如何删除用作侦听器的lambda表达式/方法句柄？ [英] How do I remove lambda expressions/method handles that are used as listeners?

问题描述

Java 8引入了 lambda表达式，这是一件好事。但现在考虑重写这段代码：

Java 8 has introduced lambda expressions, which is a great thing. But now consider rewriting this code:

class B implements PropertyChangeListener {
    void listenToA(A a) {
        a.addPropertyChangeListener(this);
    }

    void propertyChange(PropertyChangeEvent evt) {
        switch(evt.getPropertyName()) {
            case "Property1":
                doSomething();
                break;
            case "Property2":
                doSomethingElse();                case "Property1":
                doSomething;
                break;

                break;
    }

    void doSomething() { }
    void doSomethingElse() { }
}

class A {
    final PropertyChangeSupport pcs = new PropertyChangeSupport(this);

    void addPropertyChangeListener(PropertyChangeListener listener) {
        pcs.addPropertyChangeListener(listener);
    }

    void removePropertyChangeListener(PropertyChangeListener listener) {
        pcs.removePropertyChangeListener(listener);
    }
}

使用lambda表达式和方法引用，它已不复存在必须要 B 实施 PropertyChangeListner 我们可以写

With lambda expressions and method references, it is no more necessary to have B implement PropertyChangeListner as we can write

class B {
    void listenToA(A a) {
        // using method reference
        a.addPropertyChangeListener("Property1", this::doSomething);
        // using lambda expression
        a.addPropertyChangeListener("Property2", e -> doSomethingElse());
    }

    void doSomething(PropertyChangeEvent evt) { }
    void doSomethingElse() { }
}

class A {
    final PropertyChangeSupport pcs = new PropertyChangeSupport(this);

    void addPropertyChangeListener(String name, PropertyChangeListener listener) {
        pcs.addPropertyChangeListener(name, listener);
    }

    void removePropertyChangeListener(String name, PropertyChangeListener listener) {
        pcs.removePropertyChangeListener(name, listener);
    }
}

我认为新代码不仅更短，而且还更清洁，更容易理解。但在阅读此处后的答案后（这个，但我认为问题和答案更清晰），我看不到实现一个名为 stopListening（）的方法的方法，它会再次删除监听器。

I think the new code is not only shorter but also cleaner and easier to understand. But after reading the answers given here (duplicate of this one, but I think question and answer are more crisp), I can see no way to implement a method called stopListening() which would remove the listeners again.

我确定我是不是第一个偶然发现的人。那么有没有人找到一个关于如何使用方法句柄的很好的解决方案，如本例所示，并且仍然可以在以后再次删除监听器？

I am sure that I am not the first one to stumble on this. So has anyone found a nice solution on how to use method handles as shown in this example and still being able to remove the listeners again later?

UPDATE

这很快。基于Mike Naklis和Hovercraft Full Of Eels的答案，我最终得到了这个：

That was fast. Building on the answers by Mike Naklis and Hovercraft Full Of Eels, I ended up with this:

class B {
    void listenToA(A a) {
        a.addPropertyChangeListener("Property1", doSomething);
        a.addPropertyChangeListener("Property2", doSomethingElse);
    }

    final PropertyChangeListener doSomething = evt -> {};
    final PropertyChangeListener doSomethingElse = evt -> {};
}

推荐答案

您可以将听众声明为如下：

You can declare your listeners as follows:

private final PropertyChangeListener myProperty1Listener = this::doSomething;
private final PropertyChangeListener myProperty2Listener = e -> doSomethingElse());

然后，你可以添加你的听众：

then, you can add your listeners:

// using method reference
a.addPropertyChangeListener( "Property1", myProperty1Listener );
// using lambda expression
a.addPropertyChangeListener( "Property2", myProperty2Listener );

你可以删除它们：

a.removePropertyChangeListener( "Property1", myProperty1Listener );
a.removePropertyChangeListener( "Property2", myProperty2Listener );

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