EventBus: all child classes receive event

Question

I have BaseActivity with fun onEvent(event: MyEvent) and 4 activities that extend the BaseActivity. My problem is that BaseActivity handles all the events. That means when an event is sent, it is received by all subclasses of BaseActivity that are instantiated at the moment, which causes onEvent() to run multiple times

class BaseActivity {
    ...
    fun onEvent(event: MyEvent) {
        //do some cool stuff
    }
}

class A: BaseActivity {

}

class B: BaseActivity {

}


class SomeClass {

    fun somefun() {
        EventBus.getDefault().post(MyEvent("woadude"));
    }
}

So in this case onEvent in BaseActivity is called 2 times for each subclass.

"When I send a MyEvent, all 4 classes receive it" -- classes do not. Objects do. Instances of your activities receive the events. "I need a way to only receive the event once" -- what do you mean by that? Do you mean that you only want the foreground activity to receive the event? Do you mean that you only want class A to receive the event? In other words, you need to decide what your criteria are for which objects will receive what events. — CommonsWare, Jan 12 '18 at 19:03
Please note that your edit did not answer the question of what you mean by "I need a way to only receive the event once for a certain activity". Specifically, what **precisely** is the criteria for which activity instance is "a certain activity"? — CommonsWare, Jan 12 '18 at 19:18

Leandro Ocampo · Accepted Answer · 2018-01-12T21:03:10.097

If you want different messages for different objects then you need to create different structures. In your case, you want to send a message to object A and another message to object B base on some logic (which I do not know).

My solution is to create a MyEvent inside class A, and MyEvent in class B (I know, probably is not so good as parent classes shouldn't know about children). Then your logic will be like this:

fun somefun() {
  if("some condition"){
    EventBus.getDefault().post(A.MyEvent("woadude"));
  }if("another condition") {
    EventBus.getDefault().post(B.MyEvent("woadude"));
  }      
 }

Another option is just to create different classes MyEventA and MyEventB, and each object from different classes can register to MyEventA and MyEventB respectively. With this way, you parent class does not need to know anything about children.

Whatever solution you choose, the solution is that you need to sent different object types in order to make it work

EDIT base on the new information you need to remove this function from BaseActivity

   fun onEvent(event: MyEvent) {
        //do some cool stuff
    }

and make it abstract. Use MyEvent as the parent class of each MyEvent class for you are going to create. So you will have:

MyEventA : MyEvent

MyEventB: MyEvent

then in class A you will have

fun onEvent(event: MyEventA) {
        //do some cool stuff
    }

and in class B

fun onEvent(event: MyEventB) {
        //do some cool stuff
    }

Of course, my answer could be better if you give more information about the problem.

Hope it helps.

Not sure if this is the solution. My problem is that BaseActivity handles all the events. That means when an event is sent, it is received by all subclasses of BaseActivity that are instantiated at the moment, which causes onEvent() to run multiple times. I guess I need to target it at desired class somehow. — Sermilion, Jan 12 '18 at 20:54
@Sermilion my answer was updated according to the new information you gave me! good luck :) — Leandro Ocampo, Jan 12 '18 at 21:03
Is it possible to register for two different subscribers from two different places in the same activity? — Rahulrr2602, May 29 '19 at 15:58

EventBus: all child classes receive event

1 Answers1