将基于IUnityContainer的泛型C# Mediator类重构为Ninject实现

疑问解答 #

• 是否应使用Ninject的StandardKernel替换IUnityContainer？
  是的，StandardKernel是Ninject的核心容器实现，对应Unity的IUnityContainer，用来管理依赖的注册与实例解析。
• 是否需要使用Ninject的Bind方法替代Unity的Resolve方法？
  不是。Bind是用来注册依赖关系的（对应Unity的Register系列方法），而Resolve是从容器获取实例的操作，Ninject用Get方法实现相同功能，和Unity的Resolve作用一致。你需要在应用启动时用Bind注册所有Handler，再在Mediator里用Get获取实例。

重构后的 Mediator.cs（Ninject 实现） #

using Ninject;

public sealed class Mediator : IMediator
{
    private readonly IKernel _kernel;

    public Mediator(IKernel kernel)
    {
        _kernel = kernel;
    }

    public TResponse Request<TResponse>(IQuery<TResponse> query)
    {
        var handlerType = typeof(IQueryHandler<,>).MakeGenericType(query.GetType(), typeof(TResponse));
        dynamic handler = _kernel.Get(handlerType); // Ninject用Get替代Unity的Resolve

        return handler.Handle((dynamic)query);
    }

    public TResult Send<TResult>(ICommand<TResult> command)
    {
        var handlerType = typeof(ICommandHandler<,>).MakeGenericType(command.GetType(), typeof(TResult));
        dynamic handler = _kernel.Get(handlerType);

        return handler.Handle((dynamic)command);
    }
}

依赖注册示例 #

应用初始化时，需要用Ninject注册所有QueryHandler和CommandHandler，示例如下：

var kernel = new StandardKernel();

// 单个Handler注册
kernel.Bind<IQueryHandler<GetUserQuery, UserDto>>().To<GetUserQueryHandler>();
kernel.Bind<ICommandHandler<CreateUserCommand, Guid>>().To<CreateUserCommandHandler>();

// 批量注册（需安装Ninject.Extensions.Conventions包）
kernel.Bind(x => x
    .FromAssemblyContaining<GetUserQueryHandler>()
    .SelectAllClasses()
    .InheritedFrom(typeof(IQueryHandler<,>))
    .BindAllInterfaces());

// 注册Mediator
kernel.Bind<IMediator>().To<Mediator>();

原接口定义 #

IMediator.cs #

public interface IMediator
{
    TResponse Request<TResponse>(IQuery<TResponse> query);
    TResult Send<TResult>(ICommand<TResult> command);
}

IQuery.cs #

public interface IQuery<out TResponse> { }

IQueryHandler.cs #

public interface IQueryHandler<in TQuery, out TResponse> where TQuery : IQuery<TResponse>
{
    TResponse Handle(TQuery query);
}

ICommand.cs #

public interface ICommand<out TResult> { }
public interface ICommand { }

ICommandHandler.cs #

public interface ICommandHandler<in TCommand, out TResult> where TCommand : ICommand<TResult>
{
    TResult Handle(TCommand command);
}

public interface ICommandHandler<in TCommand> where TCommand : ICommand
{
    void Handle(TCommand command);
}

内容的提问来源于stack exchange，提问作者ADH