Develop Reference

DI Constructor Injection Neatness

Okay so I am looking for some specific tips about Dependency Injection and how to use it.
Basically I have a MVC website which uses Ninject (and the Ninject MVC package). So when I am creating the MVC page I use constructor injection in the controllers. This is okay but IMO a bit 'ugly', but the main thing I don't like is having to pass all of the injected repositories into the other classes, it just seems a bit OTT having to pass like 6 repositories-8 repositories into a static method or object constructor.
Not to mention that on some of my pages I am having to work on almost every repository so the controller consructor gets huge and not the most manageable.
Are there any other options that wont clutter my code up as much? I don't really want to pass them in as single 'setting' objects either as that just moves the problem to a different line of code.
I also use the same class libraries for console/desktop applications. I like the idea of using DependencyResolver.Current in the class libraries but everyone says this is an anti-pattern and constructor injection should be used.
Maybe have an MyProjectDIContext class which has a dictionary which i can populate with the injected types in the controller constructors then pass the context to all methods as needed?
I have had a look for the answer bit I can't quite seem to find something that fits well.

One of the great things about Constructor Injection is that it makes design and maintainability problems more obvious. When using constructor injection, it becomes very easy to see the amount of dependencies a class has, whereas without constructor injection, a class still has the same number of dependencies, but they are tucked away.
The problem you are seeing is called Constructor Over-injection and it's a design smell, because it indicates that you are violating the Single Responsibility Principle (SRP). The SRP guides in keeping your classes small, focussed and most of all: maintainable.
Are there any other options that wont clutter my code up as much?
Absolutely: make smaller classes. MVC controllers typically get huge when we use it to group methods of a certain concept, such as 'customer' or 'order'. This however means that a controller is an ever growing class that has to be changed for any new feature that arrives. This is a violation of the Open/closed Principle that tells we should strive to have a system where we can plugin new features without having to touch existing classes.
The solution therefore is not to revert to the Service Locator anti-pattern or Property Injection, but to create smaller classes that do one particular thing. Constructor Injection should be your primary way of applying Dependency Injection, even in class libraries.

It seems that your controller is shuffling repositories to other classes. Let Ninject supply those classes to you instead:
public class Controller
{
public Controller(IDependencyFactory dependency) { }
}
public interface IDependencyFactory
{
IDependency CreateDependency();
}
public interface IDependency
{
}
public class Dependency : IDependency
{
public Dependency() { }
}
public class Program
{
public static void Main()
{
var standardKernel = new StandardKernel();
standardKernel.Bind<IDependencyFactory>().ToFactory();
standardKernel.Bind<IDependency>().To<Dependency>();
}
}
You don't have to write an implementation of IDependencyFactory, that is handled by the factory extension. Your Dependency-class will get it's dependencies injected by Ninject.

Okay I seem to have found a way to do this which doesn't seem as smelly!
I had thought that if you are for example using MVC you would get the Repositories in through the constructor and that was the only way to resolve the dependencies.
After doing some work to move sections of reusuable code into IoC friendly Interfaces and their implementations I noticed that when you create reference IMyInterface in a controller constructor the default constructor of the implementing class is run and you can pull other IoC classes such as resolved repositories from there.
This may be common knowledge but it does make things much much neater and solves the problem I was having.
Example
Controller
public IDefaultTemplateManager DefaultTemplateManager { get; set; }
public DefaultController(IDefaultTemplateManager defaultTemplateManager) {
this.DefaultTemplateManager = defaultTemplateManager;
}
public ActionResult MyAction(FormCollection collection) {
DefaultTemplateManager.Process("MyKeyHere");
View();
}
IDefaultTemplateManager
public interface IDefaultTemplateManager {
ProcessResponse Process(string UniqueKey, DefaultTemplateManagerEditMode DatabaseName, string DefaultTemplateName);
}
DefaultTemplateManager
public class DefaultTemplateManager : IDefaultTemplateManager {
protected IRepository<MyEntity1> MyEntityRepo1 { get; set; }
protected IRepository<MyEntity2> MyEntityRepo2 { get; set; }
protected IRepository<MyEntity3> MyEntityRepo3 { get; set; }
protected IRepository<MyEntity4> MyEntityRepo4 { get; set; }
protected IRepository<MyEntity5> MyEntityRepo5 { get; set; }
protected IRepository<MyEntity6> MyEntityRepo6 { get; set; }
public DefaultTemplateManager(IRepository<MyEntity1> MyEntityRepository1, IRepository<MyEntity2> MyEntityRepository2, IRepository<MyEntity3> MyEntityRepository3, IRepository<MyEntity4> MyEntityRepository4, IRepository<MyEntity5> MyEntityRepository5, IRepository<MyEntity6> MyEntityRepository6, ) {
this.MyEntityRepo1 = MyEntityRepository1;
this.MyEntityRepo2 = MyEntityRepository2;
this.MyEntityRepo3 = MyEntityRepository3;
this.MyEntityRepo4 = MyEntityRepository4;
this.MyEntityRepo5 = MyEntityRepository5;
this.MyEntityRepo6 = MyEntityRepository6;
}
public ProcessResponse Process(string UniqueKey) {
/* Do Work */
}

Using Simple Injector with Umbraco Controller

I'm trying to Inject a dependency into a controller which inherits from Umbraco's RenderMvcController and getting the error
No registration for type RenderMvcController could be found and an implicit registration could not be made. For the container to be able to create RenderMvcController it should have only one public constructor: it has 3. See https://simpleinjector.org/one-constructor for more information.
Below is my code to wire up the DI
var container = new Container();
container.Options.DefaultScopedLifestyle = new WebRequestLifestyle();
InitializeContainer(container);
container.RegisterMvcControllers(Assembly.GetExecutingAssembly());
container.Verify();
DependencyResolver.SetResolver(new SimpleInjectorDependencyResolver(container));
private static void InitializeContainer(Container container)
{
container.Register<ICacheProvider, CacheProvider>(Lifestyle.Transient);
container.Register<ICacheService, CacheService>(Lifestyle.Transient);
}
This is an example of a class receiving the dependency, it inherits from a base class I wrote
public class NewsroomController : BaseRenderMvcController
{
public NewsroomController(ICacheService cacheService) : base(cacheService) { }
The base class extends RenderMvcController which is an Umbraco Controller
public class BaseRenderMvcController : RenderMvcController
{
public ICacheService CacheService { get; set; }
public BaseRenderMvcController(ICacheService cacheService)
{
CacheService = cacheService;
}
}
As you can see the base Umbraco controller does in fact have 3 different constructors
public class RenderMvcController : UmbracoController, IRenderMvcController, IRenderController, IController
{
public RenderMvcController();
public RenderMvcController(UmbracoContext umbracoContext);
public RenderMvcController(UmbracoContext umbracoContext, UmbracoHelper umbracoHelper);
I'm not sure how to get SimpleInjector to place nicely with this controller inherited from Umbraco.
Thanks in advance!

The exception message "No registration for type RenderMvcController could be found and an implicit registration could not be made" means that the RenderMvcController type is requested directly from Simple Injector, while it hasn't been registered. A controller type is usually only requested by the DefaultControllerFactory and it will only request a specific type when it gets a request that has the name of the controller in its url, as in: http:\\localhost\RenderMvc\3.
Since you stated in the comments that the RenderMvcController is only meant to be used as base controller, I find it suspicious that it is actually requested by MVC. I think you should look into that.
But it the use of this controller is really required, you can simply register it in Simple Injector like this:
container.Register<RenderMvcController>(() => new RenderMvcController());
There are ways to override Simple Injector's constructor resolution behavior, but I would advise against doing this, because it is an anti-pattern for components to have multiple constructors. It's wise to don't use a container's auto-wiring behavior on framework types (as explained here), so registering them using a lambda is the advised practice.

Modern UI wpf, how to add ContentSource page with constructor injection as view model

Im pretty new to modern ui framework. I'm adding new page(usercontroller) as ContentSource page.
Im using IOC framework (IviewModels and ViewModels). I'm getting error saying no maching constructor found. because usercontroll default constructor injected with Iviewmodel object.
i'm pretty stuck here, it would be great some one can help this matter
thanks
this is my main window code + this is my usercontroll cs file
this is the error

As you found out, you can't use parameterized constructors because they break the framework.
Navigation use just the page URI, no other extra parameters.
So, how do you use IoC without parameterized constructors?
You should use a Dependency Injection Container.
Something like this:
public partial class MyPage: UserControl
{
private MyViewModel: IViewModel;
public MyPage()
{
MyViewModel = MyViewModelFactory.Create(IViewModel);
InitializeComponent();
}
}
MyVewModelFactory is an object which create other objects.
You dont have to code it by yourself.
Some common IoC containers are:
Unity
MEF
Using Unity your code would be:
public partial class MyPage: UserControl
{
private MyViewModel: IViewModel;
public MyPage()
{
MyViewModel = container.Resove<IViewModel>();
InitializeComponent();
}
}
Using MEF your code would be:
public partial class MyPage: UserControl
{
[Import(GetType(IViewModel))]
private MyViewModel: IViewModel;
public MyPage()
{
InitializeComponent();
}
}

Dependency Injection / Constructor Injection Help

I have the following classes / interfaces:
public interface IProjectRepository
{
IQueryably<Project> GetProjects();
}
// Depends on my EF Context
public ProjectRepository : IProjectRepository
{
private MyDbEntities context;
public ProjectRepository(MyDbEntities context)
{
this.context = context;
}
public IQueryable<Project> GetProjects()
{
return context.Projects;
}
}
My controller:
// Depends on IProjectRepository
public class ProjectsController : Controller
{
private IProjectRepository projectRepository;
public ProjectsController(IProjectRepository projectRepository)
{
this.projectRepository = projectRepository;
}
public ActionResult Index()
{
return View(projectRepository.GetProjects());
}
}
I need to set up my dependency injection so that it passes in ProjectRepository into my Controller AND it needs to pass in my Entity Framework context into the Project Repository. I need to Entity Context to be HTTP Request scoped.
I'm not sure where I am supposed to put all the mapping code to make the dependency injection work. I also don't understand how MVC will work without the default constructor.
Can someone help me put all the pieces together? I am using StructureMap but I could easily switch to something else because I have no idea what I'm doing.

If you are using MVC 3, to do things properly, you should make use of the built in dependency resolution bits. I would highly recommend you read through the series of blog posts from Brad Wilson (member of the ASP.NET MVC team).
As far as a StructureMap specific implementation, I found the following blog posts helpful.
StructureMap and ASP.NET MVC 3 – Getting Started
StructureMap, Model Binders and Dependency Injection in ASP.NET MVC 3
StructureMap, Action Filters and Dependency Injection in ASP.NET MVC 3
StructureMap, Global Action Filters and Dependency Injection in ASP.NET MVC 3
Anyway, here's some code. To start with, I would suggest that you install the StructureMap-MVC3 NuGet package.
I can't remember what exactly it creates in the way of files, but here's what's basically involved.
/App_Start/StructuremapMvc.cs - This hooks into the Application_Start and sets up your container (SmIoC.Initialize()) and then sets the MVC 3 DependencyResolver to a your SmDependencyResolver
using System.Web.Mvc;
using YourAppNamespace.Website.IoC;
using StructureMap;
[assembly: WebActivator.PreApplicationStartMethod(typeof(YourAppNamespace.App_Start.StructuremapMvc), "Start")]
namespace YourAppNamespace.Website.App_Start {
public static class StructuremapMvc {
public static void Start() {
var container = SmIoC.Initialize();
DependencyResolver.SetResolver(new SmDependencyResolver(container));
}
}
}
/IoC/SmDependencyResolver.cs - this is your MVC 3 IDependencyResolver implementation. It's used in the App_Start code above.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.Mvc;
using StructureMap;
namespace YourAppNamespace.Website.IoC
{
public class SmDependencyResolver : IDependencyResolver
{
private readonly IContainer _container;
public SmDependencyResolver(IContainer container)
{
_container = container;
}
public object GetService(Type serviceType)
{
if (serviceType == null)
{
return null;
}
try
{
return _container.GetInstance(serviceType);
}
catch
{
return null;
}
}
public IEnumerable<object> GetServices(Type serviceType)
{
return _container.GetAllInstances(serviceType).Cast<object>(); ;
}
}
}
/IoC/SmIoC.cs - this is where you setup your container... also used in the App_Start code.
namespace YourAppNamespace.Website.IoC
{
public static class SmIoC
{
public static IContainer Initialize()
{
ObjectFactory.Initialize(x =>
{
x.For<IProjectRepository>().Use<ProjectRepository>();
//etc...
});
return ObjectFactory.Container;
}
}
}
Now everything is hooked up... (I think ;-) but you still have one last thing to do. Inside your Global.asax, we need to make sure you dispose of everything that is HttpContext scoped.
protected void Application_EndRequest()
{
ObjectFactory.ReleaseAndDisposeAllHttpScopedObjects();
}
So you should be able to achieve dependency injection through constructor injection, which is the correct way to go about doing things.

If you are set on using StructureMap, here is a tutorial on the setup that you will probably need.
Some other dependency injection frameworks come with custom controller factories which will do that for you. Ninject (open source dependency injection), for example has an extension that you can use that contains this behaviour. See here for example. And here to the extension.
You can use also Unity IOC which is another popular dependency injection framework with which, to my knowledge, you will have to create a custom controller factory (like with structuremap) to achieve this behaviour. See here for an example.
You can also research all other dependency injection frameworks to see what support you can get with each.
EDIT:
I hope I am explaining this correctly but here is some background info.
MVC uses a controller factory that has the responsibilities of instantiating the respective controllers needed when a request is made. By default, it will initialize a controller by calling its parameterless constructor.
To create the infrastructure for the constructor parameter injection you need to create a custom factory that can resolve constructor parameters. That is where the dependency injection containers come in: essentially the DI container (if configured properly) knows how to resolve those dependency and your custom factory will leverage it to request the registered dependencies and pass the to the controller constructor.

All work pretty much the same. Historically, all have had setter injectors (set up a property that is then filled), but most have constructor injection now. In structure map, the easiest way to accomplish this is use the attribute: [StructureMap.DefaultConstructor].
Once you add the attribute, the objects you have placed in your "map" should inject without any extra work. If you can't use attributes, consider using the setter.
There is a file on the structure map site:
http://structuremap.net/structuremap/ConstructorAndSetterInjection.htm

When using StructureMap I would generally have something like this in my controller:
private static IProjectRepository GetProjectRepository()
{
var retVal = ObjectFactory.TryGetInstance<IProjectRepository>()
?? new ProjectRepository();
return retVal;
}
If the TryGetInstance returns null (because nothing was set for that type) it will default to the concrete type you specify.
Now you have a bootstrapper somewhere like this:
public static class StructureMapBootStrapper
{
public static void InitializeStructureMap()
{
ObjectFactory.Initialize(x =>
{
x.For<IProjectRepository>().Use<ProjectRepository>();
}
}
}
Now you call this bootstrapper in your Global.asax Application_Start event:
protected void Application_Start()
{
StructureMapBootStrapper.InitializeStructureMap();
}
Now in a test project, when you want to inject a mock repository you can just do this:
[TestMethod]
public void SomeControllerTest()
{
StructureMap.ObjectFactory.Inject(
typeof(IProjectRepository),
new MockProjectRepository());
// ... do some test of your controller with the mock
}

dependency injection alternatives

I am looking at depency injection, I can see the benefits but I am having problems with the syntax it creates. I have this example
public class BusinessProducts
{
IDataContext _dx;
BusinessProducts(IDataContext dx)
{
_dx = dx;
}
public List<Product> GetProducts()
{
return dx.GetProducts();
}
}
The problem is that I don't want to write
BusinessProducts bp = new BusinessProducts(dataContextImplementation);
I would continue to write
BusinessProducts bp = new BusinessProducts();
because I feel the first alternative just feels unatural. I dont want to know what the BusinessProduct "depends" on to get the products, also I feel it makes my code more unreadable.
Is there any alternatives to this approach as I would like to keep my original syntax for creating objects but I would like to still be able to fake the dependencies when unit testing or is it this dependecy injection frameworks can do for me?
I am coding in c# but alternatives from other languages is welcome

I use a factory for my context and inject it, providing a suitable default if the provided factory is null. I do this for two reasons. First, I use the data context as a unit of work scoped object so I need to be able to create them when needed, not keep one around. Second, I'm primarily using DI to increase testability, with decoupling only a secondary consideration.
So my business products class would look like:
public class BusinessProducts
{
private IDataContextFactory DataContextFactory { get; set; } // my interface
public BusinessProducts() : this(null) {}
public BusinessProducts( IDataContextFactory factory )
{
this.DataContext = factory ?? new BusinessProductsDataContextFactory();
}
public void DoSomething()
{
using (DataContext dc = this.DataContextFactory().CreateDataContext())
{
...
}
}
An alternative to this would be to make the factory property publicly settable and inject an alternate factory by setting the property. Either way if you want to keep the null constructor, you'll need to provide a default.

You can create a factory. DI containers are best for wirings that happen at setup-time - not at runtime (As this looks to be a case of). Factories can be implemented in different ways, depending on how pluggable it needs to be, and how many places you need to use it.

I would usually have an empty constructor which uses a solid instance( or an instances created by IoC), amd one with DI. i.e.
public class BusinessProducts
{
IDataContext _dx;
BusinessProducts()
{
_dx = new SolidDataContext();
}
BusinessProducts(IDataContext dx)
{
_dx = dx;
}
}
This way you can use DI for overriding the default instance in unit testing testing.

Your feelings, while valid, are misplaced.
The Dependency Injection pattern is a direct application of the Inversion of Control principle.
This means that, instead of your class controlling the instances of other classes it consumes, that relationship is inverted and the dependencies are provided to it.
As such, your classes naturally expose their dependencies via constructor arguments or properties. Showing disdain for this structure says you haven't truly grokked the pattern.

There are two distinct cases here:
In production code you will never write
new BusinessProducts(dataContextImplementation)
because dependency injection will normally be creating the full object hierarchy for you. This is the "viral" nature of dependency injection patterns, they tend to take over full control of your service creation.
In unit test code you will normally be creating this yourself, but quite often you will be supplying a mock object or a stub implementation of dataContextImplementation. So normally you will be injecting an object that does not have a large number of subsequent dependencies.

http://springframework.net/ and http://structuremap.sourceforge.net/Default.htm are probably the mostly used DI frameworks for .NET based languages and will both do what you need.

Generally the framework itself will have the logic to build up the entire object tree. For example, instead of
new SomeObjectO(diContext)
you would call the framework like this:
DIFramework.GetNew<SomeObjectO>();
or
DIFramework.Get<SomeObject>();
Another interesting framework to take a look at if you would like to learn about DI and the process is Microsoft's Unity and Object Builder projects.

If you really do not like injecting this instance in the constructor, you might try to use the CommonServiceLocator with your favourite compatible .NET depedency injection framework. This would allow you to write code like this:
public class BusinessProducts
{
IDataContext _dx;
BusinessProducts()
{
_dx = Microsoft.Practices.ServiceLocation.ServiceLocator.Current.GetInstance<IDataContext>();
}
public List<Product> GetProducts()
{
return dx.GetProducts();
}
}
However, please beware that this is not what most people would expect when they know that you use a dependency injection framework. I think that it is much more common to use a dependency injection framework and letting it create all objects for you.
BusinessProducts bp = Microsoft.Practices.ServiceLocation.ServiceLocator.Current.GetInstance<BusinessProducts>();
If you would like to avoid the dependeny injection framework path, using a factory is probably the best way to go.

There's a technique called poor man's DI that looks like this
public class BusinessProducts
{
IDataContext _dx;
BusinessProducts() : this(new DataContext()) {}
BusinessProducts(IDataContext dx)
{
_dx = dx;
}
public List<Product> GetProducts()
{
return dx.GetProducts();
}
}
This is not ideal since it ties you to the implementation but its a good stepping stone towards decoupled code. this is similar to #tvanfosson but a lot simplier.
I second the recommendation for Windsor

My code will reference Microsoft Unity but I am sure it is pretty applicable to all DI frameworks. If you're using DI correctly you never need to call new BusinessObject(new dataContext) the DI association will handle it all for you.
My example will be a little bit long since I will paste in some code I use for running a Model View Presenter website fully DI loaded by Unity. (If you want the full source check out my blog and download it from my Assembla SVN server)
Load the container (can be in code like I prefer or using configuration)
protected void Application_Start(object sender, EventArgs e)
{
Application.GetContainer()
// presenters / controllers are per request
.RegisterType<IEmployeeController, EmployeeController>(new ContextLifetimeManager<IEmployeeController>())
//Data Providers are Per session
.RegisterType<IEmployeeDataProvider, EmployeeDataProvider>(new SessionLifetimeManager<IEmployeeDataProvider>())
//Session Factory is life time
.RegisterType<INHibernateSessionManager, NHibernateSessionManager>(new ContainerControlledLifetimeManager());
}
Custom HTTP module calls Unity BuildUp Method for each page during the OnPreRequest invocation.
private static void OnPreRequestHandlerExecute(object sender, EventArgs e)
{
var handler = HttpContext.Current.Handler;
HttpContext.Current.Application.GetContainer().BuildUp(handler.GetType(), handler);
// User Controls are ready to be built up after the page initialization is complete
var page = HttpContext.Current.Handler as Page;
if (page != null)
{
page.InitComplete += OnPageInitComplete;
}
}
Page container presenter decorated with [Dependency] attribute
public partial class Employees : Page, IEmployeeView
{
private EmployeePresenter _presenter;
[Dependency]
public EmployeePresenter Presenter
{
set
{
_presenter = value;
_presenter.View = this;
}
}
}
Presenter with InjectionConstructor method
public class EmployeePresenter : Presenter<IEmployeeView>
{
private readonly IEmployeeController _controller;
[InjectionConstructor]
}
public EmployeePresenter(IEmployeeController controller)
{
_controller = controller;
}
Controller follows suit
public class EmployeeController : IEmployeeController
{
private readonly IEmployeeDataProvider _provider;
[InjectionConstructor]
public EmployeeController(IEmployeeDataProvider DataProvider)
{
_provider = DataProvider;
}
}
Same with provider
public class EmployeeController : IEmployeeController
{
private readonly IEmployeeDataProvider _provider;
[InjectionConstructor]
public EmployeeController(IEmployeeDataProvider DataProvider)
{
_provider = DataProvider;
}
}
Lastly the session manager, which contains only a regular constructor.
public class NHibernateSessionManager : INHibernateSessionManager
{
private readonly ISessionFactory _sessionFactory;
public NHibernateSessionManager()
{
_sessionFactory = GetSessionFactory();
}
}
So what happens when a page request is started the BuildUp() method is called on the page by the HttpModule. Unity then sees the Property marked with the Dependency attribute and will check it's container to see if inside it exists an EmployeePresenter object.
Since there is no such object in the container it will then try to create an EmployeePresenter. Upon inspection to create the class it sees inside the Presenter it requires a constructor that needs a IEmployeeController injected into it. Since the container actually has a manager for the controller it will see if an instance of it exists in the container which on the beginning of the page request doesn't exist, so it will go to instantiate the controller.
Unity will then see the controller requires a IEmployeeDataProvider injected into it, and it will continue on this process until it finally gets to the point where the Provider needs the session manager injected. Since the session manager has no more need for injection Unity will then create an instance of the session manager store it in the container for it's given ContainerLifeTimeManager, inject it into the Provider and store that instance, and so on down to where it finished creating a EmployeePresenter dependency for the page.

you can also look at windsor for IoC .