Develop Reference

Can I create a stateless static class in MVC back-end

I have an MVC application that contains a static class providing a boolean value to the rest of the program. My issue is that I want the boolean to reset with each call to the back-end. I want it to be "stateless", getting initialized to false for each and every back-end call. I'll then set it to true as needed. For instance, consider the following where from the Index view we load the About view and then afterwards load the Contact view ...
public static class BooleanProvider
{
public static bool theBool = false;
}
public class HomeController : Controller
{
public ActionResult Index()
{
return View();
}
public ActionResult About()
{
ViewBag.Message = "Your application description page.";
BooleanProvider.theBool = true;
return View();
}
public ActionResult Contact()
{
ViewBag.Message = "Your contact page.";
//I want BooleanProvider.theBool to be false here, since it's a different call, even though we set it to true in the About() method
return View();
}
}
When I check BooleanProvider.theBool at the commented line, it's set to true. Is there a way to "re-initialize" the boolean with every call? I'd rather not make the class instantiable and have to new it up with each controller call, but maybe there is no other way?
Thank you in advance!

You have to use Dependency injection for that.
dotnetcore solution
Scoped Lifetime is exactly what you needed.
https://learn.microsoft.com/en-us/aspnet/core/fundamentals/dependency-injection?view=aspnetcore-3.1#scoped
At your Startup.cs
public void ConfigureServices(IServiceCollection services)
{
// ...
services.AddScoped<BooleanProvider>();
// ...
}
and at your HomeController
public class HomeController : Controller
{
private readonly BooleanProvider _booleanProvider;
public HomeController (BooleanProvider booleanProvider){
_booleanProvider = booleanProvider;
// ...
}
// ...
}
not core solution
Here is a guide if you do not use dotnetcore https://learn.microsoft.com/en-us/aspnet/mvc/overview/older-versions/hands-on-labs/aspnet-mvc-4-dependency-injection
PerRequestLifetimeManager is what you needed here
Install-Package Unity.Mvc3
At Global.asax
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
RegisterGlobalFilters(GlobalFilters.Filters);
RegisterRoutes(RouteTable.Routes);
Bootstrapper.Initialise();
}
public static class Bootstrapper
{
public static void Initialise()
{
var container = BuildUnityContainer();
DependencyResolver.SetResolver(new UnityDependencyResolver(container));
}
private static IUnityContainer BuildUnityContainer()
{
var container = new UnityContainer();
Func<LifetimeManager> LM = () => { return new PerRequestLifetimeManager(); };
container.RegisterType<IBooleanProvider, BooleanProvider>(LM());
return container;
}
}
public class HomeController : Controller
{
private readonly IBooleanProvider _booleanProvider;
public HomeController (IBooleanProvider booleanProvider){
_booleanProvider = booleanProvider;
// ...
}
// ...
}

Ninject doesn't resolve dependency (parameterless constructor error)

I'm struggling with enabling Ninject's constructor injection in a Web Service application. Here's the steps I took (Visual Studio 2013):
1) Created a new project with "ASP.NET Web Application" template.
2) Selected an "Empty" application template in the second step of the project creation wizard.
3) In the third step called "Add folders and core references for" selected "Web API"
4) The project is created, now I added a controller of type "Web API 2 Controller - Empty". Added the following code:
using System.Web.Http;
namespace WebApplication1.Controllers
{
public interface IDummy
{
}
public class Dummy : IDummy
{
}
public class DefaultController : ApiController
{
public DefaultController(IDummy dummy)
{
}
[HttpGet]
[Route("")]
public string Index()
{
return "Hello World!";
}
}
}
5) Installed NuGet package: Ninject.Web.WebApi (Ninject integration for WebApi2), now I've found in other threads that to make it work with IIS I need to install Ninject.Web.Common.WebHost package. After this, the NinjectWebCommon.cs file appeared in AppStart. The only edit I did for this file was in RegisterServices method:
private static void RegisterServices(IKernel kernel)
{
kernel.Bind<IDummy>().To<Dummy>();
}
Now when I try to run the application (locally, just pressing F5 in Visual Studio) I would expect to get the Hello World string in a browser, but instead I get the infamous parameterless constructor error:
which means that the Ninject is for some reason not doing its job I guess. Unfortunately googling for solution was fruitless so far. Anyone can hint me what should I do to make this work? Thanks in advance.

I was able to get this working quite simply by using this solution. You only need to install Ninject.Web.WebApi and then add the following code.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.Http.Dependencies;
using Ninject;
using Ninject.Activation;
using Ninject.Parameters;
using Ninject.Syntax;
internal class NinjectDependencyResolver : NinjectScope, IDependencyResolver
{
private readonly IKernel kernel;
public NinjectDependencyResolver(IKernel kernel)
: base(kernel)
{
if (kernel == null)
throw new ArgumentNullException("kernel");
this.kernel = kernel;
}
public IDependencyScope BeginScope()
{
return new NinjectScope(this.kernel.BeginBlock());
}
}
internal class NinjectScope : IDependencyScope
{
protected IResolutionRoot resolutionRoot;
public NinjectScope(IResolutionRoot kernel)
{
resolutionRoot = kernel;
}
public object GetService(Type serviceType)
{
IRequest request = resolutionRoot.CreateRequest(serviceType, null, new Parameter[0], true, true);
return resolutionRoot.Resolve(request).SingleOrDefault();
}
public IEnumerable<object> GetServices(Type serviceType)
{
IRequest request = resolutionRoot.CreateRequest(serviceType, null, new Parameter[0], true, true);
return resolutionRoot.Resolve(request).ToList();
}
public void Dispose()
{
IDisposable disposable = (IDisposable)resolutionRoot;
if (disposable != null) disposable.Dispose();
resolutionRoot = null;
}
}
Usage
public static class WebApiConfig
{
public static void Register(HttpConfiguration config)
{
// Web API configuration and services
IKernel kernel = new StandardKernel();
kernel.Bind<IDummy>().To<Dummy>();
config.DependencyResolver = new NinjectDependencyResolver(kernel);
// Web API routes
config.MapHttpAttributeRoutes();
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
}
}

Failing to resolve dependencies with Unity and WebAPI

I'm receiving this odd error when trying to run my controller action in WebAPI:
An error occurred when trying to create a controller of type 'PostController'. Make sure that the controller has a parameterless public constructor.
Resolution of the dependency failed, type = "Example.Controllers.PostController", name = "(none)".
Exception occurred while: Calling constructor Example.Models.PostRepository().
Exception is: NullReferenceException - Object reference not set to an instance of an object.
Here's the problematic code:
public static class WebApiConfig
{
public static void Register(HttpConfiguration config)
{
var container = new UnityContainer();
container.RegisterType<IPostRepository, PostRepository>(new HierarchicalLifetimeManager());
config.DependencyResolver = new UnityResolver(container);
config.MapHttpAttributeRoutes();
config.Routes.MapHttpRoute(
name: "ExampleApi",
routeTemplate: "api/{controller}"
);
}
}
public class PostController : ApiController
{
IPostRepository _repository;
public PostController(IPostRepository repository)
{
_repository = repository;
}
public IEnumerable<Post> GetAllProducts()
{
return _repository.GetAll();
}
}
public class PostRepository : IPostRepository
{
private IDbConnection _connection = new SqlConnection(ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString);
public IEnumerable<Post> GetAll()
{
return _connection.Query<Post>("SELECT * FROM Posts").ToList();
}
}
public class UnityResolver : IDependencyResolver
{
protected IUnityContainer Container;
public UnityResolver(IUnityContainer container)
{
if (container == null)
{
throw new ArgumentNullException("container");
}
this.Container = container;
}
public object GetService(Type serviceType)
{
if (!Container.IsRegistered(serviceType))
{
if (serviceType.IsAbstract || serviceType.IsInterface)
{
return null;
}
}
return Container.Resolve(serviceType);
}
public IEnumerable<object> GetServices(Type serviceType)
{
try
{
return Container.ResolveAll(serviceType);
}
catch (ResolutionFailedException)
{
return new List<object>();
}
}
public IDependencyScope BeginScope()
{
var child = Container.CreateChildContainer();
return new UnityResolver(child);
}
public void Dispose()
{
Container.Dispose();
}
}
Does anyone have any idea of what might be the cause? I followed this tutorial: http://www.asp.net/web-api/overview/advanced/dependency-injection

In my experience when I see this message its normally some dependency is not able to be constructed or is missing a dependency. You have IPostRepository registered to PostRepository so that looks good. What about the SqlConnection created in PostRepository? Could you run some test code against just the repository to see if it constructs OK on its own?
Also just in browsing through your code is the check for interfaces blocking your resolution of the IPostRepository in the UnityResolver class?
if (serviceType.IsAbstract || serviceType.IsInterface)
{
return null;
}

The following link has a working project which is based on the same tutorial that you mentioned.
Not much difference to your code except the database will be targeting localdb, and on the UnityResolver there is no checks for Abstract class, which doesn't make any difference I think.
Now, you can use the project as a startup point to add your logic, and know exactly when it fails and why.
hope this helps.

Getting started with Ninject

I watched the first 2 beginner tutorials for Ninject on dimecasts.net. Now, I want to use Ninject 2.2 in ASP.NET MVC 3. I want a view with a mocked out Model. I get object reference not set to an instance of an object when calling my service;
public class HomeController : Controller
{
private readonly IMilestoneService _service;
public HomeController()
{
}
HomeController(IMilestoneService service)
{
_service = service;
}
public ActionResult Index()
{
ViewBag.Message = "Change Request System";
return View();
}
public ActionResult About()
{
return View();
}
#region Partial views
public ActionResult Milestone()
{
var result = _service.GetMileStones();//OBJECT REF ERROR
return View(result);
}
#endregion
}
//####GLOBAL.ASAX
//By using the NinjectHttpApplication, it automatically takes care of controllers, starting up mvc, etc.
//Ninject.Web.Mvc
public class MvcApplication : NinjectHttpApplication
{
public static void RegisterGlobalFilters(GlobalFilterCollection filters)
{
filters.Add(new HandleErrorAttribute());
}
public static void RegisterRoutes(RouteCollection routes)
{
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Home", action = "Index", id = UrlParameter.Optional } // Parameter defaults
);
}
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
RegisterGlobalFilters(GlobalFilters.Filters);
RegisterRoutes(RouteTable.Routes);
//StartNinject();
}
#region Inversion of Control
protected override IKernel CreateKernel()
{
return Container;
}
static IKernel _container;
public static IKernel Container
{
get
{
if (_container == null)
{
_container = new StandardKernel(new SiteModule());
}
return _container;
}
}
internal class SiteModule : NinjectModule
{
public override void Load()
{
//Set up ninject bindings here.
Bind<IMilestoneService>().To<MileStoneService>();
}
}
#endregion
}
I'm using Razor, he's the milestone partial view
#foreach (var item in Model)
{
<div>item.Name</div>
}
Finally, the Home view Index
#{
ViewBag.Title = "Home Page";
}
<h2>#ViewBag.Message</h2>
<p>
#Html.Action("Milestone");
</p>
Edit 11/20/2013
Note that Ninject has since released version 2.0. The changes are nicely outlined on their site. Of Note StandardModule is now NinjectModule and namespace Ninject.Core no longer exists. I was able to replace it with just Ninject.

There is an issue with your controller class, the constructor with the dependency is private. Your controller should look like:
public class HomeController : Controller
{
private readonly IMilestoneService _service;
public HomeController(IMilestoneService service)
{
_service = service;
}
}
Don't even include a public parameterless constructor, it isn't even valid, your class needs that dependency to function.
In fact, I also insert a null check against that dependency in the constructor just to be sure my class is valid on construction:
public class HomeController : Controller
{
private readonly IMilestoneService _service;
public HomeController(IMilestoneService service)
{
_service = service;
Enforce.NotNull(() => _service); // lambda to auto-magically get variable name for exception
}
}
There also may be an issue with your MvcApplication class.
Instead of protected void Application_Start(), there is a different function you can override, protected override void OnApplicationStarted()
This is where your calls to setup routing should go:
public class MvcApplication : NinjectHttpApplication
{
public override void Init()
{
base.Init();
Mappers.Initialize();
}
protected override Ninject.IKernel CreateKernel()
{
return Ioc.Initialize();
}
protected override void OnApplicationStarted()
{
AreaRegistration.RegisterAllAreas();
RegisterRoutes(RouteTable.Routes);
}
public static void RegisterRoutes(RouteCollection routes)
{
Routing.RegisterRoutes(routes);
//RouteDebug.RouteDebugger.RewriteRoutesForTesting(RouteTable.Routes);
}
}
Of course, if you are already calling Application_Start that's fine too, but I didn't see it in the OP.

Try this in your global.asax file:
//By using the NinjectHttpApplication, it automatically takes care of controllers, starting up ninject, etc.
//Ninject.Web.Mvc
public class MvcApplication : NinjectHttpApplication
{
//Your other stuff here. No need to call StartNinject().
#region Inversion of Control
protected override IKernel CreateKernel()
{
return Container;
}
static IKernel _container;
public static IKernel Container
{
get
{
if (_container == null)
{
_container = new StandardKernel(new SiteModule());
}
return _container;
}
}
internal class SiteModule : NinjectModule
{
public override void Load()
{
//Set up ninject bindings here.
Bind<IMilestoneService>().To<MileStoneService>();
}
}
#endregion
}

I believe if Ninject couldn't bind that interface, you'd get a binding error. This makes me think Ninject is not instantiating your controller.
Have you included Ninject.Web.Mvc?

NInject Singletons - Are they created at application or session level?

I'm using NInject in my ASP.NET MVC application and I'm not 100% sure how the singleton is working when creating my Object context.
My Question is:
Using the code below will there be one
ObjectContext per user session or will
there be one that is share for the
entire application? I want each user
to have only one context at one time,
but each user must have their own
instance.
Is InRequestScope() something I should be considering?
I also do the same thing with a WCF service and I assume the answer will be same for both.
My Global.asax:
public class MvcApplication : NinjectHttpApplication
{
public static void RegisterRoutes(RouteCollection routes)
{
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
routes.MapRoute(
"Default", // Route name
"{controller}/{action}/{id}", // URL with parameters
new { controller = "Change", action = "Index", id = UrlParameter.Optional } // Parameter defaults
);
}
protected override void OnApplicationStarted()
{
// Ninject Code
base.OnApplicationStarted();
AreaRegistration.RegisterAllAreas();
RegisterRoutes(RouteTable.Routes);
}
protected override IKernel CreateKernel()
{
var modules = new INinjectModule[] { new ContextModule() };
return new StandardKernel(modules);
}
public class ContextModule : NinjectModule
{
public override void Load()
{
Bind<ObjectContext>().To<ChangeRoutingEntities>().InSingletonScope();
Bind<IObjectContext>().To<ObjectContextAdapter>();
Bind<IUnitOfWork>().To<UnitOfWork>();
}
}
}

ISingletonScope is an application wide scope.
InRequestScope is only for the current request.
You need a session scope. See http://iridescence.no/post/Session-Scoped-Bindings-With-Ninject-2.aspx for a way to implement this type of scope.
public static class NinjectSessionScopingExtention
{
public static void InSessionScope<T>(this IBindingInSyntax<T> parent)
{
parent.InScope(SessionScopeCallback);
}
private const string _sessionKey = "Ninject Session Scope Sync Root";
private static object SessionScopeCallback(IContext context)
{
if (HttpContext.Current.Session[_sessionKey] == null)
{
HttpContext.Current.Session[_sessionKey] = new object();
}
return HttpContext.Current.Session[_sessionKey];
}
}