C#/ASP.NET MVC 4 Instantiate Object Derived From Interface In Factory Method

Question

Currently have a Factory class that features a GetSelector function, which returns a concrete implementation of ISelector . I have several different classes that implement ISelector and based on a setting I would like to receive the appropriate ISelector back.

public interface ISelector
{
    string GetValue(string Params);
}

public class XmlSelector : ISelector
{
    public string GetValue(string Params)
    {
        // open XML file and get value
    }
}

public static class SelectorFactory
{
    public static ISelector GetSelector()
    {
        return new XmlSelector(); // Needs changing to look at settings
    }
}

My question is what is the best way to store the setting? I am aware of using AppSettings etc. but I'm not sure whether I want to have to store strings in the web.config and perform a switch on it - just seems to be really tightly coupled in that if a new implementation of ISelector is made, then the Factory would need to be changed. Is there any way of perhaps storing an assembly name and instantiating based on that?

Thanks,

Chris

Answer 1

It is hard to say, because I don't know the architecture of your particular project, but at a first glance what I would do is if the objects associated with ISelector can be decoupled from your web application, I would put these objects in a class library along with the factory. Your factory will need to be changed if you implement a new ISelector, but if you can decouple the whole ISelector family from your actual web application the depth of the refactoring you will have to do will be minimal compared to a monolithic architecture.

Personally, I tend to avoid AppSettings, web.config settings and the like for mission-critical design questions. Using the web.config as an example, I have seen applications where architectural data is stored for ease of configurability. The problem is that after compilation your web.config can be changed (that is the purpose of it after all) and if the implementation of your classes depends on very specific values being chosen, you are running a risk of a crash when someone inadvertently modifies the wrong value.

Like I said all this depends entirely on your application architecture, but my reflex would be to split out the components that could be subject to future modification into a class library. Loose coupling is your friend ;).

Answer 2

我认为不是在AppSettings中这样做，而是一种更好的方法是创建一个单独的XML文件，该文件仅保存映射，您可以从该文件中迭代映射并在GetSelector()返回正确的实例。