When developing all kind of projects a good strategy for logging can save you a lot of time and frustration. Personally I am very found of using Apache log4net and this post will describe the most important features in log4net and how to implement and use this in a .Net Compact Framework project.

log4net can be configured with different appenders that logs to different sources (file, output window, smtp, server ++). You can also configure what kind of log levels will be written to the different appenders (info, debug, warn, error and fatal).

Most of the time I use two different appenders: I use the DebugAppender to log to my output window in Visual Studio, I like to set this appender to log all levels. I also like to use a LogFileAppender to log to a file on the device, I usually set this appender to only log error and fatal.

You can read documentation and download Apache log4net at http://logging.apache.org/log4net/index.html

I will show you a simple example on how to use log4net in a .Net Compact Framework project:

First you create a new Smart Device project and chose Device application. I am using Visual Studio 2008, Windows Mobile 6 professional SDK as target platform and .Net Compact Framework 3.5

The first thing you need to do after creating the project is to add the log4net.dll as a reference (log4net.dll can be downloaded from the link above).

Then you need to add a xml configuration file for log4net in your project, I added a file called Config.xml in my project and set the property to content/copy always. In this configuration file you add and setup all the different appenders and what level they will log on. You can also defined a layout pattern for the log text.

Below you can see my very simple Config.xml file containing a LogFileAppender and a DebugAppender and they are both set to log all levels.

<?xml version="1.0" encoding="utf-8" ?>
<!-- .NET application configuration file -->
<configuration>
	<!-- This section contains the log4net configuration settings -->
	<log4net>
		<!-- Define some output appenders -->
		<appender name="LogFileAppender" type="log4net.Appender.FileAppender" >
			<file value="log-file.txt" />
			<appendToFile value="true" />
			<layout type="log4net.Layout.PatternLayout">
				 <conversionPattern value="%date [%-5level] - %message%newline" />
			</layout>
		</appender>
    <appender name="DebugAppender" type="log4net.Appender.DebugAppender">
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="%date [%-5level] - %message%newline" />
      </layout>
    </appender>
    <!-- Setup the root category, add the appenders
           and set the default level -->
		<root>
			<level value="ALL" />
      <appender-ref ref="DebugAppender" />
      <appender-ref ref="LogFileAppender" />
		</root>
	</log4net>
</configuration>

In your Main method (by default found in Program.cs) you need to configure log4net based on the Config.xml file

//Load Config.xml to setup log4net
string path = System.IO.Path.GetDirectoryName(
    System.Reflection.Assembly.GetExecutingAssembly()
   .GetModules()[0].FullyQualifiedName)
   + "\\Config.xml";
if (System.IO.File.Exists(path))
  {
      XmlConfigurator.Configure(new System.IO.FileInfo(path));
  }

log4net are now ready to be used in all classes throughout your project. For each class you want to use log4net create a static logger object in top of your class. Remember that the typeof () must be set to the class you create this logger in.

// Create a logger for use in this class
private static readonly log4net.ILog Log = log4net.LogManager.GetLogger(typeof (Program));
[csharp]
I often use the logger to log exceptions but I also use it for information and debug.
[csharp]
//Information logging
Log.Info("Application startup");
//Debug logging
Log.Debug("Debug statement");
//Warning logging
Log.Warn("Could not find all images");

//Exception logging
catch(Exception ex)
  {
     Log.Error("Custom exception message", ex);
  }

The log file on the device can be found under program files\yourProjectName\log-file.txt. This text file on the device is a very good place to for example log your global exception handling.