Trying to wrap my head around dependency injection, coming from the world of static classes and instantiated classes. Here is what I currently have:
[SomeFilter]
public class AController : Controller
{
private readonly IOptions<AppSettings> _appSettings;
public AController(IOptions<AppSettings> appSettings)
{
_appSettings = appSettings;
}
// GET: /characters/
public IActionResult Index()
{
//do something
}
SomeFilter gets called immediately, and does this:
public class SomeFilter: ActionFilterAttribute, IActionFilter
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
OtherClass.RunMe();
}
}
OtherClass looks like this:
public class OtherClass
{
private readonly IOptions<AppSettings> _appSettings;
public OtherClass(IOptions<AppSettings> appSettings)
{
_appSettings = appSettings;
}
public RunMe()
{
//do something
}
I also have OtherClass registered as a service.Singleton in the Startup.cs.
I get an error stating:
"An object reference is required for a non-static field"
for the OtherClass.RunMe(); call.
I was under the assumption that I can call this class from anywhere within my code instead of having to create a new instance of it? Essentially, how do I call methods from other classes using dependency injection?
You can't constructor injection on filters. It's all about run time order. When you try injection on constructor, your IoC container not reachable at the moment. You should be use property/setter injection.
I prefer using structuremap container for to do this. Because structuremap has very easy to apply any type injection. For example when you have a filter registry like this
public class ActionFilterRegistry : Registry
{
public ActionFilterRegistry(Func<IContainer> containerFactory)
{
For<IFilterProvider>().Use(
new StructureMapFilterProvider(containerFactory));
Policies.SetAllProperties(x =>
x.Matching(p =>
p.DeclaringType.CanBeCastTo(typeof(ActionFilterAttribute)) &&
p.DeclaringType.Namespace.StartsWith("YourNameSpace") &&
!p.PropertyType.IsPrimitive &&
p.PropertyType != typeof(string)));
}
}
And you register it on your global.asax(prefer) or one of your startup class.
Example app_Start method.
DependencyResolver.SetResolver(new StructureMapDependencyResolver(() => Container ?? ObjectFactory.Container));
ObjectFactory.Container.Configure(cfg =>
{
cfg.AddRegistry(new StandardRegistry());
cfg.AddRegistry(new ControllerRegistry());
cfg.AddRegistry(new ActionFilterRegistry(() => Container));
cfg.AddRegistry(new MvcRegistry());
});
Then you can use any filter with injection. But pay attention you shouldn't be use contructor injection like you do.
I found a way to inject into the filter by using
[ServiceFilter(typeof(MyFilter))]
instead of just
[MyFilter]
and within the filter's
(ActionExecutingContext context)
{
var controller = context.Controller as Controller.
controller.whateverIneed
}
This now provides me with what I need within the filter. What I also realized is that I can't remove the need for creating references to other classes using new, as I was under the impression Core's dependency was all about "no more new". This gets into fundamentals with Core which I'm still grasping with.
What I ended up doing was creating new classes that do some work, but they are setup as services and registered in the startup.cs. I'm still grappling on how to intermingle registered services (which I can inject) and new instances of worker classes (which usually hold static information), and passing information between them all.
Related
I'm having trouble injecting the dependency I pass into the constructor of my Asegurador class.
When I want to instantiate, _instance = new Asegurador(); I don't have the parameter required by the constructor (IGeneralRepository), how can I solve this problem?
Note that my Asegurador class is a singleton.
private Asegurador(IGeneralRepository generalRepository)
{
_token = GetTokenAsync().Result;
_repository = generalRepository;
}
public static Asegurador Instance
{
get
{
if (_instance == null)
{
_local = System.Environment.GetEnvironmentVariable("SEGUROS_LOCAL") ?? "local";
_instance = new Asegurador();
}
return _instance;
}
}
When using a DI container you can (and should) let it take care of handling the Lifetime of a dependency.
.Net core's dependency injection lets you define 3 different lifetimes for your services (Docs):
Transient: a transient service is recreated each time it is injected
Scoped: a scoped service is created once for each request
Singleton: a singleton is created once in the whole application lifetime.
The best approach to achieve what you are trying to do is the following:
Amend your Asegurador class so that it has a public constructor and get rid of the static Instance property
public class Asegurador {
public Asegurador(IGeneralRepository generalRepository)
{
_token = GetTokenAsync().Result; //I know too few about it but I would try to pass it as a dependency as well
_repository = generalRepository;
}
}
instead of calling Asegurador.Instance inject the dependency in the client class
public class IUseTheAsegurador {
private Asegurador _asegurador;
public IUseTheAsegurador(Asegurador asegurador)
{
_asegurador = asegurador;
}
}
Register all in the DI in your Startup.cs:
public void ConfigureServices(IServiceCollection services)
{
...
services.AddSingleton<Asegurador>();
services.AddScoped<IUseAsegurador>(); //This can be Singleton or Transient as well, depending on your needs
...
}
I (a lot of people actually :D) prefer this approach because it leaves the responsability of guaranteeing a single instance to the DI and also because lets you write unit tests for the client class (IUseTheAsegurador in the example) in an easier way.
My theme has some sort of breadcrumb. The controller is always the category. To avoid repeat myself, I want to set it in the constructor of the controller for all actions like this:
class MyController:Controller{
public MyController() {
ViewBag.BreadcrumbCategory = "MyCategory";
}
}
When I access ViewBag.BreadcrumbCategory in the layout-view, its null. In a Action it works:
class MyController:Controller{
public IActionResult DoSomething() {
ViewBag.BreadcrumbCategory = "MyCategory";
}
}
I'm wondering that setting a ViewBag property is not possible in a constructor? It would be annoying and no good practice to have a function called on every action which do this work. In another question using the constructor was an accepted answear, but as I said this doesn't work, at least for ASP.NET Core.
There is an GitHub issue about it and it's stated that this is by design. The answer you linked is about ASP.NET MVC3, the old legacy ASP.NET stack.
ASP.NET Core is written from scratch and uses different concepts, designed for both portability (multiple platforms) as well as for performance and modern practices like built-in support for Dependency Injection.
The last one makes it impossible to set ViewBag in the constructor, because certain properties of the Constructor base class must be injected via Property Injection as you may have noticed that you don't have to pass these dependencies in your derived controllers.
This means, when the Controller's constructor is called, the properties for HttpContext, ControllerContext etc. are not set. They are only set after the constructor is called and there is a valid instance/reference to this object.
And as pointed in the GitHub issues, it won't be fixed because this is by design.
As you can see here, ViewBag has a dependency on ViewData and ViewData is populated after the controller is initialized. If you call ViewBag.Something = "something", then you it will create a new instance of the DynamicViewData class, which will be replaced by the one after the constructor gets initialized.
As #SLaks pointed out, you can use an action filter which you configure per controller.
The following example assumes that you always derive your controllers from Controller base class.
public class BreadCrumbAttribute : IActionFilter
{
private readonly string _name;
public BreadCrumbAttribute(string name)
{
_name = name;
}
public void OnActionExecuting(ActionExecutingContext context)
{
base.OnActionExecuting(context);
var controller = context.Controller as Controller;
if (controller != null)
{
controller.ViewBag.BreadcrumbCategory = _name;
}
}
}
Now you should be able to decorate your controller with it.
[BreadCrumb("MyCategory")]
class MyController:Controller
{
}
I have the same issue and solve it overriding the OnActionExecuted method of the controller:
public override void OnActionExecuted(ActionExecutedContext context)
{
base.OnActionExecuted(context);
ViewBag.Module = "Production";
}
Here is a better way to do this for .NET Core 3.x, use the ResultFilterAttribute:
Create your own custom filter attribute that inherits from ResultFilterAttribute as shown below:
public class PopulateViewBagAttribute : ResultFilterAttribute
{
public PopulateViewBagAttribute()
{
}
public override void OnResultExecuting(ResultExecutingContext context)
{
// context.HttpContext.Response.Headers.Add(_name, new string[] { _value });
(context.Controller as MyController).SetViewBagItems();
base.OnResultExecuting(context);
}
}
You'll need to implement the method SetViewBagItems to populate your ViewBag
public void SetViewBagItems()
{
ViewBag.Orders = Orders;
}
Then Decorate your Controller class with the new attribute:
[PopulateViewBag]
public class ShippingManifestController : Controller
That's all there is to it! If you are populating ViewBags all over the place from your constructor, then you may consider creating a controller base class with the abstract method SetViewBagItems. Then you only need one ResultFilterAttribute class to do all the work.
I'm trying to inject business logic implementations into web API base controller. Somehow property in base controller is always null.
Also how can I do lazy injection?
Startups.cs
public IServiceProvider ConfigureServices(IServiceCollection services)
{
// Add framework services.
services.AddMvc();
var containerBuilder = new ContainerBuilder();
containerBuilder.RegisterType<ViewBusinessLogic>().As<IViewBusinessLogic>().
PropertiesAutowired();
containerBuilder.Populate(services);
var container = containerBuilder.Build();
return container.Resolve<IServiceProvider>();
}
Interface, implementation and base controller:
public interface IViewBusinessLogic
{
IEnumerable<dynamic> GetView(Guid viewId);
}
public class ViewBusinessLogic : BusinessLogic, IViewBusinessLogic
{
public IEnumerable<dynamic> GetView(Guid viewId)
{
return new List<dynamic>
{
new { Test = "Test1" },
new { Test = "Test2" }
};
}
}
public abstract class BaseController : Controller
{
public IViewBusinessLogic ViewBusinessLogic { get; }
}
Controllers aren't resolved by the DI framework by default. You need to add AddControllerAsServices to have them be resolved by the DI of your choice.
From this GitHub issue:
Hi,
Maybe I'm wrong but as I tested deeply (and checked Mvc source code), Controllers are not resolved from IServiceProvider, but only constructor arguments of them are resolved from IServiceProvider.
Is that by design? I'm very suprised. Because, I'm using a different DI framework which supports property injection. And I can not use property injection since Controller instances are not requested from IServiceProvider.
Have you added AddControllersAsServices in your Startup (https://github.com/aspnet/Mvc/blob/ab76f743f4ee537939b69bdb9f79bfca35398545/test/WebSites/ControllersFromServicesWebSite/Startup.cs#L37)
The example above quoted for future reference.
public void ConfigureServices(IServiceCollection services)
{
var builder = services
.AddMvc()
.ConfigureApplicationPartManager(manager => manager.ApplicationParts.Clear())
.AddApplicationPart(typeof(TimeScheduleController).GetTypeInfo().Assembly)
.ConfigureApplicationPartManager(manager =>
{
manager.ApplicationParts.Add(new TypesPart(
typeof(AnotherController),
typeof(ComponentFromServicesViewComponent),
typeof(InServicesTagHelper)));
manager.FeatureProviders.Add(new AssemblyMetadataReferenceFeatureProvider());
})
// This here is important
.AddControllersAsServices()
.AddViewComponentsAsServices()
.AddTagHelpersAsServices();
services.AddTransient<QueryValueService>();
services.AddTransient<ValueService>();
services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
}
As for the second part of your question: I don't think it's possible to have lazy instantiation via IoC container at all. Best fit for you is to create a factory class and inject the factory rather than the concrete service.
But usually you don't need lazy instantiation anyways, the instantiation of services should be fast. If it's not, you probably doing some funky stuff in the constructor (connecting somewhere, or doing other long running operations), which is an anti-pattern.
In my application i configured structuremap like
public class DefaultRegistry : Registry {
#region Constructors and Destructors
public DefaultRegistry() {
Scan(
scan => {
scan.Assembly("Eterp.Data.ErpCore");
scan.Assembly("Eterp.Data.Seed");
scan.Assembly("Eterp.Application.ErpCore");
scan.TheCallingAssembly();
scan.WithDefaultConventions();
});
ForConcreteType<AclAuthorizationManager>().Configure.Ctor<IResourceOperationAppService>()
}
#endregion
}
And i have class
public class AclAuthorizationManager : ClaimsAuthorizationManager
{
private readonly IResourceOperationAppService _resourceOperationAppService;
public AclAuthorizationManager(IResourceOperationAppService resourceOperationAppService)
{
_resourceOperationAppService = resourceOperationAppService;
}
public override bool CheckAccess(AuthorizationContext context)
{
var isCurrentUserAuthorized = context.Principal.Identity.IsAuthenticated;
return isCurrentUserAuthorized && _resourceOperationAppService.CanAccessResource(context.Action.FirstOrDefault().Value, context.Principal.Claims);
}
}
This class is custom claim authorization class using in my application, but when i exceuting the application,i am getting an error which related to lack of parameter required by the constructor, ( This class has constructor with parameter type IResourceOperation). but i already configured all the details in structureMap . i am sure that my structuremap configuration is working 100% well expect the creation of this AclAuthorizationManager class.because i am able to to apply DI in other classes.
What is wrong part in my code?
in my experience when you specify the type constructor must say that inherits from the interface.
Therefore, you should replace this line:
ForConcreteType<AclAuthorizationManager>().Configure.Ctor<IResourceOperationAppService>()
By:
ForConcreteType<AclAuthorizationManager>().Configure.Ctor<IResourceOperationAppService>().Is<ResourceOperationAppService>()
Where is the implementation ResourceOperationAppService IResourceOperationAppService.
This is my first try using DI, I've chosen ninject for it's reportedly easy learning curve, and have this question.
I'm creating objects like this:
var registrants = JsonConvert.DeserializeObject<List<Registrant>>(input);
I currently have this constructor for Registrant
[Inject]
public Registrant(IMemberRepository memberRepository)
{
_memberRepository = memberRepository;
}
What is the best way to have the repository dependency be injected into the deserialized object(s) using Ninject?
You can't use constructor injection with objects that are not created by Ninject (e.g. deserialized objects). But you can use property injection. Just call kernel.Inject(obj)
One question that remains is why you want to inject those objects. Normally, you don't want to use depedency injection on data container objects. In a proper design they don't have any dependency on services. The operations that need to be done on the services are done by the owner of the data container objects. I recommend to consider a refactoring of your design.
Assuming you're using Ninject V2, and you're using it in the context of an ASP.NET app, you should be using Ninject.Web to do the hookups.
Then you set up a Global class with the Factory Method support hooked in:
public class Global : NinjectHttpApplication
{
protected override Ninject.IKernel CreateKernel()
{
var kernel = new StandardKernel( new Module() );
kernel.Components.Add( new FuncModule( ) );
return kernel;
}
}
that registers the module that will Bind IMemberRepository to something:
public class Module : NinjectModule
{
public override void Load()
{
Bind<IMemberRepository>().To<MemberRepository>();
}
}
and the page wires up like this:
public class ThePage : PageBase
{
readonly Func<Registrant> _createRegistrant;
public ThePage( Func<Registrant> createRegistrant )
{
_createRegistrant = createRegistrant;
}
private void OnCreateRegistrant()
{
var newRegistrant = _createRegistrant();
}
}
NB not 100% sure if constructor injection is supported for Web Forms pages or wheter the above needs to drop to property injection... anyone?
(assuming the classes you have are as follows:)
public class MemberRepository : IMemberRepository
{
}
public interface IMemberRepository
{
}
public class Registrant
{
private readonly IMemberRepository _memberRepository;
public Registrant( IMemberRepository memberRepository )
{
_memberRepository = memberRepository;
}
}