

[ExcelFunction(Description = "My first .NET function")](ExcelFunction(Description-=-_My-first-.NET-function_))
public static string HelloDna(string name)
logger.Info("HelloDna function called: {0}", name);
return "Hello " + name;

Press F5 to build and start Excel, and enter the function into a cell: =HelloDna("World!") (If there is an error in the configuration or in using NLog, the function will return #VALUE!)

Check the bin\Debug output directory of the project - the LogFile.txt should be created, with the logged function call: 2013-11-14 16:23:15.0465|INFO|MyFunctions|HelloDna function called: World!

Add NLog to the packed .xll

Excel-DNA can pack the dependencies of an .xll into a single file add-in. The NLogTest-AddIn.xll.config file is automatically added by the ExcelDnaPack utility, but we also want to add the NLog library itself. To do this, update the NLogTest-AddIn.dna file by adding a <Reference> entry for NLog as follows:

<DnaLibrary Name="NLogTest Add-In" RuntimeVersion="v4.0">
<Reference Path="NLog.dll" Pack="true" />
<ExternalLibrary Path="NLogTest.dll" LoadFromBytes="true" Pack="true" />

Then rebuild the project again.

Check the final packed add-in

The resulting packed add-in, called NLogTest-AddIn-packed.xll is a single-file add-in that includes the configuration file and NLog library. Copy this file from the bin\Debug output directory into a new directory (as the only file in the directory) and double-click to open in Excel. Then call the HelloDna function again and check that the log file is created.

The resulting packed add-in can be renamed and distributed with no other dependencies required.