Android Architecture Components

Question 1

When to use RxJava in Android and when to use LiveData from Android Architectural Components?

Answer 1

There are many differences between LiveData and RxJava:

1. LiveData is not a STREAM while in RxJava everything (literally everything) is a STREAM.
2. LiveData is an observable data holder class. Unlike a regular observable, LiveData is lifecycle-aware, meaning it respects the lifecycle of other app components, such as activities, fragments, or services. This awareness ensures LiveData only updates app component observers that are in an active lifecycle state.
3. LiveData is synchronous, So you can’t execute a chunk of code (network call, database manipulation etc.) asynchronously using just LiveData as you do with RxJava.
4. What best you can do to exploit the most of this duo is to use RxJava for your business logic (network call, data manipulation etc, anything that happens in and beyond Repository) and use LiveData for your presentation layer. By this, you get transformation and stream capabilities for your business logic and lifecycle-aware operation for your UI.
5. LiveData and RxJava compliment each other if used together. What I mean is, do everything with RxJava and at the end when you want to update UI, do something like the code given below to change your Observable into LiveData. So, your View (UI) observes to the LiveData in ViewModel where your LiveData is nothing but non-mutable MutableLiveData (or MutableLiveData is mutable LiveData).
6. So the question here is, why should you even use LiveData at the first place? As you can see below in the code, you store your response from RxJava to MutableLiveData (or LiveData) and your LiveData is lifecycle-aware, so in a way, your data is lifecycle-aware. Now, just imagine the possibility when your data itself know when and when-not-to update the UI.
7. LiveData doesn’t have a history (just the current state). Hence, you shouldn’t use LiveData for a chat application.
8. When you use LiveData with RxJava you don’t need stuff like MediatorLiveData, SwitchMap etc. They are stream control tools and RxJava is better at that by many times.
9. See LiveData as a data holder thing and nothing else. We can also say LiveData is lifecycle-aware consumer.
10. Android LiveData is a variant of the original observer pattern, with the addition of active/inactive transitions. As such, it is very restrictive in its scope.

The point of RxJava is that it combines control and timing into a single universe, using operations provided from the library, or even custom operations that you provide.
LiveData addresses only one small part of that universe, the equivalent of building the liveLocation.