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3. The simplest way to implements Dependency Injection in ASP.NET MVC 5 is to use the tool developed by Microsoft itself, called Unity. You can find many resources on the internet about it, and you can start by reading the official documentation available here: Developer's Guide to Dependency Injection Using Unity.
13. Dependency Injection is not integrated by default in classic asp.net, you need to add a nuget package to handle DI (only integrated by default in asp.net core and later versions). Snipsnipsnip added an implementation example below with a Microsoft nuget package. Many 3rd party packages work too.
Like wise dependency injection is the process of externalizing the dependencies to focus only on the specific functionality of the component so that independent components can be coupled together to form a complex system. The main benefits we achieved by using dependency injection. High cohesion and loose coupling.
The use of property injection is fragile, since it results in Temporal Coupling, which should be prevented. Dependency injection into attributes makes it impossible to verify the correctness of the container's configuration. Frameworks like MVC and Web API cache attributes, making it very easy to accidentally create captive dependencies causing ...
8. Have an interface abstract HttpContext.Current. Expose only the methods you need. GetUserName() would call HttpContext.Current.User.Identity.Name in the implementation, for example. Make that as thin as possible. Take that abstraction and inject it into your other provider class.
You can use Service Locator: 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.
From the package manager console run this command: Install-package Ninject.MVC3. This will add a class to App_Start/NinjectWebCommon.cs. If you look near the bottom there is a RegisterServices method. You simply add the code from your question there i.e.
+1, although the service locator is considered an anti-pattern by many, I think I prefer your approach over Marks for its simplicity and also the fact that the dependency is resolved in one place, the IOC container, whereas in Mark's example you would have to resolve in two places, in the bootstrapper and when registering the global filters, which feels wrong.
With this design, I plug in the SampleDbContext as a service in the startup.cs once, and then for each Controller (that receives Dependency Injection) I instantiate a corresponding Repository passing along a new instance of the SampleDbContext. Is this repetitive instantiation of the DB context a good design for a multi-user environment?
So I am using Unity MVC-4 for achieving Dependency Injection and it works great with my Controller classes but as soon as I try to inject in my non controller class, I get the NullReferenceException and I can see that my injected objects are not initialized by the framework. I will give you the corresponding classes that I am using: