Conditional type resolving in C# with Unity or MEF

Question

I'm working on an application architecture and i'm facing a BIG question. The app is quite simple, it receives a file, the app apply a syntaxe validation,a parsing,... and other stuff. We can have diffrent type of files (eg : File1.xx, File2.yy), each File type has a specefic implementation of Syntax validation and parsing. The main constraint is to have a generic and easily extensible application ( can extend the type of managed files).

That's why i have imagined something like :

An Interface "IFileProcessor" in which i have 2 methods (or more) -bool IsSytaxValid(File f) -String Parse(...)

In the app i shoud have something like :

**// For a current File F1
IFileProcessor fileProcessor;
if (fileProcessor.IsSyntaxtValid(){
fileProcessor.Parse();
}else
 {
  bla bla bla
 }**

I want to have a plugin for File1.xx an another from File2.yy(2 dll in which i implement IFileProcessor interface). The processing implemention, according the current file type, is dynamically loaded.

I have a basic knowledges about Unity and MEF, i know it's my issue is managed by these kind of framworks.

The Question is, which solution is the best to resolve my issue, and how i can do it ?

Thanks in advance for your Help.

Answer 1

If you use the file extension to discern between the file types, you can create named registrations for IFileProcessor based on the file extension. When resolving the IFileProcessor , you use the extension of the file that you want to parse and by that acquire the correct instance.

You can create a named registration like this programmatically:

IUnityContainer container = new UnityContainer();
container.RegisterType<IFileProcessor, TxtFileProcessor>(".txt");
container.RegisterType<IFileProcessor, CsvFileProcessor>(".csv");

As you want to use a Plugin model, you can also create the registrations by configuring the Unity container accordingly, eg:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <configSections>
        <section name="unity" type="Microsoft.Practices.Unity.Configuration.UnityConfigurationSection, Microsoft.Practices.Unity.Configuration" />
    </configSections>
    <unity>
        <containers>
            <container>
                <types>
                    <type name=".txt"
                          type="MyNamespace.IFileProcessor, MyAssembly"
                          mapTo="MyPluginNamespace.TxtFileProcessor, MyPluginAssembly"/>
                </types>
            </container>
        </containers>
   </unity>

And resolve it like this:

var fileExt = System.IO.Path.GetExtension(filePath);
var fileProc = container.Resolve<IFileProcessor>(fileExt.ToLower());

Please note that the GetExtension method returns the leading "." of the extension, so you either have to remove it or configure your mapping names with a leading ".".