.net – How to select a .Net application configuration file from a command line parameter

configurationconfigurationmanagernet

I would like to override the use of the standard app.config by passing a command line parameter. How do I change the default application configuration file so that when I access ConfigurationManager.AppSettings I am accessing the config file specified on the command line?

Edit:

It turns out that the correct way to load a config file that is different than the name of the EXE plus .config is to use OpenMappedExeConfiguration. E.g.

ExeConfigurationFileMap configFile = new ExeConfigurationFileMap();
configFile.ExeConfigFilename = Path.Combine(Environment.CurrentDirectory, "Shell2.exe.config");
currentConfiguration = ConfigurationManager.OpenMappedExeConfiguration(configFile,ConfigurationUserLevel.None);

This partially works. I can see all of the keys in the appSettings section but all the values are null.

Best Answer

So here is the code that actually allows me to actually access the appSettings section in a config file other than the default one.

ExeConfigurationFileMap configFile = new ExeConfigurationFileMap();
configFile.ExeConfigFilename = Path.Combine(Environment.CurrentDirectory, "Alternate.config");
Configuration config = ConfigurationManager.OpenMappedExeConfiguration(configFile,ConfigurationUserLevel.None);

AppSettingsSection section = (AppSettingsSection)config.GetSection("appSettings");
string MySetting = section.Settings["MySetting"].Value;

Related Solutions

.net – way to override ConfigurationManager.AppSettings

If you don't mind hacking around the framework and you can reasonably assume the .net framework version the application is running on (i.e. it's a web application or an intranet application) then you could try something like this:

using System;
using System.Collections.Specialized;
using System.Configuration;
using System.Configuration.Internal;
using System.Reflection;

static class ConfigOverrideTest
{
  sealed class ConfigProxy:IInternalConfigSystem
  {
    readonly IInternalConfigSystem baseconf;

    public ConfigProxy(IInternalConfigSystem baseconf)
    {
      this.baseconf = baseconf;
    }

    object appsettings;
    public object GetSection(string configKey)
    {
      if(configKey == "appSettings" && this.appsettings != null) return this.appsettings;
      object o = baseconf.GetSection(configKey);
      if(configKey == "appSettings" && o is NameValueCollection)
      {
        // create a new collection because the underlying collection is read-only
        var cfg = new NameValueCollection((NameValueCollection)o);
        // add or replace your settings
        cfg["test"] = "Hello world";
        o = this.appsettings = cfg;
      }
      return o;
    }

    public void RefreshConfig(string sectionName)
    {
      if(sectionName == "appSettings") appsettings = null;
      baseconf.RefreshConfig(sectionName);
    }

    public bool SupportsUserConfig
    {
      get { return baseconf.SupportsUserConfig; }
    }
  }

  static void Main()
  {
    // initialize the ConfigurationManager
    object o = ConfigurationManager.AppSettings;
    // hack your proxy IInternalConfigSystem into the ConfigurationManager
    FieldInfo s_configSystem = typeof(ConfigurationManager).GetField("s_configSystem", BindingFlags.Static | BindingFlags.NonPublic);
    s_configSystem.SetValue(null, new ConfigProxy((IInternalConfigSystem)s_configSystem.GetValue(null)));
    // test it
    Console.WriteLine(ConfigurationManager.AppSettings["test"] == "Hello world" ? "Success!" : "Failure!");
  }
}

C# – Is it possible to switch application configuration file at runtime for .NET application

All of the above work well if you need to replace only AppSettings section.

In case you have to run with different config files (all sections) you might want to consider launching application using a host, that creates app domain for your main application and sets different config file depending on parameters you passed in.

Here's the code that worked for me:

        AppDomainSetup setup = new AppDomainSetup();
        setup.ApplicationBase = "file://" + System.Environment.CurrentDirectory;
        setup.DisallowBindingRedirects = true;
        setup.DisallowCodeDownload = true;

        if (args.Length != 0 && args[0].Equals("-test"))
        {
            setup.ConfigurationFile = "PATH_TO_YOUR_TEST_CONFIG_FILE";
        }
        else {
            setup.ConfigurationFile = "PATH_TO_YOUR_LIVE_CONFIG_FILE";
        }

        AppDomain domain = AppDomain.CreateDomain("FRIENDLY_NAME", null, setup);
        domain.ExecuteAssembly("YourMainApp.exe");

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Related Solutions

.net – way to override ConfigurationManager.AppSettings

C# – Is it possible to switch application configuration file at runtime for .NET application

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