使用參數調用對象的非靜態方法引用

Question

我正在創建一個事件處理框架，並希望執行以下操作：

// E: event listener interface, T: event class
class EventManager<E, T> {

    ArrayList<E> listeners = new ArrayList<E>();

    // `method` is some sort of reference to the method to call on each listener. There is no `MethodReference` type, I just put it there as I'm not sure what type should be in its place
    protected void notifyListeners(MethodReference method, T eventObj) {
        for (E listener : listeners) // call `method` from `listener` with `eventObj` as an argument
   }
}

class SpecialisedEventManager extends EventManager<SomeListener, SomeEvent> {

    // Some method that would want to notify the listeners
    public void foo() {
        ...
        // I would like onEvent() to be called from each listener with new SomeEvent() as the argument
        notifyListeners(SomeListener::onEvent, new SomeEvent());
        ...
    }

    // Some other method that would want to notify the listeners
    public void bar() {
        ...
        notifyListeners(SomeListener::onOtherEvent, new SomeEvent());
        ...
    }

}

interface SomeListener {
    public void onEvent(SomeEvent event);
    public void onOtherEvent(SomeEvent event);
}

但我不確定如何引用onEvent()和onOtherEvent()方法，以便使用適當的參數從每個偵聽器對象調用它們。 有任何想法嗎？

Answer 1

方法引用只是實現功能接口的一種方式，因此您必須自己定義適當的接口或搜索預定義的類型以進行匹配。

由於您的偵聽器方法使用目標偵聽器實例和事件對象，並且不返回值，因此BiConsumer是一種合適的類型：

protected void notifyListeners(BiConsumer<E,T> method, T eventObj) {
    for(E listener: listeners)
        method.accept(listener, eventObj);
}

方法引用SomeListener::onEvent和SomeListener::onOtherEvent的形式為“引用任意對象的實例方法” ，其中調用者提供目標實例來調用方法，類似於lambda表達式(l,e) -> l.onEvent(e)和(l,e) -> l.onOtherEvent(e) ，這就是目標實例成為第一個功能參數的原因。