在Java中实现适当的C#事件(非委托) [英] Implementing a proper C# event (not delegate) in java

问题描述

此 SO答案以及同一问题中的其他帖子中已经提到，可以使用接口实现C#委托或Java FuncationInterfaces.

As already mentioned in this SO answer and the other posts in the same question, C# delegates can be implemented using interfaces or Java FuncationInterfaces.

但是，我希望在Java中实现适当的事件模型，而不是委托模型.有关两者的区别的简要介绍，请参见此.尤其是第一条评论.

However I am looking to implement a proper event model and not a delegate model in Java. For a brief on the difference of the two, please see this. Especially the first comment.

以下是我到目前为止尝试过的内容:

Below is what I have tried so far:

Event.java

Event.java

public class Event {
    public interface EventHandler{
        void invoke();
    }

    private Set<EventHandler> mEventHandlers = new HashSet<>();

    public void add(EventHandler eventHandler){
        mEventHandlers.add(eventHandler);
    }

    public void remove(EventHandler eventHandler){
        mEventHandlers.remove(eventHandler);
    }

    public void invoke(){
        for(EventHandler eventHandler : mEventHandlers){
            if(eventHandler!=null) {
                eventHandler.invoke();
            }
        }
    }
}

EventPubisher.java

EventPubisher.java

public class EventPublisher {

    public Event ValueUpdatedEvent;

    public void UpdateValue(){
        ValueUpdatedEvent.invoke();
    }
}

EventConsumer.java

EventConsumer.java

public class EventConsumer {
    EventPublisher ep = new EventPublisher();

    public EventConsumer(){
        ep.ValueUpdatedEvent.add(this::ValueUpdatedEventHandler);
    }

    private void ValueUpdatedEventHandler(){
        // do stuff
    }
}

这种设计的问题是我也可以编写如下代码:

The problem with this design is that I can write code like below as well:

public class EventConsumer {
.....
    private void abuse(){
         ep.ValueUpdatedEvent.invoke();
    }
}

这尤其是事件所限制的.该事件仅应从声明类中引发，而不应从外部引发.

And this is particularly what events restrict. The event should be raised only from the declaring class and not from outside.

推荐答案

如@Jon Skeet在评论中所述，更改以下代码符合我的要求:

As mentioned by @Jon Skeet in the comments, changing the code as below meets my requirement:

EventPubisher.java

EventPubisher.java

public class EventPublisher {

    private final Event ValueUpdatedEvent = new Event();

    public void addEventHandler(Event.EventHandler eventHandler){
        ValueUpdatedEvent.add(eventHandler);
    }

    public void removeEventHandler(Event.EventHandler eventHandler){
        ValueUpdatedEvent.remove(eventHandler);
    }

    public void UpdateValue(){
        ValueUpdatedEvent.invoke();
    }
}

EventConsumer.java

EventConsumer.java

public class EventConsumer {
.....
    private void abuse(){
        // ep.ValueUpdatedEvent.invoke(); //Compilation error
    }
}

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