问题
This question is not specifically related to Ninject. It's more of a general coding question, but I'm posting it here in case there might be a better way entirely of handling the issue in Ninject, than what I am trying to do.
I would like to know whether it is possible to access the Ninject Standard Kernel globally, from its instance in Global.asax.
Here is the code:
public class MvcApplication : NinjectHttpApplication
{
protected override void OnApplicationStarted()
{
base.OnApplicationStarted();
// MVC global registration, routing and filtering code goes here...
}
protected override IKernel CreateKernel()
{
return Container;
}
private static IKernel Container
{
get
{
IKernel kernel = new StandardKernel();
kernel.Load(new ServiceModule(), new RepositoryModule());
return kernel;
}
}
}
If I have some classes, for example, facade classes that do not interface with the controllers, where I would like to begin a dependency chain, my understanding is I should use:
_className = kernel.Get<IClassName>();
However, the only way I know of to do this is to create a new instance of the Ninject Standard kernel, but if I understand correctly, is is not a good idea to create a new instance of the Ninject kernel, because that is basically creating a second kernel.
So, is it possible to access the existing Kernel that was instantiated in Global.asax at Application Start, from anywhere in my application, or is there a better way entirely to do this?
Regards,
Fred Chateau
回答1:
The most simple way (IMO):
_className = (IClassName)System.Web.Mvc.DependencyResolver.Current.GetService(typeof(IClassName));
回答2:
Newer version of Ninject has this method if used with System.Web.MVC:
var obj = DependencyResolver.Current.GetService<IClassName>();
Unless you need to manipulate DI bindings on the fly, but instantiating a StandardKernel is a little heavy.
IKernel kernel = new StandardKernel();
var obj = DependencyResolver.Current.GetService<IClassName>();
回答3:
I managed to get the Service Locator working, and it appears to be working quite well. When a request enters the application through an MVC Controller Action Method, Ninject functions in the normal way provided by Ninject.Mvc.Extensions. It injects instance classes through the controller constructor. When a request enters the application in any other way, I call the Service Locator to supply the instance classes in that classes constructor.
Here's the code:
First, a reference to Microsoft.Practices.ServiceLocation
And the following Ninject adapter class.
public class NinjectServiceLocator : ServiceLocatorImplBase
{
public IKernel Kernel { get; private set; }
public NinjectServiceLocator(IKernel kernel)
{
Kernel = kernel;
}
protected override object DoGetInstance(Type serviceType, string key)
{
return Kernel.Get(serviceType, key);
}
protected override IEnumerable<object> DoGetAllInstances(Type serviceType)
{
return Kernel.GetAll(serviceType);
}
}
And in Global.asax
public class MvcApplication : NinjectHttpApplication
{
private static IKernel _kernel;
protected override IKernel CreateKernel()
{
return Container;
}
private static IKernel Container
{
get
{
if (_kernel == null)
{
_kernel = new StandardKernel();
_kernel.Load(new ServiceModule(), new RepositoryModule());
ServiceLocator.SetLocatorProvider(() => new NinjectServiceLocator(_kernel));
}
return _kernel;
}
}
}
Note this code requires the use of Ninject.Mvc.Extensions, which provides dependency resolver fallback to the default controller. Otherwise, a custom dependency resolver may be required.
This appears to resolve all my concerns. It creates the instance classes, resolves the entire object graph, and works from anywhere I need it to work. And, as far as I can tell, there is only one Ninject Standard Kernel per application.
I know using the Service Locator pattern is frowned upon, but I imagine using more than one Ninject kernel would be frowned upon even worse.
Fred Chateau
回答4:
It sounds like you're needing more of a Factory pattern implementation of Ninject. You could migrate the Kernel from the Global.asax to a Factory class which could be interacted with by the rest of your application.
Alternatively if you have a situation where a parameter specified at runtime is to determine the interface bindings you could wrap the service. This is a hybrid setup of DI and ServiceLocater, but the ServiceLocater only occurs at service level instantiation, all other layers are coded normally in a DI/IOC pattern.
MyService : IService1
{
public void DoSomething(MyCustomParameter parameter)
{
//Builds the Kernel using the supplied parameter
//We've in our resolver bound IService1 To MyActualService
var trueService = kernel.Get<IService1>();
return trueService.DoSomething(parameter);
}
}
MyActualService : IService1
{
public void DoSomething()
{
//Do the Actual work
}
}
来源:https://stackoverflow.com/questions/15338162/accessing-the-ninject-kernel-globally