Guava EventBus延迟嵌套事件的处理程序执行

Question

public void parentEventHandler(ParentEvent parentEvent) {
    Object nestedEvent = createNestedEvent();
    eventBus.post(nestedEvent);

    if(nestedEvent.isCancelled()) {
        return;
    }

    Object anotherNestedEvent = createOtherNestedEvent();
    eventBus.post(anotherNestedEvent);
}

1. parentEvent is posted
2. parentEventHandler is called
3. nestedEvent is posted
4. handlers of nestedEvent are called
5. finished handling nestedEvent
6. if statement checks for cancel state of nestedEvent
7.     anotherNestedEvent is posted if nestedEvent not cancelled
8.     handlers of anotherNestedEvent are called
9.     finished handling anotherNestedEvent
10 finished handling parentEvent

正在发生的事情：

1. parentEvent is posted
2. parentEventHandler is called
3. nestedEvent is posted
4. if statement checks for cancel state of nestedEvent (defaults to false)
5.     anotherNestedEvent is posted
6. finished handing parentEvent
7. handlers of nestedEvent are called
8. nestedEvent is cancelled (too late now)
9. finished handling nestedEvent
10 handlers of anotherNestedEvent are called
11 finished handling anotherNestedEvent

在第8点。无论处理程序是否取消事件，由于取消检查默认为false，第二个事件已经排队。Guava的EventBus坚持在启动下一个事件之前完成当前的处理程序运行，我确信这有其用处，但这不是我想要的。

尝试黑客：

Answer 1

如果您使用的是“常规”EventBus，那么您可以通过创建一个辅助事件来使其工作。

添加接口InternalEventCallback和类InternalEventCallbackHandler:

interface InternalEventCallback {
    void run();
}

class InternalEventCallbackHandler {

    @Subscribe
    public void internalEventHandler(InternalEventCallback r){
        r.run();
    }
}

在创建EventBus的地方，注册InternalEventCallbackHandler:

eventBus.register(new InternalEventCallbackHandler());

@Subscribe
public void parentEventHandler(ParentEvent parentEvent) {
    NestedEvent nestedEvent = createNestedEvent();
    eventBus.post(nestedEvent);
    eventBus.post(new InternalEventCallback() {
        @Override
        public void run() {
            if(nestedEvent.isCancelled()) {
                return;
            }

            Object anotherNestedEvent = createOtherNestedEvent();
            eventBus.post(anotherNestedEvent);
        }
    });
}

EventBus eventBus = new AsyncEventBus(MoreExecutors.newDirectExecutorService());