[c#] app.config for a class library

I cannot see a app.config file generated for a class library by the VS2008 wizard. In my research I found that in an application only one app.config exists.

Is it a bad thing to add an app.config manually to a class library or are there any other methods which will serve the purpose of an app.config in class library?

I need to store log4net config information inside the app.config file.

I would recommend using Properties.Settings to store values like ConnectionStrings and so on inside of the class library. This is where all the connection strings are stores in by suggestion from visual studio when you try to add a table adapter for example. enter image description here

And then they will be accessible by using this code every where in the clas library

var cs=  Properties.Settings.Default.[<name of defined setting>];

I don't know why this answer hasn't already been given:

Different callers of the same library will, in general, use different configurations. This implies that the configuration must reside in the executable application, and not in the class library.

You may create an app.config within the class library project. It will contain default configurations for items you create within the library. For instance, it will contain connection strings if you create an Entity Framework model within the class library.

However, these settings will not be used by the executable application calling the library. Instead, these settings may be copied from the library.dll.config file into the app.config or web.config of the caller, so that they may be changed to be specific to the caller, and to the environment into which the caller is deployed.

This is how it has been with .NET since Day 1.

If you want to configure your project logging using log4Net, while using a class library, There is no actual need of any config file. You can configure your log4net logger in a class and can use that class as library.

As log4net provides all the options to configure it.

Please find the code below.

public static void SetLogger(string pathName, string pattern)
        {
            Hierarchy hierarchy = (Hierarchy)LogManager.GetRepository();

            PatternLayout patternLayout = new PatternLayout();
            patternLayout.ConversionPattern = pattern;
            patternLayout.ActivateOptions();

            RollingFileAppender roller = new RollingFileAppender();
            roller.AppendToFile = false;
            roller.File = pathName;
            roller.Layout = patternLayout;
            roller.MaxSizeRollBackups = 5;
            roller.MaximumFileSize = "1GB";
            roller.RollingStyle = RollingFileAppender.RollingMode.Size;
            roller.StaticLogFileName = true;
            roller.ActivateOptions();
            hierarchy.Root.AddAppender(roller);

            MemoryAppender memory = new MemoryAppender();
            memory.ActivateOptions();
            hierarchy.Root.AddAppender(memory);

            hierarchy.Root.Level = log4net.Core.Level.Info;
            hierarchy.Configured = true;
      }

Now instead of calling XmlConfigurator.Configure(new FileInfo("app.config")) you can directly call SetLogger with desired path and pattern to set the logger in Global.asax application start function.

And use the below code to log the error.

        public static void getLog(string className, string message)
        {
            log4net.ILog iLOG = LogManager.GetLogger(className);
            iLOG.Error(message);    // Info, Fatal, Warn, Debug
        }

By using following code you need not to write a single line neither in application web.config nor inside the app.config of library.

Actually, for some rare case you could store app.config in class libraries (by adding manually) and parse it by OpenExeConfiguration.

 var fileMap =
    new ExeConfigurationFileMap {ExeConfigFilename = 
    @"C:\..somePath..\someName.config"};
 System.Configuration.Configuration config =
    ConfigurationManager.OpenMappedExeConfiguration(fileMap, 
    ConfigurationUserLevel.None);

You should really estimate the real need of this. For abstract data its not the best solution, but "Config Sections" could be very usefull!!

For example, we organised our N-Tier WCF architecture decoupled, without any metadata, simply by using Unity Container and Injection Factory based on Channel Factory T. We added externall ClassLibrary dll with just [Service Contract] Interfaces and common app.config in order to read endpoints from clientsection, and easily add/change them at one place.

Jon, a lot of opinion has been given that didn't correctly answer your question.

I will give MY OPINION and then tell you how to do exactly what you asked for.

I see no reason why an assembly couldn't have its own config file. Why is the first level of atomicy (is that a real word?) be at the application level? Why not at the solution level? It's an arbitrary, best-guess decision and as such, an OPINION. If you were to write a logging library and wanted to include a configuration file for it, that would be used globally, why couldn't you hook into the built-in settings functionality? We've all done it ... tried to provide "powerful" functionality to other developers. How? By making assumptions that inherently translated to restrictions. That's exactly what MS did with the settings framework, so you do have to "fool it" a little.

To directly answer your question, simply add the configuration file manually (xml) and name it to match your library and to include the "config" extension. Example:

MyDomain.Mylibrary.dll.Config

Next, use the ConfigurationManager to load the file and access settings:

string assemblyPath = new Uri(Assembly.GetExecutingAssembly().CodeBase).AbsolutePath;
Configuration cfg = ConfigurationManager.OpenExeConfiguration(assemblyPath);
string result = cfg.AppSettings.Settings["TEST_SETTING"].Value;

Note that this fully supports the machine.config heierarchy, even though you've explicitly chosen the app config file. In other words, if the setting isn't there, it will resolve higher. Settings will also override machine.config entries.

You do want to add App.config to your tests class library, if you're using a tracer/logger. Otherwise nothing gets logged when you run the test through a test runner such as TestDriven.Net.

For example, I use TraceSource in my programs, but running tests doesn't log anything unless I add an App.config file with the trace/log configuration to the test class library too.

Otherwise, adding App.config to a class library doesn't do anything.

In fact, the class library you are implementing, is retrieving information from app.config inside the application that is consuming it, so, the most correct way to implement configuration for class libraries at .net in VS is to prepare app.config in the application to configure everything it consumes, like libraries configuration.

I have worked a little with log4net, and I found that the one who prepared the application always had a section for log4net configuration inside main app.config.

I hope you find this information useful.

See you, and post comments about the solution you found.

EDIT:

At the next link you have an app.config with the section for log4net:

http://weblogs.asp.net/tgraham/archive/2007/03/15/a-realistic-log4net-config.aspx

Your answer for a non manual creation of an app.config is Visual Studio Project Properties/Settings tab.

When you add a setting and save, your app.config will be created automatically. At this point a bunch of code is generated in a {yourclasslibrary.Properties} namespace containing properties corresponding to your settings. The settings themselves will be placed in the app.config's applicationSettings settings.

 <configSections>
    <sectionGroup name="applicationSettings" type="System.Configuration.ApplicationSettingsGroup, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" >
        <section name="ClassLibrary.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
    </sectionGroup>
</configSections>
<applicationSettings>
    <ClassLibrary.Properties.Settings>
        <setting name="Setting1" serializeAs="String">
            <value>3</value>
        </setting>
    </BookOneGenerator.Properties.Settings>
</applicationSettings>

If you added an Application scoped setting called Setting1 = 3 then a property called Setting1 will be created. These properties are becoming at compilation part of the binary and they are decorated with a DefaultSettingValueAttribute which is set to the value you specified at development time.

     [ApplicationScopedSetting]
    [DebuggerNonUserCode]
    [DefaultSettingValue("3")]
    public string Setting1
    {
        get
        {
            return (string)this["Setting1"];
        }
    }

Thus as in your class library code you make use of these properties if a corresponding setting doesn't exist in the runtime config file, it will fallback to use the default value. That way the application won't crash for lacking a setting entry, which is very confusing first time when you don't know how these things work. Now, you're asking yourself how can specify our own new value in a deployed library and avoid the default setting value be used?

That will happen when we properly configure the executable's app.config. Two steps. 1. we make it aware that we will have a settings section for that class library and 2. with small modifications we paste the class library's config file in the executable config. (there's a method where you can keep the class library config file external and you just reference it from the executable's config.

So, you can have an app.config for a class library but it's useless if you don't integrate it properly with the parent application. See here what I wrote sometime ago: link

There is no automatic addition of app.config file when you add a class library project to your solution.

To my knowledge, there is no counter indication about doing so manualy. I think this is a common usage.

About log4Net config, you don't have to put the config into app.config, you can have a dedicated conf file in your project as well as an app.config file at the same time.

this link http://logging.apache.org/log4net/release/manual/configuration.html will give you examples about both ways (section in app.config and standalone log4net conf file)