Let's say I would like to inject an implementation of this interface:
interface IService { ... }
implemented as:
class MyService : IService
{
public MyService(string s) { }
}
in an instance of this class:
class Target
{
[Inject]
public IService { private get; set; }
}
I do the injection by calling kernel.Inject(new Target()), but what if I would like to specify the parameter s of the constructor depending on some context when calling Inject?
Is there a way to achieve such context-dependant service initialization at injection?
Thanks!
In most cases you should not use Field Injection, it should be
used only in rare cases of circular dependencies.
You should only use the kernel once at the start of your
application and never again.
Example Code:
interface IService { ... }
class Service : IService
{
public Service(string s) { ... }
}
interface ITarget { ... }
class Target : ITarget
{
private IService _service;
public Target(IServiceFactory serviceFactory, string s)
{
_service = serviceFactory.Create(s);
}
}
interface ITargetFactory
{
ITarget Create(string s);
}
interface IServiceFactory
{
IService Create(string s);
}
class NinjectBindModule : NinjectModule
{
public NinjectBindModule()
{
Bind<ITarget>().To<Target>();
Bind<IService>().To<Service>();
Bind<ITargetFactory>().ToFactory().InSingletonScope();
Bind<IServiceFactory>().ToFactory().InSingletonScope();
}
}
Usage:
public class Program
{
public static void Main(string[] args)
{
IKernel kernel = new StandardKernel(new NinjectBindModule());
var targetFactory = kernel.Get<ITargetFactory>();
var target = targetFactory.Create("myString");
target.DoStuff();
}
}
Simply done using parameters...
kernel.Inject(new Target(), new ConstructorArgument("s", "someString", true));
Related
Say i have a code as follows
interface Interface1
{
void method1();
}
interface Interface2
{
void method2();
}
class ClassWithInterfaces : Interface1,Interface2
{
void method1(){}
void method2(){}
}
Now in my "manager" class i implement this as follows :
public OtherClass
{
Interface1 interface1;
Interface2 interface2;
public void someMethod()
{
ClassWithInterfaces classWithInterfaces = new ClassWithInterfaces();
interface1 = classWithInterfaces;
interface2 = classWithInterfaces
}
}
I don't feel that this is the right way to do it hovewer i can't come up with other solutions i can't use Dependency Injection Frameworks in my project if you ask about that. Can you tell me wheter apart from DI there is a better way of doing that?
Hello and welcome to Stack Overflow :-)
You don't have to use a framework in order to do DI. In fact, there are some languages that make it impossible to use a framework for DI - e.g., C++.
Any way, in your case, the proper way to do DI is like this:
interface Interface1
{
void method1();
}
interface Interface2
{
void method2();
}
interface Interface3 : Interface1, Interface2
{
void method1();
void method2();
}
class ClassWithInterfaces : Interface3
{
void method1(){}
void method2(){}
}
public OtherClass
{
Interface3 m_interface3;
OtherClass(Interface3 interface3)
{
m_interface3 = interface3;
}
public void someMethod()
{
m_interface3.method1();
m_interface3.method2();
}
}
// And now the usage:
public main()
{
ClassWithInterfaces classWithInterfaces = new ClassWithInterfaces();
OtherClass otherClass = new OtherClass(classWithInterfaces);
}
I am getting the following error whenever I try to inject one of my service's dependency into the MVC controller:
Error activating IFeedService No matching bindings are available, and the type is not self-bindable.
Activation path:
2) Injection of dependency IFeedService into parameter svc of constructor of type FeedController
1) Request for FeedController
Suggestions:
1) Ensure that you have defined a binding for IFeedService.
2) If the binding was defined in a module, ensure that the module has been loaded into the kernel.
3) Ensure you have not accidentally created more than one kernel.
4) If you are using constructor arguments, ensure that the parameter name matches the constructors parameter name.
5) If you are using automatic module loading, ensure the search path and filters are correct.
======================================================================
Here's how my code looks like:
ObjectFactory.cs
private static void RegisterServices(IKernel kernel)
{
// Contexts
kernel.Bind<IEntityObjectContext>().To<Entities>();
kernel.Bind<IAzureObjectContext>().To<AzureTableObjectContext>();
// Repositories
kernel.Bind<IEFRepository>().To<EFRepository>();
kernel.Bind<IAzureRepository>().To<AzureRepository>();
// Services
kernel.Bind<IFeedService>().To<FeedService>();
}
IEFRepository.cs
public interface IEFRepository : IDisposable
{
void SetContext(IEntityObjectContext context);
IQueryable<T> GetAll<T>() where T : class;
}
EFRepository.cs
public class EFRepository : IEFRepository
{
internal IEntityObjectContext context;
private Dictionary<Type, object> objectSets;
public EFRepository(IEntityObjectContext context)
{
this.context = context;
objectSets = new Dictionary<Type, object>();
}
public void SetContext(IEntityObjectContext context)
{
this.context = context;
}
}
IFeedService.cs
public interface IFeedService : IDisposable
{
IQueryable<FeedItem> GetPosts();
}
FeedService.cs
public class FeedService : IFeedService
{
private IEntityObjectContext _context;
private readonly IEFRepository _repo;
public FeedService(IEntityObjectContext context,
IEFRepository repo)
{
_context = context;
_repo = repo;
_repo.SetContext(_context);
}
public IQueryable<FeedItem> GetPosts()
{
using (_repo)
{
return _repo.GetAll<FeedItem>().Take(10);
}
}
}
FeedController.cs
public class FeedController : Controller
{
private readonly IFeedService _svc;
public FeedController(IFeedService svc)
{
_svc = svc;
}
}
As you can see, there are some nested dependency there in action. Not sure though, what needs to be added/removed for this bit to work.
Note: The error is thrown whenever I request the Feed/FetchFeed path. I also tried to comment out the FeedService's constructor portion to see if the nested dependencies are creating any problem, but again same error was thrown.
EDIT 1:
Rest of the code for the ObjectFactory.cs
class ObjectFactory
{
static ObjectFactory()
{
RegisterServices(kernel);
}
static IKernel kernel = new StandardKernel();
public static T GetInstance<T>()
{
return kernel.Get<T>();
}
private static void RegisterServices(IKernel kernel)
{
//...
}
}
EDIT 2:
I even tried to write a fairly basic service, but still the same error. Here's what I tried with:
public interface ITest
{
void CheckItOut();
}
public class Test : ITest
{
public void CheckItOut()
{
}
}
ObjectFactory.cs
kernel.Bind<ITest>().To<Test>();
Ninject doesn't seem to correctly use WhenInjectedInto contstraint while also using Lazy<T>. Check the following example. The OnLandAttack and the OnLandAttackLazy should each be using the Samurai instance. But the Lazy<T> version ends up with the SpecialNinja instance. I'm guessing it's because it's not actually initialized in the contructor? But the type should still be correctly registered I would think. Am I missing something? FYI, this is using Ninject 3.2.2 and the Ninject.Extensions.Factory extension 3.2.1
class Program
{
static void Main(string[] args)
{
var kernel = new StandardKernel();
kernel.Load(new WarriorModule());
var amphibious = kernel.Get<IAttack>("amphibious");
amphibious.Execute();
var onLand = kernel.Get<IAttack>("onLand");
onLand.Execute();
var onLandLazy = kernel.Get<IAttack>("onLandLazy");
onLandLazy.Execute();
Console.ReadKey();
}
}
public class WarriorModule : NinjectModule
{
public override void Load()
{
Bind<IWarrior>().To<Samurai>().WhenInjectedInto<OnLandAttack>();
Bind<IWarrior>().To<Samurai>().WhenInjectedInto<OnLandAttackLazy>();
Bind<IWarrior>().To<SpecialNinja>(); // <-- for everything else
Bind<IAttack>().To<AmphibiousAttack>().Named("amphibious");
Bind<IAttack>().To<OnLandAttack>().Named("onLand");
Bind<IAttack>().To<OnLandAttackLazy>().Named("onLandLazy");
}
}
public interface IWarrior
{
void Attack();
}
public class Samurai : IWarrior
{
public void Attack()
{
Console.WriteLine("\tSamurai Attack");
}
}
public class SpecialNinja : IWarrior
{
public void Attack()
{
Console.WriteLine("\tSpecial Ninja Attack");
}
}
public interface IAttack
{
void Execute();
}
public class OnLandAttack : IAttack
{
private readonly IWarrior warrior;
public OnLandAttack(IWarrior warrior)
{
this.warrior = warrior;
}
public void Execute()
{
Console.WriteLine("Begin OnLand attack");
this.warrior.Attack();
}
}
public class OnLandAttackLazy : IAttack
{
private readonly Lazy<IWarrior> warrior;
public OnLandAttackLazy(Lazy<IWarrior> warrior)
{
this.warrior = warrior;
}
public void Execute()
{
Console.WriteLine("Begin OnLandLazy attack");
this.warrior.Value.Attack();
}
}
public class AmphibiousAttack : IAttack
{
private readonly IWarrior warrior;
public AmphibiousAttack(IWarrior warrior)
{
this.warrior = warrior;
}
public void Execute()
{
Console.WriteLine("Begin Amphibious attack");
this.warrior.Attack();
}
}
A bit of history first. I created a EF Code First Library that contains POCO Objects as my Models, a generic DataProvider that inherits from DbContext, generic Repostory that implements the generic DataProvider, and a generic Service that implements the repository. I have used this library successfully in WPF (MVVM), ASP.Net, Window Forms, and ASP MVC applications.
For this discussion I will reference the Company Model
From the top down, I create a Service class called CompanyService that inherits from a base Service Class. The CompanyService class contains all of the business logic for the Company Model. This class uses the Repository class to perform the CRUD operations. The Repository then encapsulates all the DataProvider class operations.
I have done some research on using EF with WCFDataService, but I can't get my head around how to implement my library with it, particulary when it comes to overriding the CreateDataSource() Method.
It may be that I should just use a WCF Service instead, maybe I'm not understanding the purpose of the WCFDataService.
I have listed partial code for the classes involved:
public class CompanyService : ServiceBase<Company> ,ICompanyService
{
public Company GetCompanyByFolderId(string eFolderId)
{
return (Company)GetModelByFolderId(eFolderId);
}
}
public abstract class ServiceBase<TModel> : IService<TModel> where TModel : class, IModel
{
private IDataProvider _dataProvider;
public IDataProvider DataProvider
{
get
{
if (_dataProvider == null)
{
string connectionStringName = Properties.Settings.Default.DataProvider;
bool enableLazyLoading = true;
_dataProvider = new DataProvider(connectionStringName, enableLazyLoading);
}
return _dataProvider;
}
set
{
_dataProvider = value;
}
}
private IRepository<TModel> _repository;
public IRepository<TModel> Repository
{
get
{
if (_repository == null)
{
_repository = new Repository<TModel>(DataProvider);
}
return _repository;
}
set
{
_repository = value;
}
}
public TModel GetModelByFolderId(String folderId)
{
return GetTable().FirstOrDefault(o => o.EFolderid == folderId);
}
public virtual IQueryable<TModel> GetTable()
{
return Repository.GetTable();
}
}
public class Repository<TModel> : IRepository<TModel> where TModel : class, IModel
{
private IDataProvider _dataProvider;
public Repository(IDataProvider dataProvider)
{
_dataProvider = dataProvider;
}
private IDbSet<TModel> DbSet
{
get
{
return _dataProvider.Set<TModel>();
}
}
public IQueryable<TModel> GetTable()
{
return _dataProvider.GetTable<TModel>();
}
}
public class DataProvider : DbContext, IDataProvider
{
public DataProvider()
{
}
public DataProvider(string connectionStringName, bool enableLazyLoading = true)
: base(connectionStringName)
{
Configuration.LazyLoadingEnabled = enableLazyLoading;
//Configuration.ProxyCreationEnabled = false;
}
public new IDbSet<TModel> Set<TModel>() where TModel : class
{
return base.Set<TModel>();
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Configurations.Add(new CompanyMapping());
base.OnModelCreating(modelBuilder);
}
public IQueryable<TModel> GetTable<TModel>() where TModel : class
{
return Set<TModel>().AsQueryable();
}
}
Then my Test looks something like this:
[TestClass()]
public class CompanyServiceTest
{
[TestMethod()]
public void GetCompanies()
{
CompanyService target = new CompanyService();
IQueryable<Company> companies = target.GetTable();
Assert.IsNotNull(companies);
}
[TestMethod()]
public void GetCompanyByFolderId()
{
CompanyService target = new CompanyService();
Company company = target.GetCompanyByFolderId("0000000000000000000000000172403");
Assert.IsNotNull(company);
}
}
Is it possible to change the default object scope in Ninject 2.2? If so, how is it done?
As far as I can tell you could override AddBinding() on the BindingRoot (StandardKernel or NinjectModule) and modify the ScopeCallback property on the binding object.
public class CustomScopeKernel : StandardKernel
{
public CustomScopeKernel(params INinjectModule[] modules)
: base(modules)
{
}
public CustomScopeKernel(
INinjectSettings settings, params INinjectModule[] modules)
: base(settings, modules)
{
}
public override void AddBinding(IBinding binding)
{
// Set whatever scope you would like to have as the default.
binding.ScopeCallback = StandardScopeCallbacks.Singleton;
base.AddBinding(binding);
}
}
This test should now pass (using xUnit.net)
public class DefaultScopedService { }
[Fact]
public void Should_be_able_to_change_default_scope_by_overriding_add_binding()
{
var kernel = new CustomScopeKernel();
kernel.Bind<DefaultScopedService>().ToSelf();
var binding = kernel.GetBindings(typeof(DefaultScopedService)).First();
binding.ScopeCallback.ShouldBe(StandardScopeCallbacks.Singleton);
}
The CustomScopeKernel will also work with Ninject modules.
public class ServiceModule : NinjectModule
{
public override void Load()
{
Bind<DefaultScopedService>().ToSelf();
}
}
[Fact]
public void Should_be_able_to_change_default_scope_for_modules()
{
var module = new ServiceModule();
var kernel = new CustomScopeKernel(module);
var binding = kernel.GetBindings(typeof(DefaultScopedService)).First();
binding.ScopeCallback.ShouldBe(StandardScopeCallbacks.Singleton);
}