Custom config section: Could not load file or assembly

Question

I'm having a very hard time trying to access a custom configuration section in my config file.

The config file is being read from a .dll that is loaded as a plug-in. I created the Configuration and necessary code using the Configuration Section Designer VS addin.

The namespace is 'ImportConfiguration'. The ConfigurationSection class is 'ImportWorkflows'. The assembly is ImportEPDMAddin.

The xml:

  <configSections>
    <section name="importWorkflows" type="ImportConfiguration.ImportWorkflows, ImportEPDMAddin"/>
  </configSections>

Whenever I try to read in the config, I get the error:

An error occurred creating the configuration section handler for importWorkflows: Could not load file or assembly 'ImportEPDMAddin.dll' or one of its dependencies. The system cannot find the file specified.

The dll will not reside in the same directory as the executable as the software that loads the plugin places the dll and it's dependencies in it's own directory. (I can't control that.)

I edited the code for the singleton instance to the following:

string path = System.Reflection.Assembly.GetCallingAssembly().CodeBase;
path = path.Replace("file:///", "");
System.Configuration.Configuration configuration = System.Configuration.ConfigurationManager.OpenExeConfiguration(path);
return configuration.GetSection(ImportWorkflowsSectionName) as ImportConfiguration.ImportWorkflows;

I have also tried using a simple NameValueFileSectionHandler as well, but I get an exception saying that it can't load file or assembly 'System'.

I have read numerous blog posts and articles and it sounds like it is possible to read a config file in for a dll, but I just can't get it to work. Any ideas? Thanks.

Answer 1

Have you made sure that DLL is loaded first? Perhaps with Assembly.LoadFile("PATH")?

If you can't get the classes in System.Configuration to work properly, you can always fall back on using XmlDocument to manually parse the configuration file. Use XPaths to make getting the data easier. For example (assuming your path variable above):

var document = new XmlDocument();
document.Load(path);
var node = document.SelectSingleNode("configuration/importWorkflows/add[@name='KEY']");
// Do whatever with node

Answer 2

Could you verify that the probing paths are setup correctly in your Host application's config file? It is possible that a needed reference is not being loaded in your current application domain.

Assembly Binding ->Probing

Answer 3

Unfortunately, you will need to either have the ImportEPDMAddin assembly residing in the same folder as your executable, residing the .Net framework folder related to the .Net framework you are using (i.e., C:\Windows\Microsoft.NET\Framework\v2.0.50727, or registered in the Global Assembly Cache.

The only other option is, if you know the path to the assembly that contains the configuration handler's defining class, you can load it without a reference with something like this:

//Class global
private Assembly configurationDefiningAssembly;

protected TConfig GetCustomConfig<TConfig>(string configDefiningAssemblyPath, 
    string configFilePath, string sectionName) where TConfig : ConfigurationSection
{
    AppDomain.CurrentDomain.AssemblyResolve += new 
        ResolveEventHandler(ConfigResolveEventHandler);
    configurationDefiningAssembly = Assembly.LoadFrom(configDefiningAssemblyPath);
    var exeFileMap = new ExeConfigurationFileMap();
    exeFileMap.ExeConfigFilename = configFilePath;
    var customConfig = ConfigurationManager.OpenMappedExeConfiguration(exeFileMap, 
        ConfigurationUserLevel.None);
    var returnConfig = customConfig.GetSection(sectionName) as TConfig;
    AppDomain.CurrentDomain.AssemblyResolve -= ConfigResolveEventHandler;
    return returnConfig;
}

protected Assembly ConfigResolveEventHandler(object sender, ResolveEventArgs args)
{
    return configurationDefiningAssembly;
}

Make sure you handle the AssemblyResolve event, as this will throw an exception without it.