Entlib and interop: does it work and where does the config file go?
I am trying to use EntLib 3.1 inside .net code for a dll registered for COM interop. Where can I put the config file?
Alternatively, is there a way to tell inside the dll code where it should get the entlib config from? Since my dll will be called from COM, I don't always know what exe will be calling it.
I created a simple application that uses Entlib logging, with two classes, "CallingApp" and "MyComThing". When I call the MyComThing method from CallingApp, it is registered with configuration in the CallingApp config file. When I call the MyComThing method from a vbs script, that is, via COM, I get the error "The configuration section for logging could not be found in the config source." My COMThing.dll.config file is located in the same folder as the registered COMThing.dll, i.e. in the bin \ debug \ folder.
thank!
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The answer is that the enterprise library uses the exe config file by default. If you are creating dlls including COM then for good reason you may not want to depend on the calling executable. One solution to this (and maybe others) is to create Enterprise Library objects yourself rather than using the default ones, and tell them where to get the configuration. It's not as scary as it sounds and doesn't require recompiling entlib or anything like that.
Instead of just using Logger.Write (), I did the following: a) Create a log record using the dll config file:
string dllConfigFilename = Assembly.GetExecutingAssembly().Location + ".config";
FileConfigurationSource exceptionsSource = new FileConfigurationSource(dllConfigFilename);
LogWriterFactory writerFactory = new LogWriterFactory(exceptionsSource);
logWriter = writerFactory.Create();
b) Then use this log entry in your code:
LogEntry log = new LogEntry();
log.Message = message;
log.Categories = new string[] { "General" };
logWriter.Write(log);
Here's the complete code for the sample object I created. References were Microsoft.Practices.EnterpriseLibrary.Common, Microsoft.Practices.EnterpriseLibrary.Logging, Microsoft.Practices.ObjectBuilder, System, System.Data, System.Windows.Forms, System.Xml:
using System;
using System.Collections.Generic;
using System.Text;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using System.Reflection;
using System.IO;
using Microsoft.Practices.EnterpriseLibrary.Logging;
using Microsoft.Practices.EnterpriseLibrary.Common.Configuration;
namespace COMThing
{
[ComVisible(true)]
public class MyComThing : MyComInterface
{
LogWriter logWriter;
public MyComThing()
{
string dllConfigFilename = Assembly.GetExecutingAssembly().Location + ".config";
FileConfigurationSource exceptionsSource = new FileConfigurationSource(dllConfigFilename);
LogWriterFactory writerFactory = new LogWriterFactory(exceptionsSource);
logWriter = writerFactory.Create();
}
public bool ProcessMessage(string message)
{
LogEntry log = new LogEntry();
log.Message = message;
log.Categories = new string[] { "General" };
logWriter.Write(log);
MessageBox.Show(message);
return true;
}
}
}
The project includes a COMThing.dll.config file which I set 'Copy to Output Directory' to 'Copy always'. This is a trivial configuration that writes log information to the application event log. Configuration file content:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<configSections>
<section name="loggingConfiguration" type="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.LoggingSettings, Microsoft.Practices.EnterpriseLibrary.Logging, Version=3.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
<section name="dataConfiguration" type="Microsoft.Practices.EnterpriseLibrary.Data.Configuration.DatabaseSettings, Microsoft.Practices.EnterpriseLibrary.Data, Version=3.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
</configSections>
<loggingConfiguration name="Logging Application Block" tracingEnabled="true"
defaultCategory="General" logWarningsWhenNoCategoriesMatch="true">
<listeners>
<add source="COMThing Logger" formatter="Text Formatter" log="Application"
machineName="" listenerDataType="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.FormattedEventLogTraceListenerData, Microsoft.Practices.EnterpriseLibrary.Logging, Version=3.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
traceOutputOptions="None" type="Microsoft.Practices.EnterpriseLibrary.Logging.TraceListeners.FormattedEventLogTraceListener, Microsoft.Practices.EnterpriseLibrary.Logging, Version=3.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
name="Formatted EventLog TraceListener" />
</listeners>
<formatters>
<add template="Timestamp: {timestamp}
Message: {message}
Category: {category}
Priority: {priority}
EventId: {eventid}
Severity: {severity}
Title:{title}
Machine: {machine}
Application Domain: {appDomain}
Process Id: {processId}
Process Name: {processName}
Win32 Thread Id: {win32ThreadId}
Thread Name: {threadName}
Extended Properties: {dictionary({key} - {value}
)}"
type="Microsoft.Practices.EnterpriseLibrary.Logging.Formatters.TextFormatter, Microsoft.Practices.EnterpriseLibrary.Logging, Version=3.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
name="Text Formatter" />
</formatters>
<categorySources>
<add switchValue="All" name="General">
<listeners>
<add name="Formatted EventLog TraceListener" />
</listeners>
</add>
</categorySources>
<specialSources>
<allEvents switchValue="All" name="All Events">
<listeners>
<add name="Formatted EventLog TraceListener" />
</listeners>
</allEvents>
<notProcessed switchValue="All" name="Unprocessed Category" />
<errors switchValue="All" name="Logging Errors & Warnings">
<listeners>
<add name="Formatted EventLog TraceListener" />
</listeners>
</errors>
</specialSources>
</loggingConfiguration>
</configuration>
In the project properties under Build, select the Register COM Interop checkbox. Create a project, then create the following .vbs file:
Set obj = CreateObject("COMThing.MyComThing")
obj.ProcessMessage("called from com by vbs")
If you double click this vbs file, it should display a message box with the text 'called from com by vbs' and write an entry to its application event log. This demonstrates that although the execution process is C: \ WINDOWS \ System32 \ WScript.exe (or similar), it gets the configuration from your dll config file.
I based this on the information here under "Using Multiple Configuration Sources".
Note that the Logger class includes many good helper methods with different arguments. Since we are using the LogWriter class, we are not getting this magic. Personally, I will create another class in my library to do the same job based on Logger.
This article demonstrates the same principle as for database application blocks and exceptions. Presumably the same model can be applied to most / all of them.
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