How to use Action Filters with Dependency Injection in ASP.NET CORE?

Question

I use constructor-based dependency injection everywhere in my ASP.NET CORE application and I also need to resolve dependencies in my action filters:

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Answer 1

If you want to avoid the Service Locator pattern you can use DI by constructor injection with a TypeFilter.

In your controller use

[TypeFilter(typeof(MyActionFilterAttribute), Arguments = new object[] {10})]
public IActionResult() NiceAction
{
   ...
}

And your ActionFilterAttribute does not need to access a service provider instance anymore.

public class MyActionFilterAttribute : ActionFilterAttribute
{
    public int Limit { get; set; } // some custom parameters passed from Action
    private ICustomService CustomService { get; } // this must be resolved

    public MyActionFilterAttribute(ICustomService service, int limit)
    {
        CustomService = service;
        Limit = limit;
    }

    public override async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
    {
        await next();
    }
}

For me the annotation [TypeFilter(typeof(MyActionFilterAttribute), Arguments = new object[] {10})]seems to be awkward. In order to get a more readable annotation like [MyActionFilter(Limit = 10)]your filter has to inherit from TypeFilterAttribute. My answer of How do I add a parameter to an action filter in asp.net? shows an example for this approach.

Answer 2

You can use ServiceFilters to instantiate the ActionFilters you need in the controller.

In the controller:

[ServiceFilter(typeof(TrackingAttribute), Order = 2)]

You need to register TrackingAttribute in the dependency container so the ServiceFilter can resolve it.

Read more about this at https://www.strathweb.com/2015/06/action-filters-service-filters-type-filters-asp-net-5-mvc-6/

Answer 3

You can use Service Locator:

public void OnActionExecuting(ActionExecutingContext actionContext)
{
     var service = actionContext.HttpContext.RequestServices.GetService<IService>();
}

Note that the generic method GetService<> is an extension method and lives in namespace Microsoft.Extensions.DependencyInjection.

If you want to use constructor injection use TypeFilter. See How do I add a parameter to an action filter in asp.net?