RxJava wrapper for startActivityForResult and onActivityResult flow. Don't break the chain!

ObservableActivityForResult.java

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;

import com.mywebgrocer.util.ActivityResultData;

import java.util.Random;

import rx.Single;
import rx.subjects.PublishSubject;

/**
 * Wraps an activity that is launched for a result (`startActivityForResult`), exposing it as an observable.
 * THIS CLASS IS NOT THREAD-SAFE.
 *
 * @author David Whitman on Apr 28, 2017.
 */
public class ObservableActivityForResult extends AppCompatActivity {
    private static int REQUEST_CODE = -1;
    private static final String EXTRA_INTENT_TO_LAUNCH = "EXTRA_INTENT_TO_LAUNCH";
    private static PublishSubject<ActivityResultData> resultSubject;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        startActivityForResult(getIntent().getParcelableExtra(EXTRA_INTENT_TO_LAUNCH), REQUEST_CODE);
    }

    /**
     * Convenience method to create an instance of this class and launch the activity.
     * Emits a result based on the result of the activity, then finishes.
     * Should never call `onError`.
     * Do not call this method in parallel, it will make bad things happen.
     */
    public static Single<ActivityResultData> startActivityForResult(@NonNull Context context, @NonNull Intent intentToLaunch) {
        // Use Single.create so that resultSubject isn't assigned until the Single is subscribed to.
        // Otherwise, this would not work properly if the user wanted to chain two calls
        // because the resultSubject wouldn't get reinstantiated when the second Single was subscribed to.
        return Single.create(s -> {
            // Use random int for each call so a previous result can't somehow intrude on a subsequent one
            REQUEST_CODE = new Random().nextInt(32767); // Can only use lower 16 bits for request code
            resultSubject = PublishSubject.create();
            final Intent intent = new Intent(context, ObservableActivityForResult.class);
            intent.putExtra(EXTRA_INTENT_TO_LAUNCH, intentToLaunch);
            context.startActivity(intent);
            resultSubject.toSingle().subscribe(s);
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == REQUEST_CODE) {
            resultSubject.onNext(new ActivityResultData(requestCode, resultCode, data));
            resultSubject.onCompleted();
            finish();
        } else {
            super.onActivityResult(requestCode, resultCode, data);
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();

        if (!resultSubject.hasCompleted()) {
            resultSubject.onCompleted();
        }

        resultSubject = null;
    }
}