せっかく、asp.net core なんだから、アトリビュートもDIしたいよね。

ASP.net Core、使っていると、もれなくDI「dependency injection」がついてくるよね。
ちゃんと使っている？

でも、Contorllerのアクションでよく使う、バリデーションのActionFilterAttributeってそのままでは、DIできないですよね！

こんな感じで実装して

```C#:TestFilterAttribute.cs
using System.Linq;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.AspNetCore.Mvc.ModelBinding;

namespace Attribute.Attribute
{
    public class TestFilterAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext actionContext)
        {
            if (!actionContext.ActionArguments.All(x => x.Key != "id" || CheckValue(x.Value as int?)))
            {
                actionContext.Result = new BadRequestObjectResult(new ModelStateDictionary());
            }
        }


        private bool CheckValue(int? value)
        {
            if (value == null) return false;
            if (value < 1) return false;
            return true;
        }
    }

}
```
こんな感じで呼び出す

```C#:TestController.cs
using Attribute.Attribute;
using Attribute.Model;
using Microsoft.AspNetCore.Mvc;

namespace Attribute
{
    public class TestController : Controller
    {
        public TestController()
        {

        }
        // GET: HomeController
        public ActionResult Index()
        {
            return View(new TestViewModel());
        }

        // GET: HomeController/Details/5
        [TestFilter]
        public ActionResult Details(int id)
        {
            return View(new TestViewModel(){Id = id});
        }
    }
}

```
[TestFilter]という形で呼び出すんだからDIできないんだけれど。

さすがの、.net
IFilterFactory というインターフェースがありました

こいつを継承すると

まず、TestFilterAttributeにインターフェースを追加

```C#:TestFilterAttribute

using System.Linq;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.AspNetCore.Mvc.ModelBinding;

namespace Attribute.Attribute
{
    public class TestFilterAttribute : ActionFilterAttribute, ITestFilterAttribute 
    {
        public override void OnActionExecuting(ActionExecutingContext actionContext)
        {
            if (!actionContext.ActionArguments.All(x => x.Key != "id" || CheckValue(x.Value as int?)))
            {
                actionContext.Result = new BadRequestObjectResult(new ModelStateDictionary());
            }
        }


        private bool CheckValue(int? value)
        {
            if (value == null) return false;
            if (value < 1) return false;
            return true;
        }
    }

}
```

```c#:ITestFilterAttribute.cs
using Microsoft.AspNetCore.Mvc.Filters;

namespace Attribute.Attribute
{
    public interface ITestFilterAttribute : IActionFilter
    {
    }
}
```

Startupに追加
            services.AddScoped<ITestFilterAttribute, TestFilterAttribute>();

```C#:Startup.cs
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Attribute.Attribute;

namespace Attribute
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddRazorPages(); 
            services.AddScoped<ITestFilterAttribute, TestFilterAttribute>();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Error");
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(name: "default", pattern: "{controller=Permission}/{action=Index}/{id?}");
                endpoints.MapRazorPages();
            });
        }
    }
}
```

Factry、を追加して、そこから ITestFilterAttribute　を呼び出す

```C#:TestFilterFactoryAttribute.cs
using System;
using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.Extensions.DependencyInjection;

namespace Attribute.Attribute
{
    public class TestFilterFactoryAttribute : System.Attribute, IFilterFactory
    {
        public bool IsReusable => false;

        public IFilterMetadata CreateInstance(IServiceProvider serviceProvider)
        {
            // DIのServiceProviderからITestFilterAttributeを取り出す
            ITestFilterAttribute filter = serviceProvider.GetService<ITestFilterAttribute>();

            return filter;
        }
    }
}

```

で、Factryの方を呼び出すように、Controllerを変更

```C#:TestController.cs
using Attribute.Attribute;
using Attribute.Model;
using Microsoft.AspNetCore.Mvc;

namespace Attribute
{
    public class TestController : Controller
    {
        public TestController()
        {

        }
        // GET: HomeController
        public ActionResult Index()
        {
            return View(new TestViewModel());
        }

        // GET: HomeController/Details/5
        [TestFilterFactory]
        public ActionResult Details(int id)
        {
            return View(new TestViewModel(){Id = id});
        }
    }
}

```

という感じです

まあ、サービスプロバイダーとしての実装になっちゃうんですけど