Android RxJava2 App crashing on calling emitter.onError() from created observable

user_1852343 0
Viewed 3334

I am creating Observable manually with the help of create(). now inside, I check some conditions & based on that, I would like to notify the subscriber about error. Here's how I am creating observable:

public Observable<User> loginUser(String email, String password) {
    return Observable.create(
        emitter -> {
            myAsynchronousWork.onCompleteListener(
               result -> {
                   if(!result.isSuccess()) {
                      // This causes the crash.
                      emitter.onError(new Throwable(result.getError()));
                   } else {
                      // Process result & create User object & return it. This works as expected.
                      emitter.onNext(user);
                      emitter.onComplete();
                   }
               }
            );

        }
    );

}

& then I subscribe to loginUser() like:

loginUser("", "")
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(user -> {
                    Log.d("TAG", "logged in user => " + user.getUuid());
                    Log.d("TAG", "user name => " + user.getUserName());
                    Log.d("TAG", "user email => " + user.getEmailId());
                }, throwable -> {
                    Log.e("TAG", "error in login => " + throwable.getMessage());
                }, () -> {

                });

I expect that calling emitter.onError() should go inside onError of subscribe() of loginUser() where I have Logged the exception, but instead the app gets crashes with the Exception returned by emitter.onError() in logcat like there's no one to handle it!

I checked by debugging & found that while it's on line emitter.onError(), emitter was "null". however onNext & onComplete doesn't cause any problem. Please let me know where I am doing wrong?

rx-java2 android
3 Answers

The reason why my app was getting crashed was, I had actually something like this:

myAsynchronousWork.onCompleteListener(
               result -> {
                   if(!result.isSuccess()) {
                      // This causes the crash.
                      emitter.onError(new Throwable(result.getError()));
                   } else {
                      // Process result & create User object & return it. This works as expected.
                      emitter.onNext(user);
                      emitter.onComplete();
                   }
               },
               exception -> {
                   emitter.onError(exception); // This was the reason of problem!
               }
            );

I didn't posted the full part because I didn't get that it was causing the exception.

What happening here was, my code first was going inside the exception-> part which was notifying the observer about the error & that observer was getting terminated. now my result-> part was getting executed & here when I tried to call again emitter.onError(), it was crashing as there was no emitter to handle this & RxJava2 was throwing it globally.

So for me, I removed the exception -> part as it was any how going to be on result -> where I could check the result & I have also wrapped the emitter.onError with 

if(!emitter.isDisposed()) emitter.onError();

because in my case, it was fine to ignore the error if emitter was disposed.

user_18523430

Using emitter.tryOnError works for me and it will call error inside subscribe() as well without UndeliverableException or app stop running.

user_100530460

When you are creating observable you have to handle all possible errors yourself. so your code should look something like below:

public Observable<User> loginUser(String email, String password) {
    return Observable.create(
        emitter -> {
          try{
            myAsynchronousWork.onCompleteListener(
               result -> {
                 try{
                   if(!result.isSuccess()) {
                      // This causes the crash.
                      emitter.onError(new Throwable(result.getError()));
                   } else {
                      // Process result & create User object & return it. This works as expected.
                      emitter.onNext(user);
                      emitter.onComplete();
                   }
                 }catch(Exception e){
                    emitter.onError(e);
                 }
               }
            );
         }catch(Exception e){
            emitter.onError(e);
        }

        }
    );

}

PS: Always ensure error checking when creating observable and disposable too.

user_50802290
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