In a code I'm refactoring, I have the following situation:
void Plugin(IExternalService service)
{
var facade = new Facade(
new ExternalServiceWrapper(service),
new Dependency1(),
new Dependency2());
}
Where Dependency1 and Dependency2 are implementations of IDependency1 and IDependency2.
How can I convert this to a registration within Windsor installer? I can't seem to figure our how to pass the instance of IExternalService to the container.
EDIT I'm not in control of the Plugin's creation. I'd like to use it as a composition root to wire all the dependencies.
To register an existing instance, you can use the Instance method:
container.Register(Component.For<IExternalService>().Instance(service));
Related
I am not sure how to use Dependency Injection on Xamarin Android project solution. Currently my Android solution holds a reference to another class library solution. I have used Unity on my service layer and registered the container via WebApiConfig.cs.
My question is, how do i go about using Unity on Android side in order to run on start up, would be grateful if code was included. I dont want to new-up the container through main activity of Android. I want the container to register behind the process i.e. AppStart or Global asax where it does it for you for MVC apps. Is there a way to do it for Android? Also I noticed on Main Activity I am unable to create constructor. I guess this isnt possible but how do I go about holding object reference to my Class Library solution ? example that i attempted to do:
private IExample _ex;
MainActivity(IExample ex){
_ex = ex; //depedency Injection rather than newing it up
}
public void DoSomething(){
_ex.HelloWorld();
}
Is there a way to do it via Attribute ? Also for each of my layer do I need to install and create container in order to resolve current solution dependency ? or can I use container from android which would resolve all dependency in each layer as DDD architecture goes from outer to inner ?
In terms of setting up DI at startup you can create a custom Application implementation like so:
// Must include this attribute so that Android knows we want to use this as our Application implementation
[Application(Icon = "#drawable/Icon", Label = "#string/ApplicationName")]
public class MyApplication : Application
{
public override void OnCreate()
{
base.OnCreate();
// Do your DI initialization/registration here
}
}
I'm not sure exactly what you mean by not being able to create a constructor on the main activity. You can create constructors for any activity you feel like. You don't always see it though because people tend to put their initialization logic in OnCreate.
In normal ASP.MVC projects we configure the dependency resolver with Unity and the Unity.Mvc3 package from http://unitymvc3.codeplex.com/
We have this test service registered with a HierarchicalLifetimeManager
container.RegisterType<ITestService, TestService>(new HierarchicalLifetimeManager());
And we hook up the container with Mvc in Global.asax.cs:
System.Web.Mvc.DependencyResolver.SetResolver(new Unity.Mvc3.UnityDependencyResolver(container));
And we run this test controller:
public class TestController : Controller
{
private readonly ITestService _service;
public TestController(ITestService service)
{
this._service = service;
}
public ActionResult Test()
{
var locatedService = System.Web.Mvc.DependencyResolver.Current.GetService<ITestService>();
if (_service == locatedService)
return View("Success - Same Service");//This is always the result in an MVC controller
else
throw new Exception("Failure - Different Service Located");//This is never the result in an MVC controller
}
}
However, on this project we are adding a number of WebAPI controllers.
We have this configuration in global.asax.cs (using http://unitywebapi.codeplex.com/ for now. But I am open to suggestions):
System.Web.Http.GlobalConfiguration.Configuration.DependencyResolver = new Unity.WebApi.UnityDependencyResolver(container);
We have created an ApiTestController similar to TestController inheriting from ApiController rather than from Controller.
However, the ApiTestController fails its test. I understand that the System.Web.Mvc.DependencyResolver class and the System.Web.Mvc.DependencyResolver.Current property are specific to Mvc. But does WebAPI have an equivalent?
System.Web.Http.GlobalConfiguration.Configuration.DependencyResolver.GetService does not work because the System.Web.Http.GlobalConfiguration.Configuration.DependencyResolver instance is the parent container that I configured. It is not the child controller that was used to inject the ITestService into the constructor.
This user seems to have a similar problem: http://unitywebapi.codeplex.com/discussions/359413
But I feel that this probably has more to do with ASP.NET's WebAPI than it has to do with Unity.
Thanks
After looking over the source of http://unitymvc3.codeplex.com/ and http://unitywebapi.codeplex.com/ I created this class:
public class MyUnityDependencyResolver : Unity.Mvc3.UnityDependencyResolver, System.Web.Http.Dependencies.IDependencyResolver
{
public MyUnityDependencyResolver(IUnityContainer container)
: base(container)
{
}
public System.Web.Http.Dependencies.IDependencyScope BeginScope()
{
return this;
}
public void Dispose()
{
Unity.Mvc3.UnityDependencyResolver.DisposeOfChildContainer();
}
}
Configuration in gobal.asax.cs:
var myResolver = new MyUnityDependencyResolver(container);
System.Web.Mvc.DependencyResolver.SetResolver(myResolver);
System.Web.Http.GlobalConfiguration.Configuration.DependencyResolver = myResolver;
Unity.Mvc3.UnityDependencyResolver uses HttpContext.Current.Items to manage child containers. MyUnityDependencyResolver may not be the most "correct" implementation of System.Web.Http.Dependencies.IDependencyResolver, but it seems to work so far.
I will mark this as the answer in a couple days if no one else has any better answers.
Unfortunately, when you call the GlobalConfiguration.Configuration.DependencyResolver.GetService, it completely ignores any scope and resolves using the outer non-child container which is around for the lifetime of the application. This is an issue with Web Api and makes it impossible to use constructor injection for per-request dependencies outside of controllers. Confusingly this is completely different behaviour from MVC as you say.
What you can do is use the GetDependencyScope() extension method off HttpRequestMessage. Anything you resolve using this will be in per request scope when using HierarchicalLifetimeManager in conjunction with Unity.WebApi. The request is available from action filters and handlers so may be a viable workaround.
Obviously this is pure service location rather than dependency injection which is far from ideal but I have not found another way to access per-request dependencies outside of controllers.
See this post for more info.
The DependencyResolver is not the right seam for dependency injection in ASP.NET WebAPI.
Mark Seemann has two really good posts on DI with WebAPI.
Dependency Injection and Lifetime Management with ASP.NET Web API
Dependency Injection in ASP.NET Web API with Castle Windsor
If you want to do it right you should have a look at them.
I'm trying to get myself familiar with MVC3 and autofac but I've encountered small problem that I'm having trouble resolving.
I am using autofac integrated with MVC3 and all works well, pages are loading correctly, dependencies are being injected and that's cool. What's bugging me is how to use autofac's Container or MVC's DependencyResover in class library project.
I'm trying to create static class that will help me handle domain events. I simply want to be able to call the method with event parameter and everything should be handeled by this class. Here is code:
public static IContainer Container { get; set; }
public static void Raise<T>(T e) where T : IDomainEvent
{
foreach (var eventHandler in DomainEventManager.Container.Resolve<IEnumerable<EventHandlers.Handles<T>>>())
{
eventHandler.Handle(e);
}
}
As you can see it's pretty straightforward and everything would work great if it wasn't MVC approach. Some of my dependencies are registeres as InstancePerHttpRequest (NHibernate' session), while other are registered as InstancePerDependency or SingleInstance. Thus when I try to use container created in my UI project, I get exception that there is no httpRequest tag available.
How can i reuse the Container created in web project to get access to all of it's features, including InstancePerHttpRequest and httpRequest tag?
Or maybe there is other solution to my problem? I was thinking about using delegate function to obtain event handlers, but I cannot (can I?) create generic delegate that I would not need to initialize with concrete type at time of assignment.
Why I want to do this using static class is basically every entity and aggregate or service needs to be able to raise domain event. Injecting EventManager into every one of these would be troublesome and static class is exactly what would resolve all my problems.
If anyone could help me get my head around it I would be grateful.
Cheers, Pako
You shouldn't be referencing your container directly from your app code. This looks like the Service Locator anti-pattern. The correct action is to pass your objects the services they need to do their jobs, usually done through constructor parameters. BUT... if you are going to insist on depending on a global static, then at least model EventManager as a singleton, such that usage would look like:
EventManager.Current.Raise<SomeEvent>(someObject);
and then you can set EventManager.Current equal to a properly constructed instance when your app is initialized.
I am swapping out the standard Unity container in Prism 4 and run into a problem when my modules are initializing. Before I used to get an IUnityContainer injected and this then allowed me to register additional types from my module all well and good.
Now I am injecting an AutoFac.IContainer and it does not have the RegisterType methods i need. They are located in the ContainerBuilder class.
So the simple question is how to I register types into my main container from within my modules as they are loaded.
Thanks
Craig
The standard Autofac way is building your modules as IModule classes, using builder.RegisterModule to load them into your container as part of the register process.
If you already have a container and need to add registrations to it, you use the ContainerBuilder again like this:
var cb = new ContainerBuilder();
cb.Register(...);
...
cb.Update(existingContainer);
It seems like at least 90+% of the Controller Actions I am writing will need to access the database. To me it seems like a logical step to have the database context automatically injected.
I have never used dependency injection before so I want to confirm this is something that is a pattern. If it is, how should I go about doing this? I know ASP.NET MVC 3 has "improved dependency injection" support, but do I still need an external framework? If so what is the default and how do I configure it to create a new database context per http request?
ASP.NET MVC 3 doesn't have improved DI support - it has improved support for the Service Locator anti-pattern (go figure). Fortunately it has had support for DI since MVC 1 through the IControllerFactory interface.
To answer the question, however, yes, it sounds like a perfectly normal thing to inject a Repository into a Controller (although normally we would slide a Domain Model in between the two).
This is best done with Constructor Injection like this:
public class MyController
{
private readonly IMyRepository repository;
public MyController(IMyRepository repository)
{
if (repository == null)
{
throw new ArgumentNullException("repository");
}
this.repository = repository;
}
public ViewResult MyAction(int barId)
{
var bar = this.repository.SelectBar(barId);
return this.View(bar);
}
}
You'll need to provide a custom IControllerFactory to enable Constructor Injection with the MVC framework - the easiest thing is to derive from DefaultControllerFactory.
Once you have a custom IControllerFactory, you can register it in Global.asax like this:
ControllerBuilder.Current.SetControllerFactory(new MyControllerFactory());