GreenRobot EventBus subscribe based on API level

Question

I'm attempting to subscribe to an EventBus event. Due to the parent class not existing in API level 23 and below, I'm in a situation where I need to conditionally subscribe to said event.

I realize that, through the use of build variants, it is possible to get around this, but I'm curious if there's a more elegant solution. The @RequiresApi annotation doesn't seem to have any effect (maybe stacking annotations doesn't work the way I expect it to).

Some simplified sample code:

class MyClass : OtherClass() {
    @Subscribe(threadMode = ThreadMode.MAIN)
    fun onSomeEvent(someEvent: SomeEvent) {
        // do some stuff
    }
}

Assuming OtherClass() is only available in API level 24+, the app will hang on the splash screen on lower API levels right after Dalvik or the ART realizes that the generated EventBusIndex references a broken class.

`@RequiresApi` has no effect on runtime behavior -- it is there for Lint to be smarter about what it warns you about. Do you get this crash even if you do not call `register()` to register your subscriber? — CommonsWare, Jul 22 '19 at 18:48
@CommonsWare Even after commenting out any `register()`/`unregister()` calls it will still hang on the splash screen due to the EventBusIndex. — michael, Jul 22 '19 at 18:51
OK, if you disable the EventBusIndex annotation processor, and do not register this subscriber on the older device, does it work? — CommonsWare, Jul 22 '19 at 19:06
@CommonsWare Disabling the EventBus annotation processor (and thereby also having to disable adding the index to the default event bus) will, as expected, fix the issue. — michael, Jul 22 '19 at 19:16
There's nothing stopping EventBus' annotation processor from either paying attention to something like `@RequiresApi` or having their own similar annotation property. My guess is that would require a feature request and some work on their part. — CommonsWare, Jul 22 '19 at 19:17
@CommonsWare Yeah, figures. Do you know of any way to get around this in the meantime without needing to create more build variants? — michael, Jul 22 '19 at 19:19
You could refactor your code such that your subscriber is not extending a class that may or may not exist (e.g., have `MyClass` hold something that is the subscriber, rather than being the subscriber itself). Or you could disable the annotation processor. Other than those two options and the build variant solution, I don't have any great ideas -- sorry! — CommonsWare, Jul 22 '19 at 19:21

score 1 · Accepted Answer · answered Jul 22 '19 at 19:26

You could try to tweak MyClass somewhat to move the subscription to another object:

class MyClass : OtherClass() {
    val subber = Subber()

    fun onSomeEventForRealz(someEvent: SomeEvent) {
        // do some stuff
    }

    inner class Subber {
        @Subscribe(threadMode = ThreadMode.MAIN)
        fun onSomeEvent(someEvent: SomeEvent) = onSomeEventForRealz(someEvent)
    }
}

You would also need to adjust your subscribe() and unsubscribe() calls to pass in subber instead of the MyClass instance itself.

GreenRobot EventBus subscribe based on API level

1 Answers1