在Ninject中重新绑定通用接口

Question

I have several projects referencing a package containing generic interface

public interface IHandler<T> where T : class
{
    void Handle(T data);
}

These projects contain IHandler<> implementations and Ninject modules with bindings from interface to implementations.

I want to create decorator for all IHandler<> implementations

public class HandlerDecorator<T> : IHandler<T> where T : class
{
    private readonly IHandler<T> decorated;

    public HandlerDecorator(IHandler<T> decorated)
    {
        this.decorated = decorated;
    }

    public void Handle(T data)
    {
        // some logic 
    }
}

and decorate all registered bindings of IHandler<> automatically. Eg if there exists binding of IHandler<string> and StringHandler then target should be changed to new HandlerDecorator<string>(stringHandlerInstance) .

Is it possible in Ninject? Or I should rewrite all Ninject modules code?

Answer 1

As you can not access any meaningful binding information once the bindings are created, there is no direct way to accomplish this. You could, however, use Ninject.Extensions.Conventions to search for all IHandler<T> implementations and bind / re-bind them with the decorator. In Ninject, using a decorator requires a binding for the decorator and one for the decorated implementation. In case you always use the same decorator, it can be simplified by using a generic binding for the decorator. This would be:

kernel.Bind(typeof(IHandler<>)).To(typeof(HandlerDecorator));

(Or using Rebind instead of Bind - as needed).

And the binding created by using the conventions extension should equal to:

kernel.Bind<IHandler<string>>()
      .To<StringHandler>()
      .WhenInjectedInto<HandlerDecorator<string>>();

This is achieved by doing something along the lines of:

kernel.Bind( x => x
   .FromThisAssembly()
   .SelectAllClasses()
   .InheritedFrom(typeof(IHandler))
   .Excluding(typeof(HandlerDecorator<>))
   .BindDefaultInterface()
   .Configure(b => b.WhenInjectedInto(typeof(HandlerDecorator<>)));