Generated indexes do not work on API <= 8

[nikclayton]

tl;dr: Eventbus should automatically ignore the generated index on devices <= API 8, and probably log a warning message.

findSubscriberMethods looks for methods using either findUsingReflection or findUsingInfo depending on whether the generated index is provided.

    List<SubscriberMethod> findSubscriberMethods(Class<?> subscriberClass) {
        List<SubscriberMethod> subscriberMethods = METHOD_CACHE.get(subscriberClass);
        if (subscriberMethods != null) {
            return subscriberMethods;
        }

        if (ignoreGeneratedIndex) {
            subscriberMethods = findUsingReflection(subscriberClass);
        } else {
            subscriberMethods = findUsingInfo(subscriberClass);
        }
        if (subscriberMethods.isEmpty()) {
            throw new EventBusException("Subscriber " + subscriberClass
                    + " and its super classes have no public methods with the @Subscribe annotation");
        } else {
            METHOD_CACHE.put(subscriberClass, subscriberMethods);
            return subscriberMethods;
        }
    }

If there's a generated index then findUsingInfo calls getSubscriberMethods which calls getSubscriberMethods which calls createSubscriberMethod which looks like:

    protected SubscriberMethod createSubscriberMethod(String methodName, Class<?> eventType, ThreadMode threadMode,
                                                      int priority, boolean sticky) {
        try {
            Method method = subscriberClass.getDeclaredMethod(methodName, eventType);
            return new SubscriberMethod(method, eventType, threadMode, priority, sticky);
        } catch (NoSuchMethodException e) {
            throw new EventBusException("Could not find subscriber method in " + subscriberClass +
                    ". Maybe a missing ProGuard rule?", e);
        }
    }

This throws NoSuchMethodException. However, it doesn't seem to be the NoSuchMethodException that getDeclaredMethod throws. It's thrown because, on devices running API 8 and below, the method getDeclaredMethod does not exist.

This results in a confusing exception message (it's got nothing to do with ProGuard).

Quick fix would be to modify addIndex to be something like

    /** Adds an index generated by EventBus' annotation preprocessor. */
    public EventBusBuilder addIndex(SubscriberInfoIndex index) {
        if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.FROYO) {
            Log.w(TAG, "Running on API < 9, ignoring generated index");
            return this;
        }
        if(subscriberInfoIndexes == null) {
            subscriberInfoIndexes = new ArrayList<>();
        }
        subscriberInfoIndexes.add(index);
        return this;
    }

and note this in the documentation.