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Inversion of Control and Dependency Injection - I need your advice

i wrote a little example to learn IoC and DI on my own.
I have one simple question:
How would you instantiate the unskilled worker in my example /
How can I swich between the following 2 inject candidates?:
kernal.Bind<IRepair>().To<Employee>();
kernal.Bind<IRepair>().To<UnskilledWorker>()
I'm a little bit confused at the moment...
class Program
{
static void Main(string[] args)
{
IWorkShop instance = GetWorkShop();
instance.StartToRepair();
Console.ReadLine();
}
private static IWorkShop GetWorkShop()
{
Ninject.IKernel kernal = new StandardKernel();
kernal.Bind<IWorkShop>().To<WorkShop>();
kernal.Bind<IRepair>().To<Employee>();
var instance = kernal.Get<IWorkShop>();
return instance;
}
}
public class WorkShop : IWorkShop
{
private IRepair _repair;
public WorkShop(IRepair repair)
{
_repair = repair;
}
public void StartToRepair()
{
_repair.RepairItNow();
}
}
interface IWorkShop
{
void StartToRepair();
}
public class Employee : IRepair
{
public void RepairItNow()
{
Console.WriteLine("Employee starts working.");
}
}
public class UnskilledWorker : IRepair
{
public void RepairItNow()
{
Console.WriteLine("Unskilled worker starts working.");
}
}
public interface IRepair
{
void RepairItNow();
}
}

If you know at compile time then you can use Ninject's contextual bindings: https://github.com/ninject/ninject/wiki/Contextual-Binding.
IKernel kernal = new StandardKernel();
kernal.Bind<IWorkShop>().To<WorkShop>();
kernal.Bind<IRepair>().To<Employee>();
kernal.Bind<IRepair>().To<UnskilledWorker>().WhenInjectedInto(typeof(IWorkShop));
var instance = kernal.Get<IWorkShop>();
return instance;
If you need to decide at runtime which dependency to instantiate you are going to have to use a factory pattern.

Seemann's Dependency Injection, "Three Calls Pattern" vs Service Locator Anit-Pattern

I have created a WinForms MVC application using Dependency Injection (DI) and Ninject as the DI Container. The basic architecture is as follows
Program.cs (the main entry point of the WinForms application):
static class Program
{
[STAThread]
static void Main()
{
...
CompositionRoot.Initialize(new DependencyModule());
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(CompositionRoot.Resolve<ApplicationShellView>());
}
}
DependencyModule.cs
public class DependencyModule : NinjectModule
{
public override void Load()
{
Bind<IApplicationShellView>().To<ApplicationShellView>();
Bind<IDocumentController>().To<SpreadsheetController>();
Bind<ISpreadsheetView>().To<SpreadsheetView>();
}
}
CompositionRoot.cs
public class CompositionRoot
{
private static IKernel ninjectKernel;
public static void Initialize(INinjectModule module)
{
ninjectKernel = new StandardKernel(module);
}
public static T Resolve<T>()
{
return ninjectKernel.Get<T>();
}
public static IEnumerable<T> ResolveAll<T>()
{
return ninjectKernel.GetAll<T>();
}
}
ApplicationShellView.cs (the main form of the application)
public partial class ApplicationShellView : C1RibbonForm, IApplicationShellView
{
private ApplicationShellController controller;
public ApplicationShellView()
{
this.controller = new ApplicationShellController(this);
InitializeComponent();
}
public void InitializeView()
{
dockPanel.Extender.FloatWindowFactory = new CustomFloatWindowFactory();
dockPanel.Theme = vS2012LightTheme;
}
private void ribbonButtonTest_Click(object sender, EventArgs e)
{
controller.OpenNewSpreadsheet();
}
public DockPanel DockPanel
{
get { return dockPanel; }
}
}
where
public interface IApplicationShellView
{
void InitializeView();
DockPanel DockPanel { get; }
}
ApplicationShellController.cs
public class ApplicationShellController
{
private IApplicationShellView shellView;
public ApplicationShellController(IApplicationShellView view)
{
this.shellView = view;
}
public void OpenNewSpreadsheet(DockState dockState = DockState.Document)
{
SpreadsheetController controller = (SpreadsheetController)GetDocumentController("new.xlsx");
SpreadsheetView view = (SpreadsheetView)controller.New("new.xlsx");
view.Show(shellView.DockPanel, dockState);
}
private IDocumentController GetDocumentController(string path)
{
return CompositionRoot.ResolveAll<IDocumentController>()
.SingleOrDefault(provider => provider.Handles(path));
}
public IApplicationShellView ShellView { get { return shellView; } }
}
SpreadsheetController.cs
public class SpreadsheetController : IDocumentController
{
private ISpreadsheetView view;
public SpreadsheetController(ISpreadsheetView view)
{
this.view = view;
this.view.SetController(this);
}
public bool Handles(string path)
{
string extension = Path.GetExtension(path);
if (!String.IsNullOrEmpty(extension))
{
if (FileTypes.Any(ft => ft.FileExtension.CompareNoCase(extension)))
return true;
}
return false;
}
public void SetViewActive(bool isActive)
{
((SpreadsheetView)view).ShowIcon = isActive;
}
public IDocumentView New(string fileName)
{
// Opens a new file correctly.
}
public IDocumentView Open(string path)
{
// Opens an Excel file correctly.
}
public IEnumerable<DocumentFileType> FileTypes
{
get
{
return new List<DocumentFileType>()
{
new DocumentFileType("CSV", ".csv" ),
new DocumentFileType("Excel", ".xls"),
new DocumentFileType("Excel10", ".xlsx")
};
}
}
}
where the implemented interface is
public interface IDocumentController
{
bool Handles(string path);
void SetViewActive(bool isActive);
IDocumentView New(string fileName);
IDocumentView Open(string path);
IEnumerable<DocumentFileType> FileTypes { get; }
}
Now the view ascociated with this controller is
public partial class SpreadsheetView : DockContent, ISpreadsheetView
{
private IDocumentController controller;
public SpreadsheetView()
{
InitializeComponent();
}
private void SpreadsheetView_Activated(object sender, EventArgs e)
{
controller.SetViewActive(true);
}
private void SpreadsheetView_Deactivate(object sender, EventArgs e)
{
controller.SetViewActive(false);
}
public void SetController(IDocumentController controller)
{
this.controller = controller;
Log.Trace("SpreadsheetView.SetController(): Controller set successfully");
}
public string DisplayName
{
get { return Text; }
set { Text = value; }
}
public WorkbookView WorkbookView
{
get { return workbookView; }
set { workbookView = value; }
}
...
}
Finally the view interfaces are
public interface ISpreadsheetView : IDocumentView
{
WorkbookView WorkbookView { get; set; }
}
and
public interface IDocumentView
{
void SetController(IDocumentController controller);
string DisplayName { get; set; }
bool StatusBarVisible { get; set; }
}
Now for my questions. In Seemann's book "Dependency Injection in .NET" he talks about the "Three Calls Pattern" and this is what I have attempted to implement in the above. The code works, the shell view displays and via the MVC pattern my controllers correctly open views etc. However, I am confused as the above definately has the flavour of the "Service Locator Anti-Pattern". In chapter 3 of Seemann's book he states
The COMPOSITION ROOT pattern describes where you should use a DI CONTAINER. However,
it doesn’t state how to use it. The REGISTER RESOLVE RELEASE pattern addresses
this question [...] A DI CONTAINER should be used in three successive
phases called Register, Resolve, and Release.
In its pure form, the REGISTER RESOLVE RELEASE pattern states that you should only
make a single method call in each phase. Krzysztof Kozimic calls this the Three Calls Pattern.
Configuring a DI CONTAINER in a single method call requires more explanation. The
reason that registration of components should happen in a single method call is
because you should regard configuration of a DI CONTAINER as a single, atomic action.
Once configuration is completed, the container should be regarded as read-only.
This sounds like the dredded "Service locator", why is this not deemed service location?
In order to adjust my code to instead use Contstructor Injection, I changed my entry code to
[STAThread]
static void Main()
{
var kernel = new StandardKernel();
kernel.Bind(t => t.FromThisAssembly()
.SelectAllClasses()
.BindAllInterfaces());
FileLogHandler fileLogHandler = new FileLogHandler(Utils.GetLogFilePath());
Log.LogHandler = fileLogHandler;
Log.Trace("Program.Main(): Logging initialized");
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(kernel.Get<ApplicationShellView>());
}
using Ninject.Extensions.Conventions, I then changed ApplicationShellController in order to correct my code to inject the IDocumentControllers via ctor injection:
public class ApplicationShellController
{
private IApplicationShellView shellView;
private IEnumerable<IDocumentController> controllers;
public ApplicationShellController(IApplicationShellView shellView, IEnumerable<IDocumentController> controllers)
{
this.shellView = shellView;
this.controllers = controllers;
Log.Trace("ApplicationShellController.Ctor(): Shell initialized successfully");
}
...
}
where
public class SpreadsheetController : IDocumentController
{
private ISpreadsheetView view;
public SpreadsheetController(ISpreadsheetView view)
{
this.view = view;
this.view.SetController(this);
}
...
}
but this leads to a circular dependency, how do I handle this?
Question Summary:
Why is my initial use of Ninject using "Thee Calls Pattern" and CompositionRoot.Resolve<T>() bad or different to the Service Locator Anti-Pattern?
How can I resolve the circular dependency issue above if I want to switch to pure ctor injection?
Thanks very much for your time.

At some point in the process, you have to use service location. However, the difference between DI and SL is that in SL, you are resolving your services at the point they are requested, whereas in DI you resolve them in some kind of factory (such as a controller factory) and then construct your objects and pass the reference in.
You should create some kind of infrastructure that dispatches your commands and uses a factory of some kind to locate the dependencies used by the created objects.
In this way, the rest of your code doesn't have dependency resolution, and you are following a DI pattern except at the construction point.

Property setter injection [Inject] Not working

I am trying to use property Setter injection method, in the FilterAttribute class
Below is my AttributeFilter
public class HasIfNoneMatchAttribute : ActionFilterAttribute
{
[Inject]
public ICorporationRepository _corporationRepository { set; private get; }
public override void OnActionExecuting(HttpActionContext actionContext)
{
var request = actionContext.Request;
ICollection<EntityTagHeaderValue> etagsFromClient = request.Headers.IfNoneMatch;
if (etagsFromClient.Count > 0)
{
EntityTagHeaderValue etag = new EntityTagHeaderValue(this._corporationRepository.GetETagForCorporationRequirement("param1", "param2", "param3"));
if (etagsFromClient.Contains(etag))
{
actionContext.Response = new HttpResponseMessage(HttpStatusCode.NotModified);
// SetCacheControl(context.Response);
}
}
base.OnActionExecuting(actionContext);
}}
}
I am already using constructor injection in the project. which works fine.
Below is part of my NinjectWebCommon.cs file
public static class NinjectWebCommon
{
private static readonly Bootstrapper bootstrapper = new Bootstrapper();
public static void Start()
{
DynamicModuleUtility.RegisterModule(typeof(OnePerRequestHttpModule));
DynamicModuleUtility.RegisterModule(typeof(NinjectHttpModule));
bootstrapper.Initialize(CreateKernel);
}
public static void Stop()
{
bootstrapper.ShutDown();
}
private static IKernel CreateKernel()
{
var kernel = new StandardKernel();
kernel.Bind<Func<IKernel>>().ToMethod(ctx => () => new Bootstrapper().Kernel);
kernel.Bind<IHttpModule>().To<HttpApplicationInitializationHttpModule>();
RegisterServices(kernel);
return kernel;
}
private static void RegisterServices(IKernel kernel)
{
kernel.Bind<ICorporationRepository>().To<CorporationRepository>();
}
Property is not getting injected, and I get the error -
System.NullReferenceException: Object reference not set to an instance of an object.
What am I missing?

How inject depedency to CompositeControl using Ninject

How to inject dependency into CompositeControl?
I tried the following approach - MyServerControl's Calculate is still null.
Thanks!
public class MyServerControl : CompositeControl
{
private TextBox TextBox1;
private TextBox TextBox2;
private Label Label1;
[Inject] // **** This is null ****
public ICalculate Calculate { get; set; }
protected override void CreateChildControls()
{
TextBox1 = new TextBox {ID = "TextBox1", Text = "1"};
Controls.Add(TextBox1);
TextBox2 = new TextBox {ID = "TextBox2", Text = "2"};
Controls.Add(TextBox2);
var button1 = new Button {ID = "Button1", Text = "Calculate"};
button1.Click += button1_Click;
Controls.Add(button1);
Label1 = new Label {ID = "Label1"};
Controls.Add(Label1);
}
private void button1_Click(object sender, EventArgs e)
{
int value1 = Int32.Parse(TextBox1.Text);
int value2 = Int32.Parse(TextBox2.Text);
Label1.Text = "Result:" + Calculate.Add(value1, value2);
}
}
public interface ICalculate
{
int Add(int x, int y);
}
public class Calculate : ICalculate
{
public int Add(int x, int y)
{
return x + y;
}
}
Default Ninject.Web.Common Bootstrapper from NuGet:
using System.Net.NetworkInformation;
[assembly: WebActivator.PreApplicationStartMethod(typeof(NinjectDemo.App_Start.NinjectWebCommon), "Start")]
[assembly: WebActivator.ApplicationShutdownMethodAttribute(typeof(NinjectDemo.App_Start.NinjectWebCommon), "Stop")]
namespace NinjectDemo.App_Start
{
using System;
using System.Web;
using Microsoft.Web.Infrastructure.DynamicModuleHelper;
using Ninject;
using Ninject.Web.Common;
public static class NinjectWebCommon
{
private static readonly Bootstrapper bootstrapper = new Bootstrapper();
/// <summary>
/// Starts the application
/// </summary>
public static void Start()
{
DynamicModuleUtility.RegisterModule(typeof(OnePerRequestHttpModule));
DynamicModuleUtility.RegisterModule(typeof(NinjectHttpModule));
bootstrapper.Initialize(CreateKernel);
}
/// <summary>
/// Stops the application.
/// </summary>
public static void Stop()
{
bootstrapper.ShutDown();
}
/// <summary>
/// Creates the kernel that will manage your application.
/// </summary>
/// <returns>The created kernel.</returns>
private static IKernel CreateKernel()
{
IKernel kernel = new StandardKernel();
kernel.Bind<Func<IKernel>>().ToMethod(ctx => () => new Bootstrapper().Kernel);
kernel.Bind<IHttpModule>().To<HttpApplicationInitializationHttpModule>();
RegisterServices(kernel);
return kernel;
}
/// <summary>
/// Load your modules or register your services here!
/// </summary>
/// <param name="kernel">The kernel.</param>
private static void RegisterServices(IKernel kernel)
{
kernel.Bind<ICalculate>().To<Calculate>().InSingletonScope();
}
}
}
Updated:
I'm not able to get instance to kernel in Page_Load. Am I missing something?
<my:MyServerControl ID="MyServerControl1" runat="server" />
public partial class Default : Page
{
[Inject]
public ICalculate _calculate { get; set; }
protected void Page_Load(object sender, EventArgs e)
{
kernel.Inject(MyServerControl1); // kernel is not available
}
}

I think you could just use the feature that satisfies dependencies on an existing object. In this particular case, in any context your control is used, you just call
kernel.Inject( myControl );
where myControl is an existing instance of your composite control. This has to be called from the code behind, somewhere in the pipeline where the instance is already created. Page_Load would most probably be fine.
Edit: there are numerous ways to be able to resolve anywhere in your application. You could for example have a global service locator. But since you are using the Bootstrapper, you should be able to resolvd your kernel anywhere
var kernel = (IKernel)Bootstrapper.Container;

Your Default page doesn't know about NinjectWebCommon class existence. It also cannot know about the kernel variable which is a NinjectWebCommon.CreateKernel() method's member. The simplest solution is the following:
public static class NinjectWebCommon
{
...
private static IKernel kernel;
public static IKernel CreateKernel()
{
if(kernel != null)
return kernel;
kernel = new StandardKernel();
kernel.Bind<Func<IKernel>>().ToMethod(ctx => () => new Bootstrapper().Kernel);
kernel.Bind<IHttpModule>().To<HttpApplicationInitializationHttpModule>();
RegisterServices(kernel);
return kernel;
}
...
}
public partial class Default : Page
{
[Inject]
public ICalculate _calculate { get; set; }
protected void Page_Load(object sender, EventArgs e)
{
NinjectWebCommon.CreateKernel().Inject(MyServerControl1);
}
}
The other way would be to use Ninject magic. Your application class would probably need to inherit from a class provided by Ninject. In MVC it's a NinjectHttpApplication class, which overrides the bootstrapper. Than you could probably go with Wiktor's answer.
Honestly I don't like that Ninject magic, as it sometimes doesn't work for me and than it's very hard to find out why. In my MVC application I ended up creating my own ConfrollerFactory, which injected the dependencies explicitly. It also may be a pain if you want to change your IOC container.

you need to register your Ioc config, see example:
public static void RegisterIoc(HttpConfiguration config)
{
var kernel = new StandardKernel(); // Ninject IoC
kernel.Bind<IMyService>().To<MyService>();
// Tell WebApi how to use our Ninject IoC
config.DependencyResolver = new NinjectDependencyResolver(kernel);
}
public class NinjectDependencyResolver : NinjectDependencyScope, IDependencyResolver
{
private IKernel kernel;
public NinjectDependencyResolver(IKernel kernel)
: base(kernel)
{
this.kernel = kernel;
}
public IDependencyScope BeginScope()
{
return new NinjectDependencyScope(kernel.BeginBlock());
}
}
public class NinjectDependencyScope : IDependencyScope
{
private IResolutionRoot resolver;
internal NinjectDependencyScope(IResolutionRoot resolver)
{
Contract.Assert(resolver != null);
this.resolver = resolver;
}
public void Dispose()
{
var disposable = resolver as IDisposable;
if (disposable != null)
disposable.Dispose();
resolver = null;
}
public object GetService(Type serviceType)
{
if (resolver == null)
throw new ObjectDisposedException("this", "This scope has already been disposed");
return resolver.TryGet(serviceType);
}
public IEnumerable<object> GetServices(Type serviceType)
{
if (resolver == null)
throw new ObjectDisposedException("this", "This scope has already been disposed");
return resolver.GetAll(serviceType);
}
}
Add this class in your App_start folder, and then write in Global.asax.cs:
// Tell WebApi to use our custom Ioc (Ninject)
IocConfig.RegisterIoc(GlobalConfiguration.Configuration);

Can I register my types in modules in Unity like I can in Autofac?

I am fairly familiar with Autofac and one feature that I really love about Autofac is the registering of modules. Does anyone know how I can do this with Unity? I'm having a hard time finding which terms to use in Google to come up with the unity equivalent if there is one.
public class Global : HttpApplication, IContainerProviderAccessor
{
private static IContainerProvider _containerProvider;
protected void Application_Start(object sender, EventArgs e)
{
var builder = new ContainerBuilder();
builder.RegisterModule(new MyWebModule());
_containerProvider = new ContainerProvider(builder.Build());
}
[...]
public IContainerProvider ContainerProvider
{
get { return _containerProvider; }
}
}
public class MyWebModule: Module
{
protected override void Load(ContainerBuilder builder)
{
builder.RegisterModule(new ApplicationModule());
builder.RegisterModule(new DomainModule());
}
}
public class ApplicationModule: Module
{
protected override void Load(ContainerBuilder builder)
{
builder.Register(c => new ProductPresenter(c.Resolve<IProductView>()))
.As<ProductPresenter>()
.ContainerScoped();
}
}

Actually, you can do trivially with Unity container extensions.
public class Global : HttpApplication, IContainerProviderAccessor
{
private static IContainerProvider _containerProvider;
protected void Application_Start(object sender, EventArgs e)
{
var container = new UnityContainer();
container.AddNewExtension<MyWebModule>();
_containerProvider = new ContainerProvider(container);
}
[...]
public IContainerProvider ContainerProvider
{
get { return _containerProvider; }
}
}
public class MyWebModule : UnityContainerExtension
{
protected override void Initialize()
{
Container.AddNewExtension<ApplicationModule>();
Container.AddNewExtension<DomainModule>();
}
}
public class ApplicationModule: UnityContainerExtension
{
protected override void Initialize()
{
Container.RegisterType<ProductPrensenter>(
new ContainerControlledLifetimeManager(),
new InjectionFactory(c => new ProductPresenter(c.Resolve<IProductView>())));
}
}

You can't. Just use Autofac or Windsor. You will find there's a lot missing in Unity and what's there works in unexpected ways. It's just not worth your time.