Android-Architecture | : city_sunrise : 该项目结合 MVP 与 Clean 架构思想，探索在 | Architecture library

I'm following along this blog for using Android Architecture Components with Firebase Realtime Database. Currently, I am at the part of the blog where I move the LiveData callbacks to onChanged() onto a different thread.

This is what I have (the Kotlin equivalent of the Java code from the blog):

I am following an old tutorial about LiveData and ViewModel.These are the links.

1. [https://www.youtube.com/watch?v=d7UxPYxgBoA][1]
2. [https://resocoder.com/2018/09/07/mvvm-on-android-crash-course-kotlin-android-architecture-components/]

I am getting an error in InjectUtil.kt class while initiating FakeDatabase class and getting it's variable. I am following the tutorial and do not know why I am getting it.

I added some new code to my recyclerView which deletes the item when swiped either to the left or right, but when I move to a different activity, and then come back to my recyclerView activity, the items reappear. Here is the code of my MainActivity(called TestGroceryList):

I used this link for pass parameter to ViewModel constructor when pass one parameter no problem

I read these blog posts written by Doug Stevenson Part 1, Part 2, Part 3. On part 2 he says that

The Realtime Database SDK makes it really easy to convert a DataSnapshot into a JavaBean style object

And mentions that we can use this line of code to get the DataSnapshot deserialized into a HotStock object (a JavaBean class)

HotStock stock = dataSnapshot.getValue(HotStock.class)

I´m confused because he first uses Transformation.map and then he says that if a LiveData transformation is expensive we can create a MediatorLiveData object from the ViewModel to get the DataSnapshot converted into a HotStock object.

My question is: Why can´t we just call the

HotStock stock = dataSnapshot.getValue(HotStock.class)

from the onDataChange() method on the ValueEventListener which resides in the class extending the LiveData super class and then simply use the setValue() method to pass the HotStock object directly to the ViewModel and then to the Activity or Fragment observing for changes to the LiveData?