[英]Passing generic event to Guava EventBus?
I've become very fond of Google Gauva's EventBus, so much that I want to include it in one of my Swing GridBagBuilder API's. 我非常喜欢谷歌Gauva的EventBus,以至于我想把它包含在我的一个Swing GridBagBuilder API中。 The goal is to take a Swing component and do something with it in an arbitrary event, and subscribe this to an EventBus.
目标是使用Swing组件并在任意事件中对其执行某些操作,并将其订阅到EventBus。 The problem is I think the reflection operations done by the EventBus are not liking my generics for any arbitrary event type.
问题是我认为EventBus完成的反射操作不喜欢我的任何事件类型的泛型。
Essentially, the method accepts a BiConsumer where C is a Swing Component and E is an arbitrary event type to subscribe to EventBus. 本质上,该方法接受BiConsumer,其中C是Swing组件,E是订阅EventBus的任意事件类型。
public <E> void subscribe(EventBus eventBus, BiConsumer<C,E> consumer) {
eventBus.register(new Object() {
@Subscribe
public void processEvent(E event) {
try {
consumer.accept(comp, event);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
The event bus seems to be working but I keep getting bizarre ClassCastException
errors. 事件总线似乎正在工作但我不断收到奇怪的
ClassCastException
错误。 Is there any way I can make this work? 有什么方法可以让我的工作吗? Or is what I'm trying to achieve a lost cause?
或者我正在努力实现失败的原因?
UPDATE: Here is an SSCCE. 更新:这是一个SSCCE。 It breaks when there are multiple event types, and somewhere the generics and internal reflection mechanisms get messed up and it can't distinguish one event type from another.
当存在多个事件类型时,它会中断,并且泛型和内部反射机制会混乱,并且无法将一种事件类型与另一种事件类型区分开来。
import java.awt.Component;
import java.util.function.BiConsumer;
import javax.swing.JButton;
import com.google.common.eventbus.EventBus;
import com.google.common.eventbus.Subscribe;
public class EventBusTest<C extends Component> {
private final C comp;
public static void main(String[] args) {
final EventBus eventBus = new EventBus();
EventBusTest<JButton> test = new EventBusTest<>(new JButton("Hello"));
test.subscribe(eventBus, (JButton c, SomeEvent e) -> System.out.println("Hello"));
test.subscribe(eventBus, (JButton c, SomeOtherEvent e) -> System.out.println("World"));
eventBus.post(new SomeEvent());
}
private EventBusTest(C comp) {
this.comp = comp;
}
public<E> void subscribe(EventBus eventBus, BiConsumer<C,E> consumer) {
eventBus.register(new Object() {
@Subscribe
public void processEvent(E event) {
try {
consumer.accept(comp, event);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
private static final class SomeEvent {}
private static final class SomeOtherEvent {}
}
And here is the console print... 这是控制台打印......
java.lang.ClassCastException: com.swa.rm.pricing.EventBusTest$SomeEvent cannot be cast to com.swa.rm.pricing.EventBusTest$SomeOtherEvent
at com.swa.rm.pricing.EventBusTest$$Lambda$14/28594521.accept(Unknown Source)
at com.swa.rm.pricing.EventBusTest$1.processEvent(EventBusTest.java:32)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74)
at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
at com.google.common.eventbus.EventBus.post(EventBus.java:275)
at com.swa.rm.pricing.EventBusTest.main(EventBusTest.java:21)
Hello
The type parameter E
in your anonymous Object
subclass in subscribe()
will always be erased, since there is no concrete type to reify it. subscribe()
中的匿名Object
子类中的类型参数E
将始终被擦除,因为没有具体的类型来重新定义它。 The erasure of E
is just Object
, so nothing prevents your processEvent()
method from being called with any type. E
的擦除只是Object
,所以没有什么能阻止你的processEvent()
方法被任何类型调用。
To fix this, you'll need to pass a type token ( Class<E>
will probably suffice) and use it to check that the runtime type is actually E
before invoking the BiConsumer
callback. 要解决此问题,您需要传递一个类型标记(
Class<E>
可能就足够了),并在调用BiConsumer
回调之前使用它来检查运行时类型是否为E
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