For the purposes of this demonstration, we will be referencing non-strong-named assemblies but based on individual requirements Microsoft strong-named assemblies, or a modified set of custom assemblies can be referenced as well. Since we will also be exploring the configuration of database logging features in this chapter, we will include references to the database logging-related assemblies to the project.

The following table lists the required/optional assemblies.

Open Visual Studio 2008/2010 and create a new sample Windows Forms Application by selecting File | New | Project | Windows Forms Application, and provide the appropriate name for the solution and the desired project location. Currently, the application will have a default form and assembly references. In the Solution Explorer right-click on the References section and click on Add Reference and go to the Browse tab. Next, navigate to the Enterprise Library 5.0 installation location; the default install location is %Program Files%Microsoft Enterprise Library 5.0Bin. Now, select all the assemblies listed in the previous table. The final assembly selection will look similar to the following screenshot; note that the assemblies have been moved together for your reference.

After clicking on OK, the following screenshot displays the Solution Explorer listing all the added assemblies.

The next step is to add a configuration file to the project. Right-click on the project and navigate and click on the menu Add | New Item; this will display the Add New Item dialog. Select Application Configuration File and click on Add. This action will add a configuration file named App.config to the project. We can now add the Logging settings to the configuration file.

Before we can leverage the features of the Logging Application Block, we have to add the initial Logging Settings to the configuration file. Open the Enterprise Library configuration editor either using the shortcut available in Start | All Programs | Microsoft patterns & practices | Enterprise Library 5.0 | Enterprise Library Configuration or by just right-clicking the configuration file in the Solution Explorer window of Visual Studio IDE and clicking on Edit Enterprise Library V5 Configuration. Initially, Enterprise Library configuration editor will display two default sections: Application Settings and Database Settings.

The following screenshot displays the default settings displayed in the configuration editor:

Let us go ahead and add the Logging Settings in the configuration file. Select the menu option Blocks, which lists several application block settings to be added to the configuration. Click on the Add Logging Settings menu item to add the Logging configuration settings.

The following screenshot displays the Logging Settings section added to the configuration editor:

Notice the Logging Settings are grouped in to five headings, namely Categories, Special Categories, Logging Filters, Logging Target Listeners and Log Message Formatters. By default, the settings are configured with a category called General, Logging Target Listener as Event Log Listener and Log Message Formatter as Text Formatter. We will change the default configuration further; but for now, we are in good shape to leverage the Logging block and write our first log message.

Instead of fully qualifying the type on every instance of its usage, we can add the namespaces given below to the source code file to use the Logging block elements without fully qualifying the references. Although we will be using EnterpriseLibraryContainer to instantiate objects (so we will also add the Microsoft.Practices.EnterpriseLibrary.Common.Configuration namespace to the source file), the Unity Namespace section is listed to make you aware of the availability of the alternative approach to instantiating objects.

Core Namespaces:

Configuration Namespace (Optional): Required while using the EnterpriseLibraryContainer to instantiate objects

Unity Namespaces (Optional): Required while instantiating objects using UnityContainer

We are now ready to write our first log message. Since we are using the default configuration, the log message will use the default category General, the log entry will be written to the Windows Event Log, and the message will be formatted using the Text Formatter. The first step in writing the log message is to create an instance of LogWriter. LogWriter is an abstract class and is the primary interface in this release for creating log entries; this abstract class belongs to the Microsoft.Practices.EnterpriseLibrary.Logging namespace.

The following code snippet creates the LogWriter instance using the EnterpriseLibraryContainer class.

//Create a LogWriter instance using the EnterpriseLibraryContainer
LogWriter logWriter = EnterpriseLibraryContainer.Current.GetInstance<LogWriter>();

So now we have an instance of LogWriter (from this point on we will be using the variable logWriter to log the messages), the following code snippet calls the Write method of the LogWriter instance. The simplest overloaded Write method accepts a single parameter of type System.String representing the log message.

//Writes a new log entry to the default category
logWriter.Write("My First Log Message");

In the given code snippet, we are using the simplest overload of the Write method of the LogWriter class, this method uses the default category and the configured log destination and formatter. Execution of this code will result in creation of a log entry in the Windows Event Log. To view the result, open the Windows Event Viewer and check the log message in the Application section.

The following screenshot displays the log message written to the Windows Event Log.

We have successfully written our first log message, in hindsight we have also completed one cycle of the logging process by adding the assembly references, configuring the Logging block settings, adding the namespace, and writing the code to log the message. We will now pick each individual configuration and code elements and learn to understand them in detail.