如何以干净的方式解析处理程序

Question

我试图找到一种简单的方法来解决我的处理程序。解决方案是"handling different types of messages"。但是我找到的每个解决方案，例如 this idea，我都坚持解析处理程序，因为我的处理程序有一个构造函数，它对其他接口有一些依赖性。

例如，如果我遵循上述想法，我的 OrderMessageHandler 是

public class OrderMessageHandler
{
    private readonly IInterface _interface;
    public OrderMessageHandler(IInterface interface) {_inteface=interface}

    bool HandleMessage( IMessage msg ) {
        if ( !(msg is OrderMessage)) return false;
        return true; 
    }
}

然而 IInterface 有其他依赖关系，我不能简单地解决它。我想知道是否有人有比下面这个更好的主意 class？

public class MessageProcessor {
    private List<IMessageHandler> handlers;

    public MessageProcessor() {
       handlers = new List<IMessageHandler>();
       handlers.add(new SomeOtherMessageHandler());
       handlers.add(new OrderMessageHandler());
    }

    public void ProcessMessage( IMessage msg ) {
       bool messageWasHandled
       foreach( IMessageHandler handler in handlers ) {
           if ( handler.HandleMessage(msg) ) {
               messageWasHandled = true;
               break;
           }
       }

       if ( !messageWasHandled ) {
          // Do some default processing, throw error, whatever.
       }
    }
}

Answer 1

遵循Explicit Dependencies Principle，您可以确保所有必要的依赖项都注入其中。

public class MessageProcessor {
    private List<IMessageHandler> handlers;

    public MessageProcessor(IEnumerable<IMessageHandler> handlers) {
        this.handlers = new List<IMessageHandler>(handlers);
        //removed
        //handlers.add(new SomeOtherMessageHandler()); 
        //handlers.add(new OrderMessageHandler());
    }

    public void ProcessMessage( IMessage msg ) {
       bool messageWasHandled
       foreach( IMessageHandler handler in handlers ) {
           if ( handler.HandleMessage(msg) ) {
               messageWasHandled = true;
               break;
           }
       }

       if ( !messageWasHandled ) {
          // Do some default processing, throw error, whatever.
       }
    }
}

如果使用 DI 容器，请确保注册所有相关方

伪代码：

container.Register<IInterface, Implementation>();
container.Register<IMessageHandler, SomeOtherMessageHandler>();
container.Register<IMessageHandler, OrderMessageHandler>();
container.Register<MessageProcessor>();

这样容器就知道如何在解析所需类型时构建对象图

MessageProcessor processor = container.Resolve<MessageProcessor>();

processor.ProcessMessage(...);

//...

如果使用 Pure DI 这仍然允许在需要的地方正确创建和注入所有涉及的类型。

IInterface dependency = new Implementation();
List<IMessageHandler> handlers = new List<IMessageHandler>();
handlers.Add(new SomeOtherMessageHandler()); 
handlers.Add(new OrderMessageHandler(dependency));
MessageProcessor processor = new MessageProcessor(handlers);

processor.ProcessMessage(...);

//...

如何以干净的方式解析处理程序

How to resolve handler in a clean way

c#

dependency-injection

dependency-resolver