Avoiding Service Locator with AutoFac 2

问题

I'm building an application which uses AutoFac 2 for DI. I've been reading that using a static IoCHelper (Service Locator) should be avoided.

IoCHelper.cs

public static class IoCHelper
{
    private static AutofacDependencyResolver _resolver;

    public static void InitializeWith(AutofacDependencyResolver resolver)
    {
        _resolver = resolver;
    }

    public static T Resolve<T>()
    {
        return _resolver.Resolve<T>();
    }
}

From answers to a previous question, I found a way to help reduce the need for using my IoCHelper in my UnitOfWork through the use of Auto-generated Factories. Continuing down this path, I'm curious if I can completely eliminate my IoCHelper.

Here is the scenario:

I have a static Settings class that serves as a wrapper around my configuration implementation. Since the Settings class is a dependency to a majority of my other classes, the wrapper keeps me from having to inject the settings class all over my application.

Settings.cs

public static class Settings
{
    public static IAppSettings AppSettings
    {
        get
        {
            return IoCHelper.Resolve<IAppSettings>();
        }
    }
}

public interface IAppSettings
{
    string Setting1 { get; }
    string Setting2 { get; }
}

public class AppSettings : IAppSettings
{
    public string Setting1
    {
        get
        {
            return GetSettings().AppSettings["setting1"];
        }
    }

    public string Setting2
    {
        get
        {
            return GetSettings().AppSettings["setting2"];
        }
    }

    protected static IConfigurationSettings GetSettings()
    {
        return IoCHelper.Resolve<IConfigurationSettings>();
    }
}

Is there a way to handle this without using a service locator and without having to resort to injecting AppSettings into each and every class? Listed below are the 3 areas in which I keep leaning on ServiceLocator instead of constructor injection:

AppSettings
Logging
Caching

回答1:

I would rather inject IAppSettings into every class that needs it just to keep them clean from the hidden dependency on Settings. Question is, do you really need to sprinkle that dependency into each and every class?

If you really want to go with a static Settings class I would at least try to make it test-friendly/fakeable. Consider this:

public static class Settings
{
    public static Func<IAppSettings> AppSettings { get; set; }
}

And where you build your container:

var builder = new ContainerBuilder();
...
var container = builder.Build();

Settings.AppSettings = () => container.Resolve<IAppSettings>();

This would allow to swap out with fakes during test:

Settings.AppSettings = () => new Mock<IAppSettings>().Object;

Now the AppSettings class (which I assume there is only one of) you could do with regular constructor injection. I assume also that you really want to do a resolve on each call to your settings properties, thus injecting a factory delegate that retrieves an instance when needed. If this is not needed you should of course inject the IConfigurationSettings service directly.

public class AppSettings : IAppSettings
{
    private readonly Func<IConfigurationSettings> _configurationSettings;

    public AppSettings(Func<IConfigurationSettings> configurationSettings)
    {
        _configurationSettings = configurationSettings;
    }

    public string Setting1
    {
        get
        {
            return _configurationSettings().AppSettings["setting1"];
        }
    }

    public string Setting2
    {
        get
        {
            return _configurationSettings().AppSettings["setting2"];
        }
    }
}

来源：https://stackoverflow.com/questions/2737583/avoiding-service-locator-with-autofac-2

标签

ioc-container

autofac