RxFirebase | simple library that provides utilities | Reactive Programming library

I'm trying to fetch data from Firebase using RxSwift. I'm using this to perform API calls.

So my db looks like this: Collection Category (it has properties: title, about etc) has inside of it another collection called Manifests. To get Manifests I need to use documentId of Category collection. So it's two different API calls but I want to combine results

That is what I have so far:

I am new to RxJava and RxFirebase and I am making a register system for my app. All the steps in the registrations process need to happen in a sequence and this sequence needs to abort if a step fails.

This is code from my register UI class. I call register() on another class and subscribe on the return value, which is a Maybe.

I've this query to a firebase database that returns a boolen to indicate a child value exists. I'm using Rx2Firebase's wrappers to simplify queries:

I am reviewing an app build in Vuejs (I am not a vue developer), so be patient with me.

I found this line of code:

I'm currently having an issue during some of my users who log-in with email and password. The case is that after send the verification email, I'm calling reload in my current FirebaseUser to update the currentUser an know if the email have been verified or not.

Everything works fine at this point. The thing is that sometimes after call reload over an instance of FirebaseAuth.currentUser.reload(), on the successful callback of reload I'm trying to access again to the already updated FirebaseAuth.currentUser instance, and the funny thing is that this comes to be null and I'm getting a NPE, when the user have been successfully reloaded and the instance should be updated, not deleted.

This is my code right now:

I'm using this library for wrapping Firebase transactions with RxJava. I'm new to RxJava, so this is mainly a question regarding how to use it.

Scenario: There is a many-to-many relationship between Persons and Labels. A Person can have multiple Labels, and a Label can be given to many Persons. When a Person is created, I must:

• add them to the list of Persons
• update each Label given to them to allow for querying all Persons that belong to a specific label

I have a list of Labels I want to write to my Firebase database.

I'm developing application wherein I want to use MVVM pattern. Currently, all events from xml are handled by the activity which pass them next to ViewModel. E.g. user clicks login button, the event is handled by activity; now the activity call view model's method, inside this method I'm calling RxFirebase (Rx wrapper on Firebase) method which returns Observable, subscribe to them and return it; in view I'm again subscribe to this observable for doing UI update. This situation is presented below.

My question is if this approach is correct? In my opinion, the better solution is to handle the error in ViewModel, but how then I can update UI? One of the solutions is to create interface, e.g. ShowMessageListener, next pass it to ViewModel and use to show message, but I prefer harness RxJava to this.

View method:

I use RxFirebaseDatabase by https://github.com/ezhome/Android-RxFirebase. How do I delay subscription of observeValueEvent ? My code

Fragment.java